Variation In Microhabitat Use Research Articles

Will climatic changes affect the Vietnamese crocodile lizard? Seasonal variation in microclimate and activity pattern of Shinisaurus crocodilurus vietnamensis

Abstract Climate change is considered to negatively affect vertebrate biodiversity. Lizards in tropical regions are considered particularly vulnerable due to their narrow temperature tolerances. The crocodile lizard Shinisaurus crocodilurus, an ecologically specialized semiaquatic species, is under the risk of extinction due to habitat loss and overharvesting. It is only found in isolated relict populations in southern China and northern Vietnam. Data on the thermal niche of the species are crucial to assess its vulnerability to climatic changes. We developed a backpack system with temperature data loggers for S. crocodilurus in order to monitor the lizard’s temperature preferences in its natural habitat in Vietnam. We found that S. crocodilurus vietnamensis preferred a mean ambient temperature range of 24 ± 1°C (min-max: 22-31°C) at natural habitat sites, a far lower temperature amplitude compared to the recorded ambient temperature range at habitat sites. In its natural habitat, S. crocodilurus vietnamensis avoided in particular high temperatures, indicating the importance of constantly cool streams and intact vegetation for the provision of shade and shelter. We further provide first insights into the seasonal variation in microhabitat use and activity of S. crocodilurus vietnamensis based on data from individuals kept in outdoor enclosures under natural climatic conditions in Vietnam, collected daily over a period of eight months. Our results aim to aid further conservation measures for the species, such as the identification and protection of core habitat sites and sites for restocking, as well as to adjust and improve conservation breeding programs for the species.

Metabolic Rate Interacts with Resource Availability to Determine Individual Variation in Microhabitat Use in the Wild.

Ecological pressures such as competition can lead individuals within a population to partition resources or habitats, but the underlying intrinsic mechanisms that determine an individual's resource use are not well understood. Here we show that an individual's own energy demand and associated competitive ability influence its resource use, but only when food is more limiting. We tested whether intraspecific variation in metabolic rate leads to microhabitat partitioning among juvenile Atlantic salmon (Salmo salar) in natural streams subjected to manipulated nutrient levels and subsequent per capita food availability. We found that individual salmon from families with a higher baseline (standard) metabolic rate (which is associated with greater competitive ability) tended to occupy faster-flowing water, but only in streams with lower per capita food availability. Faster-flowing microhabitats yield more food, but high metabolic rate fish only benefited from faster growth in streams with high food levels, presumably because in low-food environments the cost of a high metabolism offsets the benefits of acquiring a productive microhabitat. The benefits of a given metabolic rate were thus context dependent. These results demonstrate that intraspecific variation in metabolic rate can interact with resource availability to determine the spatial structuring of wild populations.

Reproductive activity, microhabitat use, and calling sites of Pristimantis bacchus (Anura: Craugastoridae)

Abstract Pristimantis bacchus is an endangered terrestrial frog, endemic to cloud forests of the northern part of the Cordillera Oriental in the Colombian Andes. The knowledge of its reproductive biology and microhabitat use can offer important information for future conservation programs. We evaluated the reproductive activity and microhabitat use for both sexes, and selection of calling sites by males during rainy and dry seasons. Individuals of all reproductive conditions were observed throughout the sampled months; however, we observed a higher abundance of frogs during the first rainy season, after the driest months of the year. Thus, this population seems to have continuous reproductive activity, with an apparent peak at the onset of the first rainy season of the year. There were differences in the microhabitat use between sexes, between adults and juveniles, and between non-reproductive and reproductive females. Males use a wider variety of substrates at higher perches, while females were mainly found on leaf litter and over leaves at low heights; however, ovigerous females mostly occupied substrates above 120 cm. Juveniles were less abundant than adults, and occupy low substrates, mostly at forest litter. Two selection models evaluated the preference for calling sites, related to physiological requirements of humidity and for vocal sound dispersion. Males preferred to vocalize on perches at heights among 41-120 cm and with a vegetal structure that maintains high humidity, avoiding desiccation, and reducing exposure to predators. Therefore, intrapopulation variation in microhabitat use in this species is related to age, sex, reproductive condition, and physiological requirements.

Coldwater Periods in Warmwater Streams: Microhabitat Shifts from Autumn to Winter by Smallmouth Bass

AbstractSeasonal and life stage variation in microhabitat use is an important driver of fish survival and bioenergetics, but knowledge of microhabitat selection during colder periods is generally lacking in warmwater streams. Our objective was to examine changes in microhabitat selection by age‐0 (TL ≤ 85 mm) and age‐1+ (TL > 85 mm) Smallmouth Bass Micropterus dolomieu from autumn to winter in streams of the southwest Ozark Highlands ecoregion. We examined microhabitat selection (depth, velocity, substrate, cover, and temperature) during autumn 2017 (Spavinaw Creek) and winter 2018 (Spavinaw and Spring creeks). During autumn and winter, age‐0 fish selected intermediate depths of approximately 1 m, whereas age‐1+ fish selected the deepest available habitat. Water depth selection was similar across seasons for both life stages. Both age‐0 and age‐1+ bass selected areas of zero velocity, increasing substrate size, instream cover, and warmwater patches in autumn. Velocity selection differed between autumn and winter with both life stages showing stronger selection of low velocity patches (0.1–0.3 m/s) during winter. Both life stages shifted to having no substrate selection during winter. Age‐1+ bass were more likely than age‐0 bass to use cover during autumn, but this relationship shifted in winter to the age‐0 cohort increasing their selection of cover and the age‐1+ cohort decreasing their selection. Both age‐0 and age‐1+ bass selected relatively warmer habitats during autumn, but not winter. Collectively, our results highlight both seasonal and life stage variation in Smallmouth Bass microhabitat selection. As our understanding of habitat selection across seasons develops, the management of Smallmouth Bass will undoubtedly improve. Changing environmental conditions over time may influence available habitat as well as the timing of seasonal shifts across a range of spatial and temporal scales, including microhabitat patches.

