@article{simon_binderup_flecker_gilliam_marshall_thomas_travis_reznick_pringle_2019, title={Landscape patterns in top-down control of decomposition: omnivory disrupts a tropical detrital-based trophic cascade}, volume={100}, ISBN={1939-9170}, DOI={10.1002/ecy.2723}, abstractNote={AbstractDetrital‐based trophic cascades are often considered weak or absent in tropical stream ecosystems because of the prevalence of omnivorous macroconsumers and the dearth of leaf‐shredding insects. In this study, we isolate top‐down effects of three macroconsumer species on detrital processing in headwater streams draining Trinidad's northern mountains. We separated effects of different macroconsumers by experimentally manipulating their temporal access to isolated benthic habitat over the diel cycle. We found no evidence that omnivorous macroconsumers, including a freshwater crab (Eudaniela garmani) and guppy (Poecilia reticulata), increased leaf decomposition via consumption. By contrast, above a waterfall excluding guppies, the insectivorous killifish, Anablepsoides hartii, reduced the biomass of the leaf‐shredding insect Phylloicus hansoni 4‐fold, which consequently reduced leaf decomposition rates 1.6‐fold. This detrital cascade did not occur below the barrier waterfall, where omnivorous guppies join the assemblage and reduce killifish densities; here killifish had no significant effects on Phylloicus or decomposition rates. These patterns of detrital processing were also observed in upstream–downstream comparisons in a landscape study across paired reaches of six streams. Above waterfalls, where killifish were present, but guppies absent, leaf decomposition rates and Phylloicus biomass were 2.5‐ and ~35‐fold lower, respectively, compared to measurements below waterfalls. Moreover, the strength of top‐down control by killifish is reflected by the 20‐ and 5‐fold reductions in variability (±SE) surrounding mean Phylloicus biomass and leaf decomposition rates in upstream relative to downstream reaches where no top‐down control was detected. Findings show a clear, detrital‐based trophic cascade among killifish, a leaf‐shredding insect, and leaf decomposition rates. Results also show how omnivorous guppies disrupt this cascade by depressing killifish densities, thereby releasing invertebrate shredders from predation, and significantly increasing decomposition rates. Moreover, this combination of direct and indirect trophic interactions drives patterns in decomposition rates in stream networks at a landscape scale, resulting in significantly lower rates of decomposition above vs. below barrier waterfalls. Our findings reveal that omnivory can result in significant indirect effects on a key ecosystem process, illustrating the importance of these hidden trophic pathways in detrital‐based systems and suggesting that resource control in tropical systems may be even more complex than previously envisioned.}, number={7}, journal={ECOLOGY}, author={Simon, Troy N. and Binderup, Andrew J. and Flecker, Alex S. and Gilliam, James F. and Marshall, Michael C. and Thomas, Steven A. and Travis, Joseph and Reznick, David N. and Pringle, Catherine M.}, year={2019}, month={Jul} }
 @article{hain_moody_lamphere_nelson_mcintyre_gilliam_blum_2019, title={Migratory gauntlets on oceanic islands: Watershed disturbance increases the cost of amphidromy}, volume={28}, ISSN={0906-6691 1600-0633}, url={http://dx.doi.org/10.1111/eff.12467}, DOI={10.1111/eff.12467}, abstractNote={AbstractMigratory fishes can be threatened by conditions encountered along dispersal pathways that impede access to feeding or breeding grounds. In this study, we tested the hypothesis that amphidromous fishes are equally or more sensitive to conditions along dispersal pathways than conditions in primary residential habitats. We did so by conducting distribution‐wide population surveys of all five amphidromous gobies native to the Hawaiian Islands to assess responses to in‐stream habitat, invasive species and watershed land use. We used Redundancy Analyses to assess whether goby densities varied according to local, downstream or upstream conditions. We found that population densities of the two non‐climbing species (Eleotris sandwicensis, Stenogobius hawaiiensis) varied according to local land use and local habitat conditions. Greater densities of E. sandwicensis also were found in watersheds with greater forest cover upstream of survey sites. Lower densities of two species that migrate farther inland (Awaous stamineus, Sicyopterus stimpsoni) were observed in watersheds with greater anthropogenic land use downstream or at the stream mouth. Population densities of E. sandwicensis and both Sicydiine species (Lentipes concolor, S. stimpsoni) also were lower when non‐native Poeciliids were locally present or present downstream in the watershed. These findings suggest that densities of native Hawaiian amphidromous fishes are equally or more sensitive to conditions along migratory pathways relative to conditions in primary residential habitats. Thus, alleviating pressures by removing invasive species and restoring habitat along dispersal pathways could be effective approaches to increasing densities of amphidromous species, especially those that migrate farther inland to higher elevations.}, number={3}, journal={Ecology of Freshwater Fish}, publisher={Wiley}, author={Hain, Ernie F. and Moody, Kristine N. and Lamphere, Bradley A. and Nelson, Stacy A. C. and McIntyre, Peter B. and Gilliam, James F. and Blum, Michael J.}, year={2019}, month={Feb}, pages={446–458} }
 @article{lisi_childress_gagne_hain_lamphere_walter_hogan_gilliam_blum_mcintyre_2018, title={Overcoming urban stream syndrome: Trophic flexibility confers resilience in a Hawaiian stream fish}, volume={63}, ISSN={["1365-2427"]}, DOI={10.1111/fwb.13091}, abstractNote={Abstract


Urbanisation is widely associated with a suite of physical, chemical and biological degradation of stream ecosystems, known as “urban stream syndrome.” It is unclear whether urban stream syndrome is applicable to oceanic islands, where marine dispersal of larvae enables diadromous species to continuously recolonise even highly degraded urban streams.

The depauperate native fauna of oceanic island streams can be entirely composed of diadromous species, but urban streams food webs are often dominated by introduced predators, competitors and functional groups derived from continental systems. Despite these challenges, some native species appear to thrive in urbanised catchments.

Here, we test for urban stream syndrome on oceanic islands by quantifying catchment land use, nutrient concentrations and fish community composition for 37 streams across the Hawaiian archipelago. To assess how native species adapt to food webs altered by species introductions, we quantified trophic responses by examining stomach contents, nitrogen stable isotopes and body condition of Awaous stamineus (an omnivorous goby) in each stream.

Urbanisation was consistently associated with nitrogen pollution and replacement of native species with more tolerant exotics. Population densities of three of five native goby species declined sharply with urbanisation, whereas the two other native gobies species were resilient.

The trophic position of the omnivore A. stamineus was elevated in urban streams compared to forested catchments, reflecting a shift in stomach contents from algae to greater reliance on exotic aquatic and terrestrial invertebrates. Comparable body condition and resilient population density of A. stamineus across the urbanisation gradient suggest that dietary flexibility buffers this species against environmental degradation.

Our findings indicate that the concept of urban stream syndrome is applicable to oceanic islands, yet A. stamineus shows striking resilience. Flexibility in diet, life history and habitat use of this native goby appear to buffer it against the effects of urbanisation compared to most other amphidromous fishes in Hawaiian streams.

}, number={5}, journal={FRESHWATER BIOLOGY}, author={Lisi, Peter J. and Childress, Evan S. and Gagne, Roderick B. and Hain, Ernie F. and Lamphere, Brad A. and Walter, Ryan P. and Hogan, J. Derek and Gilliam, James F. and Blum, Michael J. and McIntyre, Peter B.}, year={2018}, month={May}, pages={492–502} }
 @article{gagne_sprehn_alda_mcintyre_gilliam_blum_2018, title={Invasion of the Hawaiian Islands by a parasite infecting imperiled stream fishes}, volume={41}, ISSN={["1600-0587"]}, DOI={10.1111/ecog.02855}, abstractNote={Points of origin and pathways of spread are often poorly understood for introduced parasites that drive disease emergence in imperiled native species. Co‐introduction of parasites with non‐native hosts is of particular concern in remote areas like the Hawaiian Islands, where the introduced nematode Camallanus cotti has become the most prevalent parasite of at‐risk native stream fishes. In this study, we evaluated the prevailing hypothesis that C. cotti entered the Hawaiian Islands with poeciliid fishes from the Americas, and spread by translocation of poeciliid hosts across the archipelago for mosquito control. We also considered the alternative hypothesis of multiple independent co‐introductions with host fishes originating from Asia. We inferred conduits of introduction and spread of C. cotti across the archipelago from geographic patterns of mtDNA sequence variation and allelic variation across 11 newly developed microsatellite markers. The distribution of haplotypes suggests that C. cotti spread across the archipelago following an initial introduction on O'ahu. Approximate Bayesian Computation modeling and allelic variation also indicate that O'ahu is the most likely location of introduction, from which C. cotti dispersed to Maui followed by spread to the other islands in the archipelago. Evidence of significant genetic structure across islands indicates that contemporary dispersal is limited. Our findings parallel historical records of non‐native poeciliid introductions and suggest that remediating invasion hotspots could reduce the risk of infection in native stream fishes, which illustrates how inferences on parasite co‐introductions can improve conservation efforts by guiding responses to emerging infectious disease in species of concern.}, number={3}, journal={ECOGRAPHY}, author={Gagne, Roderick B. and Sprehn, C. Grace and Alda, Fernando and McIntyre, Peter B. and Gilliam, James F. and Blum, Michael J.}, year={2018}, month={Mar}, pages={528–539} }
 @article{simon_bassar_binderup_flecker_freeman_gilliam_marshall_thomas_travis_reznick_et al._2017, title={Local Adaptation in Trinidadian Guppies Alters Stream Ecosystem Structure at Landscape Scales despite High Environmental Variability}, volume={105}, ISSN={["1938-5110"]}, DOI={10.1643/ce-16-517}, abstractNote={While previous studies have shown that evolutionary divergence alters ecological processes in small-scale experiments, a major challenge is to assess whether such evolutionary effects are important in natural ecosystems at larger spatial scales. At the landscape scale, across eight streams in the Caroni drainage, we found that the presence of locally adapted populations of guppies (Poecilia reticulata) is associated with reduced algal biomass and increased invertebrate biomass, while the opposite trends were true in streams with experimentally introduced populations of non-locally adapted guppies. Exclusion experiments conducted in two separate reaches of a single stream showed that guppies with locally adapted phenotypes significantly reduced algae with no effect on invertebrates, while non-adapted guppies had no effect on algae but significantly reduced invertebrates. These divergent effects of phenotype on stream ecosystems are comparable in strength to the effects of abiotic factors (e.g., light) known to be important drivers of ecosystem condition. They also corroborate the results of previous experiments conducted in artificial streams. Our results demonstrate that local adaptation can produce phenotypes with significantly different effects in natural ecosystems at a landscape scale, within a tropical watershed, despite high variability in abiotic factors: five of the seven physical and chemical parameters measured across the eight study streams varied by more than one order of magnitude. Our findings suggest that ecosystem structure is, in part, an evolutionary product and not simply an ecological pattern.}, number={3}, journal={COPEIA}, author={Simon, Troy N. and Bassar, Ronald D. and Binderup, Andrew J. and Flecker, Alex S. and Freeman, Mary C. and Gilliam, James F. and Marshall, Michael C. and Thomas, Steven A. and Travis, Joseph and Reznick, David N. and et al.}, year={2017}, month={Sep}, pages={504–513} }
 @article{alda_gagne_walter_hogan_moody_zink_mcintyre_gilliam_blum_2016, title={Colonization and demographic expansion of freshwater fauna across the Hawaiian archipelago}, volume={29}, ISSN={["1420-9101"]}, DOI={10.1111/jeb.12929}, abstractNote={AbstractIt is widely accepted that insular terrestrial biodiversity progresses with island age because colonization and diversification proceed over time. Here, we assessed whether this principle extends to oceanic island streams. We examined rangewide mtDNA sequence variation in four stream‐dwelling species across the Hawaiian archipelago to characterize the relationship between colonization and demographic expansion, and to determine whether either factor reflects island age. We found that colonization and demographic expansion are not related and that neither corresponds to island age. The snail Neritina granosa exhibited the oldest colonization time (~2.713 mya) and time since demographic expansion (~282 kya), likely reflecting a preference for lotic habitats most prevalent on young islands. Conversely, gobioid fishes (Awaous stamineus, Eleotris sandwicensis and Sicyopterus stimpsoni) colonized the archipelago only ~0.411–0.935 mya, suggesting ecological opportunities for colonization in this group were temporally constrained. These findings indicate that stream communities form across colonization windows, underscoring the importance of ecological opportunities in shaping island freshwater diversity.}, number={10}, journal={JOURNAL OF EVOLUTIONARY BIOLOGY}, author={Alda, F. and Gagne, R. B. and Walter, R. P. and Hogan, J. D. and Moody, K. N. and Zink, F. and McIntyre, P. B. and Gilliam, J. F. and Blum, M. J.}, year={2016}, month={Oct}, pages={2054–2069} }
 @article{hain_lamphere_blum_mcintyre_nelson_gilliam_2016, title={Comparison of Visual Survey and Mark-Recapture Population Estimates of a Benthic Fish in Hawaii}, volume={145}, ISSN={["1548-8659"]}, DOI={10.1080/00028487.2016.1159610}, abstractNote={AbstractVisual surveys are conducted to rapidly estimate population densities of stream fishes, often without calibration against more established or more widely used methods to determine precision and accuracy or to correct for potential biases. We compared population density estimates from a visual survey (VS) point quadrat method widely used in Hawaii with estimates from “in hand” individual and batch mark–recapture (BMR) methods. Visual survey sampling and individual mark–recapture (IMR) sampling were conducted in three watersheds that represent gradients of land use and prevalence of nonnative poeciliid fishes on the Island of Hawaii. Focusing on adult O‘opu Nākea Awaous stamineus, VSs were conducted prior to IMR events to allow direct comparisons of results independent of location and time. Density estimates of O‘opu Nākea from VS and IMR samplings were strongly correlated, although VS estimates were generally higher and underrepresented exceptionally large fish. Batch mark–recapture estimates of O‘opu Nākea densities were conducted for comparison with VSs at 13 sites across the archipelago. Estimates of VSs were not significantly different from BMR estimates. Estimates of VSs also exhibited less variance than did BMR estimates across sites. General linear models showed that the relationship between VS and IMR estimates varied significantly among watersheds but not seasons and that land use was associated with a greater mismatch between VS and BMR estimates of population density. These findings indicate that visual surveys using a point quadrat method are an efficient and accurate approach for estimating the abundance of small benthic fishes, such as O‘opu Nākea, in wadeable streams and that obtaining absolute densities or size distributions from VS methods would benefit from a calibration with IMR not BMR estimates.Received July 15, 2015; accepted February 23, 2016 Published online June 29, 2016}, number={4}, journal={TRANSACTIONS OF THE AMERICAN FISHERIES SOCIETY}, author={Hain, Ernie F. and Lamphere, Bradley A. and Blum, Michael J. and McIntyre, Peter B. and Nelson, Stacy A. C. and Gilliam, James F.}, year={2016}, pages={878–887} }
 @article{gagne_heins_mcintyre_gilliam_blum_2016, title={Mutual dilution of infection by an introduced parasite in native and invasive stream fishes across Hawaii}, volume={143}, ISSN={["1469-8161"]}, DOI={10.1017/s0031182016001001}, abstractNote={SUMMARYThe presence of introduced hosts can increase or decrease infections of co-introduced parasites in native species of conservation concern. In this study, we compared parasite abundance, intensity, and prevalence between nativeAwaous stamineusand introduced poeciliid fishes by a co-introduced nematode parasite (Camallanus cotti) in 42 watersheds across the Hawaiian Islands. We found that parasite abundance, intensity and prevalence were greater in native than introduced hosts. Parasite abundance, intensity and prevalence withinA. stamineusvaried between years, which largely reflected a transient spike in infection in three remote watersheds on Molokai. At each site we measured host factors (length, density of native host, density of introduced host) and environmental factors (per cent agricultural and urban land use, water chemistry, watershed area and precipitation) hypothesized to influenceC. cottiabundance, intensity and prevalence. Factors associated with parasitism differed between native and introduced hosts. Notably, parasitism of native hosts was higher in streams with lower water quality, whereas parasitism of introduced hosts was lower in streams with lower water quality. We also found that parasite burdens were lower in both native and introduced hosts when coincident. Evidence of a mutual dilution effect indicates that introduced hosts can ameliorate parasitism of native fishes by co-introduced parasites, which raises questions about the value of remediation actions, such as the removal of introduced hosts, in stemming the rise of infectious disease in species of conservation concern.}, number={12}, journal={PARASITOLOGY}, author={Gagne, Roderick B. and Heins, David C. and Mcintyre, Peter B. and Gilliam, James F. and Blum, Michael J.}, year={2016}, month={Oct}, pages={1605–1614} }
 @article{hogan_kozdon_blum_gilliam_valley_mcintyre_2017, title={Reconstructing larval growth and habitat use in an amphidromous goby using otolith increments and microchemistry}, volume={90}, ISSN={["1095-8649"]}, DOI={10.1111/jfb.13240}, abstractNote={High‐resolution analysis of growth increments, trace element chemistry and oxygen isotope ratios (δ18O) in otoliths were combined to assess larval and post‐larval habitat use and growth of Awaous stamineus, an amphidromous goby native to Hawai‘i. Otolith increment widths indicate that all individuals experience a brief period of rapid growth during early life as larvae and that the duration of this growth anomaly is negatively correlated with larval duration. A protracted high‐growth period early in larval life is associated with a lower ratio of Sr:Ca, which may reflect low salinity conditions in nearshore habitats. A distinct shift in δ18O (range: 4–5‰) is closely associated with the metamorphic mark in otoliths, indicating that larval metamorphosis occurs promptly upon return to fresh water. Strontium and other trace elements are not as tightly coupled to the metamorphosis mark, but confirm the marine‐to‐freshwater transition. Integration of microstructural and microchemical approaches reveals that larvae vary substantially in growth rate, possibly in association with habitat differences. Although time and financial costs make it difficult to achieve large sample sizes, present results show that examining even a small number of individuals can lead to novel inferences about early life history in diadromous fishes and illustrates the value of integrating analyses.}, number={4}, journal={JOURNAL OF FISH BIOLOGY}, author={Hogan, J. D. and Kozdon, R. and Blum, M. J. and Gilliam, J. F. and Valley, J. W. and McIntyre, P. B.}, year={2017}, month={Apr}, pages={1338–1355} }
 @article{hogan_blum_gilliam_bickford_mcintyre_2014, title={Consequences of alternative dispersal strategies in a putatively amphidromous fish}, volume={95}, ISSN={["1939-9170"]}, DOI={10.1890/13-0576.1}, abstractNote={Successful dispersal can enhance both individual fitness and population persistence, but the process of dispersal is often inherently risky. The interplay between the costs and benefits of dispersal are poorly documented for species with complex life histories due to the difficulty of tracking dispersing individuals. Here we investigate variability in dispersal histories of a freshwater fish, Awaous stamineus, across the species' entire geographic range in the Hawaiian archipelago. Like many animals endemic to tropical island streams, these gobies have an amphidromous life cycle in which a brief marine larval phase enables dispersal among isolated freshwater habitats. Using otolith microchemistry, we document three distinct marine dispersal pathways, all of which are observed on every island. Surprisingly, we also find that 62% of individuals complete their life cycle entirely within freshwater, in contrast to the assumption that amphidromy is obligate in Hawaiian stream gobies. Comparing early life history outcomes based on daily otolith growth rings, we find that individuals with marine dispersal have shorter larval durations and faster larval growth, and their growth advantage over purely freshwater counterparts continues to some degree into adult life. These individual benefits of maintaining a marine dispersal phase presumably balance against the challenge of finding and reentering an island stream from the ocean. The facultative nature of amphidromy in this species highlights the selective balance between costs and benefits of dispersal in life history evolution. Accounting for alternative dispersal strategies will be essential for conservation of the amphidromous species that often dominate tropical island streams, many of which are at risk of extinction.}, number={9}, journal={ECOLOGY}, author={Hogan, J. Derek and Blum, Michael J. and Gilliam, James F. and Bickford, Nate and McIntyre, Peter B.}, year={2014}, month={Sep}, pages={2397–2408} }
 @article{gagne_hogan_pracheil_mcintyre_hain_gilliam_blum_2015, title={Spread of an introduced parasite across the Hawaiian archipelago independent of its introduced host}, volume={60}, ISSN={["1365-2427"]}, DOI={10.1111/fwb.12491}, abstractNote={Summary


Co‐introductions of non‐native parasites with non‐native hosts can be a major driver of disease emergence in native species, but the conditions that promote the establishment and spread of non‐native parasites remain poorly understood. Here, we characterise the infection of a native host species by a non‐native parasite relative to the distribution and density of the original non‐native host species and a suite of organismal and environmental factors that have been associated with parasitism, but not commonly considered within a single system.

We examined the native Hawaiian goby Awaous stamineus across 23 catchments on five islands for infection by the non‐native nematode parasite Camallanus cotti. We used model selection to test whether parasite infection was associated with the genetic diversity, size and population density of native hosts, the distribution and density of non‐native hosts, land use and water quality.

We found that the distribution of non‐native C. cotti parasites has become decoupled from the non‐native hosts that were primary vectors of introduction to the Hawaiian Islands. Although no single intrinsic or extrinsic factor was identified that best explains parasitism of A. stamineus by C. cotti, native host size, population density and water quality were consistently identified as influencing parasite intensity and prevalence.

The introduction of non‐native species can indirectly influence native species through infection of co‐introduced parasites. Here, we show that the effects of ‘enemy addition’ can extend beyond the range of non‐native hosts through the independent spread of non‐native parasites. This suggests that control of non‐native hosts is not sufficient to halt the spread of introduced parasites. Designing importation regulations to prevent host–parasite co‐introductions can promote native species conservation, even in remote areas that may not seem susceptible to human influence.

}, number={2}, journal={FRESHWATER BIOLOGY}, author={Gagne, Roderick B. and Hogan, J. Derek and Pracheil, Brenda M. and Mcintyre, Peter B. and Hain, Ernie F. and Gilliam, James F. and Blum, Michael J.}, year={2015}, month={Feb}, pages={311–322} }
 @article{beckmann_gilliam_brian langerhans_2015, title={X-ray imaging as a time-saving, non-invasive technique for diet analysis}, volume={161}, ISSN={0165-7836}, url={http://dx.doi.org/10.1016/J.FISHRES.2014.05.015}, DOI={10.1016/J.FISHRES.2014.05.015}, abstractNote={Dietary patterns of animals have a long-recognized importance in ecology and evolution, with numerous and diverse applications. While many methods of diet assessment exist, the most common method of direct diet examination for most small vertebrates is stomach-content analysis, using labor-intensive surgical removal of the gut following death. Methods that can reduce the time required to collect diet information without necessarily sacrificing specimens could prove invaluable for a range of applications. We evaluated digital X-ray imaging as a non-invasive method for examination of stomach contents of small fishes. Based on both a feeding experiment and examination of field-collected preserved specimens, we found that digital radiography consistently revealed the presence of moderate- to high-density prey items in the stomach, such as small arthropods. Moreover, X-ray imaging allowed for rapid identification of some particular prey items such as detritus, dipteran larvae, ostracods, hard-shelled molluscs, and small fish. However, this method failed to detect some low-density prey items present in some stomachs, and could not be used for precise taxonomic identifications in most cases. Overall, we found that digital X-ray images can be quickly acquired from anesthetized or preserved animals, permit rapid identification of certain prey items, and facilitate digital data archives. Future studies that employ this method should first “ground-truth” the radiological signatures of prey items observed within a given study using stomach-content analysis, which then permits rapid data collection strictly using X-ray images. This method can provide information useful for determining the inclusion of certain prey items in diets, even quantifying particular taxonomic groups of prey (% occurrence, % by number). Thus our results indicate that for certain study goals, X-ray radiography may provide a time reducing, non-invasive technique for diet analysis of small vertebrates.}, journal={Fisheries Research}, publisher={Elsevier BV}, author={Beckmann, Melanie C. and Gilliam, James F. and Brian Langerhans, R.}, year={2015}, month={Jan}, pages={1–7} }
 @article{phillip_taphorn_holm_gilliam_lamphere_lopez-fernandez_2013, title={ZOOTAXA Annotated list and key to the stream fishes of Trinidad & Tobago}, volume={3711}, DOI={10.11646/zootaxa.3711.1.1}, abstractNote={Based on historical and museum records and recent extensive collecting we compiled a checklist of 77 fish species reported from the streams of Trinidad and Tobago. A key with photographs is provided to aid in identifications, as well as brief notes on habitat, diet, reproduction, maximum size, local common names and distribution.}, number={1}, journal={Zootaxa}, author={Phillip, D. A. T. and Taphorn, D. C. and Holm, E. and Gilliam, J. F. and Lamphere, B. A. and Lopez-Fernandez, H.}, year={2013}, pages={1–64} }
 @article{el-sabaawi_kohler_zandona_travis_marshall_thomas_reznick_walsh_gilliam_pringle_et al._2012, title={Environmental and Organismal Predictors of Intraspecific Variation in the Stoichiometry of a Neotropical Freshwater Fish}, volume={7}, ISSN={["1932-6203"]}, DOI={10.1371/journal.pone.0032713}, abstractNote={The elemental composition of animals, or their organismal stoichiometry, is thought to constrain their contribution to nutrient recycling, their interactions with other animals, and their demographic rates. Factors that affect organismal stoichiometry are generally poorly understood, but likely reflect elemental investments in morphological features and life history traits, acting in concert with the environmental availability of elements. We assessed the relative contribution of organismal traits and environmental variability to the stoichiometry of an insectivorous Neotropical stream fish, Rivulus hartii. We characterized the influence of body size, life history phenotype, stage of maturity, and environmental variability on organismal stoichiometry in 6 streams that differ in a broad suite of environmental variables. The elemental composition of R. hartii was variable, and overlapped with the wide range of elemental composition documented across freshwater fish taxa. Average %P composition was ∼3.2%(±0.6), average %N∼10.7%(±0.9), and average %C∼41.7%(±3.1). Streams were the strongest predictor of organismal stoichiometry, and explained up to 18% of the overall variance. This effect appeared to be largely explained by variability in quality of basal resources such as epilithon N∶P and benthic organic matter C∶N, along with variability in invertebrate standing stocks, an important food source for R. hartii. Organismal traits were weak predictors of organismal stoichiometry in this species, explaining when combined up to 7% of the overall variance in stoichiometry. Body size was significantly and positively correlated with %P, and negatively with N∶P, and C∶P, and life history phenotype was significantly correlated with %C, %P, C∶P and C∶N. Our study suggests that spatial variability in elemental availability is more strongly correlated with organismal stoichiometry than organismal traits, and suggests that the stoichiometry of carnivores may not be completely buffered from environmental variability. We discuss the relevance of these findings to ecological stoichiometry theory.}, number={3}, journal={PLOS ONE}, author={El-Sabaawi, Rana W. and Kohler, Tyler J. and Zandona, Eugenia and Travis, Joseph and Marshall, Michael C. and Thomas, Steven A. and Reznick, David N. and Walsh, Matthew and Gilliam, James F. and Pringle, Catherine and et al.}, year={2012}, month={Mar} }
 @article{moslemi_snider_macneill_gilliam_flecker_2012, title={Impacts of an Invasive Snail (Tarebia granifera) on Nutrient Cycling in Tropical Streams: The Role of Riparian Deforestation in Trinidad, West Indies}, volume={7}, ISSN={["1932-6203"]}, DOI={10.1371/journal.pone.0038806}, abstractNote={Non-native species and habitat degradation are two major catalysts of environmental change and often occur simultaneously. In freshwater systems, degradation of adjacent terrestrial vegetation may facilitate introduced species by altering resource availability. Here we examine how the presence of intact riparian cover influences the impact of an invasive herbivorous snail, Tarebia granifera, on nitrogen (N) cycling in aquatic systems on the island of Trinidad. We quantified snail biomass, growth, and N excretion in locations where riparian vegetation was present or removed to determine how snail demographics and excretion were related to the condition of the riparian zone. In three Neotropical streams, we measured snail biomass and N excretion in open and closed canopy habitats to generate estimates of mass- and area-specific N excretion rates. Snail biomass was 2 to 8 times greater and areal N excretion rates ranged from 3 to 9 times greater in open canopy habitats. Snails foraging in open canopy habitat also had access to more abundant food resources and exhibited greater growth and mass-specific N excretion rates. Estimates of ecosystem N demand indicated that snail N excretion in fully closed, partially closed, and open canopy habitats supplied 2%, 11%, and 16% of integrated ecosystem N demand, respectively. We conclude that human-mediated riparian canopy loss can generate hotspots of snail biomass, growth, and N excretion along tropical stream networks, altering the impacts of an invasive snail on the biogeochemical cycling of N.}, number={6}, journal={PLOS ONE}, author={Moslemi, Jennifer M. and Snider, Sunny B. and MacNeill, Keeley and Gilliam, James F. and Flecker, Alexander S.}, year={2012}, month={Jun} }
 @article{lindstrom_blum_walter_gagne_gilliam_2012, title={Molecular and Morphological Evidence of Distinct Evolutionary Lineages of Awaous guamensis in Hawai'i and Guam}, ISSN={["1938-5110"]}, DOI={10.1643/ci-11-027}, abstractNote={Questions remain about the taxonomy and distribution of geographically widespread species in the circumtropical gobiid genus Awaous. Previous work that placed two species in synonymy on the basis of morphological characteristics effectively redefined the range of Awaous guamensis to include distant locations from Hawai'i and Guam to the islands of South-East Melanesia. Here we evaluate the synonymy of A. guamensis and A. stamineus through phylogeographic analysis of mitochondrial DNA sequence variation and morphological comparisons of Hawai'i and Guam populations. Phylogenetic assessments show clear separation of molecular characteristics, and morphological analyses illustrate statistically significant phenotypic differences indicating that the populations represent distinct evolutionary lineages. Based upon genetic, morphological, and geographic distributional differences, we recommend that Hawaiian populations be recognized as a distinct species, and reversion to the previous nomenclature of Awaous stamineus.}, number={2}, journal={COPEIA}, author={Lindstrom, Daniel P. and Blum, Michael J. and Walter, Ryan P. and Gagne, Roderick B. and Gilliam, James F.}, year={2012}, month={Jun}, pages={293–300} }
 @article{collazo_gilliam_miranda-castro_2010, title={Functional Response Models to Estimate Feeding Rates of Wading Birds}, volume={33}, ISSN={["1524-4695"]}, DOI={10.1675/063.033.0104}, abstractNote={Abstract. 
 Forager (predator) abundance may mediate feeding rates in wading birds. Yet, when modeled, feeding rates are typically derived from the purely prey-dependent Holling Type II (HoII) functional response model. Estimates of feeding rates are necessary to evaluate wading bird foraging strategies and their role in food webs; thus, models that incorporate predator dependence warrant consideration. Here, data collected in a mangrove swamp in Puerto Rico in 1994 were reanalyzed, reporting feeding rates for mixed-species flocks after comparing fits of the HoII model, as used in the original work, to the Beddington-DeAngelis (BD) and Crowley-Martin (CM) predator-dependent models. Model CM received most support (AIC c wi = 0.44), but models BD and HoII were plausible alternatives (&Dgr;AIC c ≤ 2). Results suggested that feeding rates were constrained by predator abundance. Reductions in rates were attributed to interference, which was consistent with the independently observed increase in aggression as flock size increased (P < 0.05). Substantial discrepancies between the CM and HoII models were possible depending on flock sizes used to model feeding rates. However, inferences derived from the HoII model, as used in the original work, were sound. While Holling's Type II and other purely prey-dependent models have fostered advances in wading bird foraging ecology, evaluating models that incorporate predator dependence could lead to a more adequate description of data and processes of interest. The mechanistic bases used to derive models used here lead to biologically interpretable results and advance understanding of wading bird foraging ecology.}, number={1}, journal={WATERBIRDS}, author={Collazo, Jaime A. and Gilliam, James F. and Miranda-Castro, Leopoldo}, year={2010}, month={Mar}, pages={33–40} }
 @article{walter_blum_snider_paterson_bentzen_lamphere_gilliam_2011, title={Isolation and differentiation of Rivulus hartii across Trinidad and neighboring islands}, volume={20}, ISSN={["1365-294X"]}, DOI={10.1111/j.1365-294x.2010.04968.x}, abstractNote={Diversification of freshwater fishes on islands is considered unlikely because the traits that enable successful colonization—specifically, broad salinity tolerances and the potential for oceanic dispersal—may also constrain post‐colonization genetic differentiation. Some secondary freshwater fish, however, exhibit pronounced genetic differentiation and geographic structure on islands, whereas others do not. It is unclear what conditions give rise to contrasting patterns of differentiation because few comparative reconstructions of population history have been carried out for insular freshwater fishes. In this study, we examined the phylogeography of Hart’s killifish (Rivulus hartii) across Trinidad, with reference to neighboring islands and northern South America, to test hypotheses of colonization and differentiation derived from comparable work on co‐occurring guppies (Poecilia reticulata). Geographic patterns of mitochondrial DNA haplotype variation and microsatellite genotype variation provide evidence of genetic differentiation of R. hartii among islands and across Trinidad. Our findings are largely consistent with patterns of geographically structured ancestry and admixture found in Trinidadian guppies, which suggests that both species share a history of colonization and differentiation and that post‐colonization diversification may be more common among members of insular freshwater fish assemblages than has been previously thought.}, number={3}, journal={MOLECULAR ECOLOGY}, author={Walter, Ryan P. and Blum, Michael J. and Snider, Sunny B. and Paterson, Ian G. and Bentzen, Paul and Lamphere, Brad A. and Gilliam, James F.}, year={2011}, month={Feb}, pages={601–618} }
 @article{howard_papich_felt_long_mckeon_bond_torreilles_luong_green_2010, title={The pharmacokinetics of enrofloxacin in adult African clawed frogs (Xenopus laevis)}, volume={49}, number={6}, journal={Journal of the American Association for Laboratory Animal Science}, author={Howard, A. M. and Papich, M. G. and Felt, S. A. and Long, C. T. and McKeon, G. P. and Bond, E. S. and Torreilles, S. L. and Luong, R. H. and Green, S. L.}, year={2010}, pages={800–804} }
 @article{snider_gilliam_2008, title={Movement ecology: Size-specific behavioral response of an invasive snail to food availability}, volume={89}, ISSN={["1939-9170"]}, DOI={10.1890/07-0715.1}, abstractNote={Immigration, emigration, migration, and redistribution describe processes that involve movement of individuals. These movements are an essential part of contemporary ecological models, and understanding how movement is affected by biotic and abiotic factors is important for effectively modeling ecological processes that depend on movement. We asked how phenotypic heterogeneity (body size) and environmental heterogeneity (food resource level) affect the movement behavior of an aquatic snail (Tarebia granifera), and whether including these phenotypic and environmental effects improves advection-diffusion models of movement. We postulated various elaborations of the basic advection diffusion model as a priori working hypotheses. To test our hypotheses we measured individual snail movements in experimental streams at high- and low-food resource treatments. Using these experimental movement data, we examined the dependency of model selection on resource level and body size using Akaike's Information Criterion (AIC). At low resources, large individuals moved faster than small individuals, producing a platykurtic movement distribution; including size dependency in the model improved model performance. In stark contrast, at high resources, individuals moved upstream together as a wave, and body size differences largely disappeared. The model selection exercise indicated that population heterogeneity is best described by the advection component of movement for this species, because the top-ranked model included size dependency in advection, but not diffusion. Also, all probable models included resource dependency. Thus population and environmental heterogeneities both influence individual movement behaviors and the population-level distribution kernels, and their interaction may drive variation in movement behaviors in terms of both advection rates and diffusion rates. A behaviorally informed modeling framework will integrate the sentient response of individuals in terms of movement and enhance our ability to accurately model ecological processes that depend on animal movement.}, number={7}, journal={ECOLOGY}, author={Snider, Sunny B. and Gilliam, James F.}, year={2008}, month={Jul}, pages={1961–1971} }
 @article{fraser_gilliam_albanese_snider_2006, title={Effects of temporal patterning of predation threat on movement of a stream fish: evaluating an intermediate threat hypothesis}, volume={76}, ISSN={["0378-1909"]}, DOI={10.1007/s10641-006-9004-9}, number={1}, journal={ENVIRONMENTAL BIOLOGY OF FISHES}, author={Fraser, Douglas F. and Gilliam, James F. and Albanese, Brett W. and Snider, Sunny B.}, year={2006}, month={May}, pages={25–35} }
 @article{skalski_picha_gilliam_borski_2005, title={Variable intake, compensatory growth, and increased growth efficiency in fish: Models and mechanisms}, volume={86}, ISSN={["1939-9170"]}, DOI={10.1890/04-0896}, abstractNote={Resources fluctuate in space and time, and animals routinely experience temporally varying opportunities for resource intake, and variation in intake itself. We investigate consequences of such variation in intake on growth and growth efficiency (growth per unit intake) in juvenile hybrid striped bass. We observed, after statistically accounting for the effects of total consumption and initial body size, that individuals re- ceiving a low ration followed by a higher ration (the fluctuating ration) grew faster than individuals receiving a temporally constant ration (the normal ration). To interpret this increase in growth efficiency, we consider a set of alternative models representing different physiological hypotheses of the growth process. Using a simple growth model, an analytical result shows that the fluctuating ration as typically applied in experiments (a low ration followed by a high ration), independent of any change in physiology, increases growth efficiency relative to individuals on the normal ration. Growth efficiency increases because cumulative maintenance costs are lower for individuals that stay small initially and then grow rapidly in comparison to individuals that grow steadily. Further, a statistical analysis of alternative models inferred that fish receiving a variable ration show higher assimilation and/or conversion efficiencies of food and lower mass-specific maintenance costs. Our analysis suggests that the lower cumulative maintenance costs incurred over a time interval with low consumption followed by high consumption act in association with higher assim- ilation-conversion efficiencies, and lower overall mass-specific maintenance costs to in- crease growth efficiency in hybrid striped bass.}, number={6}, journal={ECOLOGY}, author={Skalski, GT and Picha, ME and Gilliam, JF and Borski, RJ}, year={2005}, month={Jun}, pages={1452–1462} }
 @article{fraser_gilliam_akkara_albanese_snider_2004, title={Night feeding by guppies under predator release: Effects on growth and daytime courtship}, volume={85}, ISSN={["0012-9658"]}, DOI={10.1890/03-3023}, abstractNote={The nonlethal effects of predation threat can be pervasive but are also easily overlooked. We investigated effects of predation threat on feeding by guppies (Poecilia reticulata), and how threat-induced temporal shifts in feeding activity affect reproductive behavior and growth. Contrary to the view of the guppy as a “diurnal” species, our observations revealed that guppies free from severe predation threat expand their foraging into the nocturnal period. We found such nocturnal foraging to be as profitable as diurnal foraging, and guppies under threat incurred a substantial growth penalty when predators inhibited night feeding. Denial of night feeding also decreased daytime courtship by males, facultatively duplicating a classical observation comparing courtship intensity in contrasting predator regimes, but providing a novel mechanism for the effect. Our findings support the view that evaluations of predator effects on life histories should consider potential predator-caused alterations in size-specific...}, number={2}, journal={ECOLOGY}, author={Fraser, DF and Gilliam, JF and Akkara, JT and Albanese, BW and Snider, SB}, year={2004}, month={Feb}, pages={312–319} }
 @article{skalski_gilliam_2003, title={A diffusion-based theory of organism dispersal in heterogeneous populations}, volume={161}, ISSN={["1537-5323"]}, DOI={10.1086/367592}, abstractNote={We develop a general theory of organism movement in heterogeneous populations that can explain the leptokurtic movement distributions commonly measured in nature. We describe population heterogeneity in a state‐structured framework, employing advection‐diffusion as the fundamental movement process of individuals occupying different movement states. Our general analysis shows that population heterogeneity in movement behavior can be defined as the existence of different movement states and among‐individual variability in the time individuals spend in these states. A presentation of moment‐based metrics of movement illustrates the role of these attributes in general dispersal processes. We also present a special case of the general theory: a model population composed of individuals occupying one of two movement states with linear transitions, or exchange, between the two states. This two‐state “exchange model” can be viewed as a correlated random walk and provides a generalization of the telegraph equation. By exploiting the main result of our general analysis, we characterize the exchange model by deriving moment‐based metrics of its movement process and identifying an analytical representation of the model’s time‐dependent solution. Our results provide general and specific theoretical explanations for empirical patterns in organism movement; the results also provide conceptual and analytical bases for extending diffusion‐based dispersal theory in several directions, thereby facilitating mechanistic links between individual behavior and spatial population dynamics.}, number={3}, journal={AMERICAN NATURALIST}, author={Skalski, GT and Gilliam, JF}, year={2003}, month={Mar}, pages={441–458} }
 @article{skalski_gilliam_2002, title={Feeding under predation hazard: Testing models of adaptive behavior with stream fish}, volume={160}, ISSN={["1537-5323"]}, DOI={10.1086/341012}, abstractNote={Many empirical studies support the premise that animals consider both the benefits of feeding and the cost of mortality when making behavioral decisions, and many theoretical studies predict animal behavior in the presence of a feeding‐mortality trade‐off. However, empirical work is lacking in studies that quantitatively assess alternative models. Using data from two sets of behavioral experiments examining stream minnows (bluehead chubs) foraging in the presence of sunfish predators (green sunfish), we assess, via statistical model fitting, the utility of four basic optimization models of foraging behavior. Our analysis of feeding and mortality of the minnows indicates that mortality is incurred so as to feed above maintenance requirements, that feeding rate is suppressed in response to the presence of predators, and that the balance of feeding against mortality can be estimated using a life‐history parameter θ, interpreted theoretically as the marginal rate of substitution of mortality rate for growth rate. Our results indicate that both body size and age are probably involved in determining the value of θ, and we suggest that future studies should focus on estimating and understanding this parameter.}, number={2}, journal={AMERICAN NATURALIST}, author={Skalski, GT and Gilliam, JF}, year={2002}, month={Aug}, pages={158–172} }
 @article{fraser_gilliam_daley_le_skalski_2001, title={Explaining leptokurtic movement distributions: Intrapopulation variation in boldness and exploration}, volume={158}, ISSN={["1537-5323"]}, DOI={10.1086/321307}, abstractNote={Leptokurtic distributions of movement distances observed in field‐release studies, in which some individuals move long distances while most remain at or near their release point, are a common feature of mobile animals. However, because leptokurtosis is predicted to be transient in homogeneous populations, persistent leptokurtosis suggests a population heterogeneity. We found evidence for a heterogeneity that may generate persistent leptokurtosis. We tested individuals of the Trinidad killifish Rivulus hartii for boldness in a tank test and released them back into their native stream. Boldness in the tank test predicted distance moved in the field releases, even after effects of size and sex were removed. Further, data from a 19‐mo mark‐recapture study showed that individual growth correlated positively with movement in a predator‐threatened river zone where the Rivulus population is spatially fragmented and dispersal is likely to be a hazardous activity. In contrast, no such correlation existed in a predator‐absent zone where the population is unfragmented. These results show that a behavioral trait, not discernible from body size or sex, contributes to dispersal and that a component of fitness of surviving “dispersers” is elevated above that of “stayers,” a fundamental assumption or prediction of many models of the evolution of dispersal through hazardous habitat.}, number={2}, journal={AMERICAN NATURALIST}, author={Fraser, DF and Gilliam, JF and Daley, MJ and Le, AN and Skalski, GT}, year={2001}, month={Aug}, pages={124–135} }
 @article{skalski_gilliam_2001, title={Functional responses with predator interference: viable alternatives to the Holling Type II model}, volume={82}, DOI={10.2307/2679836}, abstractNote={A predator's per capita feeding rate on prey, or its functional response, provides a foundation for predator–prey theory. Since 1959, Holling's prey-dependent Type II functional response, a model that is a function of prey abundance only, has served as the basis for a large literature on predator–prey theory. We present statistical evidence from 19 predator–prey systems that three predator-dependent functional responses (Beddington-DeAngelis, Crowley-Martin, and Hassell-Varley), i.e., models that are functions of both prey and predator abundance because of predator interference, can provide better descriptions of predator feeding over a range of predator–prey abundances. No single functional response best describes all of the data sets. Given these functional forms, we suggest use of the Beddington-DeAngelis or Hassell-Varley model when predator feeding rate becomes independent of predator density at high prey density and use of the Crowley-Martin model when predator feeding rate is decreased by higher predator density even when prey density is high.}, number={11}, journal={Ecology (Brooklyn, New York, N.Y.)}, author={Skalski, G. T. and Gilliam, J. F.}, year={2001}, pages={3083–3092} }
 @article{gilliam_fraser_2001, title={Movement in corridors: Enhancement by predation threat, disturbance, and habitat structure}, volume={82}, ISSN={["1939-9170"]}, DOI={10.2307/2680101}, abstractNote={Movement by stream fish is known to be strongly influenced by abiotic factors such as floods and temperature, but roles of biotic factors, such as predation threat, and interactions of abiotic and biotic factors are less clear. Predation threat is known to fragment populations of killifish, Rivulus hartii, in Trinidad rivers by rendering habitat inhospitable. We asked whether such spatial fragmentation was accompanied by reduced movement by fish in the predator-occupied zone of a river, relative to a zone free of the strong piscivore, Hoplias malabaricus, that causes the fragmentation. We used a 19-mo marking study in a river with a predator barrier, field experiments in the river, and mesocosms to evaluate four hypotheses: (1) the predator reduces prey movement in the river; (2) for the special case of prey leaving refugia, the predator increases movement; (3) movement positively correlates with water level in the predator's presence; and (4) complex physical structure in hazardous habitat promotes prey movement. We marked 1467 Rivulus in the natural study areas and had 1015 recaptures. Contrary to Hypothesis 1 but in support of Hypothesis 2, prey showed greater movement along the river in the presence of the predator, regardless of whether the fish resided in a refuge at its previous capture. An experiment with introduced fish confirmed the findings that movement was elevated in the predator's presence. Effects of an abiotic factor (water level, Hypothesis 3) and a phenotypic trait (body size) depended upon whether the predator was present: movement was independent of water level and body size in the absence of the predator, but positively related to both variables in the predator's presence. Emigration from the river to tributaries was also independent of body size in the predator's absence, but positively size-dependent in the predator's presence. Complex physical structure (Hypothesis 4), in the form of cobble added to experimental pools, enhanced the transit of fish through hazardous pools. This study shows that spatial fragmentation does not necessarily imply that movement between fragments will be impeded (dynamical fragmentation). Rather, it is possible that movement among spatial fragments may be enhanced by the same factor, predation threat, that produced the spatial fragmentation in the first place. Because of the context-dependent effects of an abiotic factor (water level) and a phenotypic variable (body size) on movement, the study also emphasizes the need to clarify the exact role of predation as an agent promoting or retarding movement, and it suggests a need for incorporating such parameters into models of movement and metapopulation dynamics.}, number={1}, journal={ECOLOGY}, author={Gilliam, JF and Fraser, DF}, year={2001}, month={Jan}, pages={258–273} }
 @article{skalski_gilliam_2000, title={Modeling diffusive spread in a heterogeneous population: A movement study with stream fish}, volume={81}, ISSN={["1939-9170"]}, DOI={10.2307/177317}, abstractNote={Using a mark–recapture technique in a small temperate stream, we described the movement of four fish species over a five-month period and developed a mathematical model that described the observed movement patterns. The movement distributions were generally leptokurtic, and two of the four species demonstrated some degree of upstream bias. There was little difference in movement among species or through time. There were no temporal correlations in probability of movement, movement direction, or distance moved. The spatial spread of the most abundant species, bluehead chubs, over a four-month period was characterized by upstream bias, diffusion-like spread, and persistent leptokurtosis. Bluehead chubs demonstrated complex relationships between probability of movement and size and growth, while creek chubs showed only an effect of size on probability of movement. Further, growth of individual bluehead chubs was correlated through time. These empirical results suggest the hypothesis that heterogeneity in phenotypic attributes, such as size and growth, is related to heterogeneity in movement behavior. A diffusion–advection model of bluehead chub movement, structured with two subgroups that dispersed at different rates ("fast fish" and "slow fish"), was parameterized and validated with the field data. This model with heterogeneity in movement rates generated the leptokurtic pattern observed in the field data, in contrast to the classic diffusion model without population heterogeneity, which produces a normal distribution. The results from this work suggest that heterogeneity in fitness-influencing attributes such as size and growth could explain heterogeneity in individual-level movement behavior and might underlie the leptokurtic patterns that have been observed at the population level in numerous field studies.}, number={6}, journal={ECOLOGY}, author={Skalski, GT and Gilliam, JF}, year={2000}, month={Jun}, pages={1685–1700} }
 @article{fraser_gilliam_macgowan_arcaro_guillozet_1999, title={Habitat quality in a hostile river corridor}, volume={80}, DOI={10.2307/176638}, abstractNote={EcologyVolume 80, Issue 2 p. 597-607 Article HABITAT QUALITY IN A HOSTILE RIVER CORRIDOR Douglas F. Fraser, Douglas F. Fraser Department of Biology, Siena College, Loudonville, New York 12211 USA E-mail: fraser@siena.eduSearch for more papers by this authorJames F. Gilliam, James F. Gilliam Department of Zoology, North Carolina State University, Raleigh, North Carolina 27695-7617 USASearch for more papers by this authorMelissa P. MacGowan, Melissa P. MacGowan Department of Biology, Siena College, Loudonville, New York 12211 USASearch for more papers by this authorCanyon M. Arcaro, Canyon M. Arcaro Department of Biology, Siena College, Loudonville, New York 12211 USASearch for more papers by this authorPeter H. Guillozet, Peter H. Guillozet Department of Zoology, North Carolina State University, Raleigh, North Carolina 27695-7617 USASearch for more papers by this author Douglas F. Fraser, Douglas F. Fraser Department of Biology, Siena College, Loudonville, New York 12211 USA E-mail: fraser@siena.eduSearch for more papers by this authorJames F. Gilliam, James F. Gilliam Department of Zoology, North Carolina State University, Raleigh, North Carolina 27695-7617 USASearch for more papers by this authorMelissa P. MacGowan, Melissa P. MacGowan Department of Biology, Siena College, Loudonville, New York 12211 USASearch for more papers by this authorCanyon M. Arcaro, Canyon M. Arcaro Department of Biology, Siena College, Loudonville, New York 12211 USASearch for more papers by this authorPeter H. Guillozet, Peter H. Guillozet Department of Zoology, North Carolina State University, Raleigh, North Carolina 27695-7617 USASearch for more papers by this author First published: 01 March 1999 https://doi.org/10.1890/0012-9658(1999)080[0597:HQIAHR]2.0.CO;2Citations: 55 Read the full textAboutPDF ToolsRequest permissionExport citationAdd to favoritesTrack citation ShareShare Give accessShare full text accessShare full-text accessPlease review our Terms and Conditions of Use and check box below to share full-text version of article.I have read and accept the Wiley Online Library Terms and Conditions of UseShareable LinkUse the link below to share a full-text version of this article with your friends and colleagues. Learn more.Copy URL Share a linkShare onFacebookTwitterLinkedInRedditWechat Abstract Stream fish often occur in tributaries at high densities, and dispersal between tributaries must occur through the intervening river, whose attributes may differ from those of the tributaries. In Trinidad, tributaries of the Guanapo River have high densities of a killifish, Rivulus hartii, but the river also contains a strong piscivore that may affect the quality of the river as a movement corridor linking the adjoining tributaries. We hypothesized that R. hartii in the river, where they are scarce and confined to margins, would show stress as predicted for an animal in transit through a hostile corridor. We predicted that river fish would take in less food, grow more slowly, and contain fewer mature oocytes than tributary fish. We tested these predictions by comparing R. hartii from paired tributary and river sites for food intake, growth, and oocyte counts. We also asked whether R. hartii could spawn successfully in shallow water, such as at the river margins. To determine whether the river would satisfy criteria for its use as a movement corridor (movement along the river and movement in and out of tributaries), we marked 709 R. hartii in a 500-m stretch of river and two adjoining tributaries and recaptured them on seven sampling dates over a 15-mo period. Contrary to our predictions, R. hartii in the river showed no stress in the form of reduced food intake, growth, or suppressed reproductive output. Instead, we detected no difference in food intake of R. hartii sampled from paired tributary–river sites, and river R. hartii displayed a greater growth rate and contained more mature oocytes than did their tributary counterparts. Laboratory and field studies also revealed that R. hartii can spawn viable eggs in shallow water that does not cover their bodies. The movement study confirmed that the river has a conduit function for communication between tributaries, but the river also has a habitat function, as it contains resident individuals that grow and reproduce in the corridor. This means that movement of alleles and recolonization of local extinctions can occur via offspring of dispersers, rather than require successful movement of individuals directly between tributaries. Citing Literature Volume80, Issue2March 1999Pages 597-607 RelatedInformation}, number={2}, journal={Ecology (Brooklyn, New York, N.Y.)}, author={Fraser, D. F. and Gilliam, J. F. and MacGowan, M. P. and Arcaro, C. M. and Guillozet, P. H.}, year={1999}, pages={597–607} }