Interspecific Variation in Seasonal Migration and Brumation Behavior in Two Closely Related Species of Treefrogs

Most amphibians migrate between flooded habitats for breeding and dry habitats for non-breeding activities, however, differences in closely related species may highlight divergent evolutionary histories. Through field surveys, Harmonic Direction Finder tracking and laboratory behavioural experiments during the wintering season, we demonstrated differences in seasonal migration and hibernation habitats between Dryophytes suweonensis and D. japonicus. We found that D. japonicus migrated towards forests for overwintering and then back to rice paddies for breeding in spring. By contrast, D. suweonensis was found to hibernate buried in the vicinity of rice paddies, its breeding habitat. We also found that the difference in migrating behaviour matched with variation in microhabitat use during brumation and hibernation between the two species. Our findings highlight different ecological requirements between the two species, which may result from their segregated evolutionary histories, with speciation potentially linked to species use of a new breeding habitat. Additionally, the use of rice paddies for both breeding and hibernation may contribute to the endangered status of D. suweonensis because of the degradation of hibernation sites in winter.

Microhabitat estimation of an imperiled headwater fish, the Yazoo darter (Etheostoma raneyi), in coastal plain streams

Headwater fishes in the southeastern United States make up much of the fish biodiversity of the region yet many are imperiled. Despite this, the specific habitat requirements of imperiled headwater fishes in lowland Coastal Plain streams have rarely been quantified. Using data collected over three years of seasonal sampling we provide estimates of the microhabitat requirements of the imperiled Yazoo darter (Etheostoma raneyi Suttkus and Bart), a small benthic insectivore. Our results indicate that the species is a microhabitat specialist and that optimum microhabitat within degraded contemporary streams consists of a narrow range of water depths (about 20–30 cm), current velocity ≥ 0.25 m·s−1, complex stable debris piles, rooted macrophytes, and likely coarse substrate. No pronounced or generalized seasonal shifts in microhabitat use occurs, and no evidence exists for intraspecific partitioning of microhabitat. Though stable and complex instream cover is one of the most important variables explaining variation in microhabitat use by Yazoo darters, such cover is rare in the degraded streams within the range of the species. Current conservation classifications of the Yazoo darter by governmental agencies and nongovernmental organizations as well as associated management plans that are based on the assumption that Yazoo darters are habitat generalists should be reviewed in recognition of the increased risk of decline because Yazoo darters are microhabitat specialists. These considerations should also be extended to other closely related imperiled species of snubnose darters.

Temporal Variation in Structural Microhabitat Use ofPhelsumaGeckos in Mauritius

Abstract Microhabitat use is an important aspect of an organism's niche, often influencing both intra- and interspecific interactions such as competition. To reduce competitive interactions, species may shift their behavior when in sympatry to gain greater access to resources, resulting in patterns of habitat partitioning. Previous studies have described structural microhabitat partitioning in Phelsuma geckos with the likely cause being interference competition. Such interference competition also may lead to temporal microhabitat partitioning. We investigated the presence of temporal habitat partitioning in Phelsuma geckos from Mauritius and the relation of partitioning to competition. We found temporal variation in microhabitat use for Mauritian Phelsuma. However, this variation was not clearly associated with the presence of other focal Phelsuma species, suggesting competition may not be responsible for the observed pattern. Temporal habitat partitioning in Mauritian Phelsuma geckos may be attributable ...

The tadpoles of the neotropical Scinax catharinae group (Anura, Hylidae): Ecomorphology and descriptions of two new forms

Herein we provide novel data on the external morphological features and natural history of the tadpoles of Scinax canastrensis and Scinax carnevallii, two poorly known tree frog species occurring in southeastern Brazil. Both species share characteristics with all other species of the Scinax catharinae group, including oral discs not emarginated with the posterior margin concave when closed, many submarginal papillae laterally, circular nostrils, and vent tubes reaching the ventral fin margin. Landmark-based geometric morphometrics applied to 16 species of the S. catharinae group indicate that their tadpoles have substantial variation in body shape, yet with some overlap among species. Although the lentic/lotic habitat categorization was not sufficient for explaining the complex patterns of morphospace occupancy by tadpoles of S. catharinae group, some well-established ecomorphological relationships were recovered, such as that for suctorial and pond-type guilds. Moreover, the morphological diversity in shape may also reflect interspecific variation in microhabitat use, other contemporary factors (e.g., other abiotic habitat components and/or biological interactions) and evolutionary relationships.

Local variations in microhabitat use by Stegastes fuscus (Cuvier, 1830) (Teleostei: Pomacentridae) in a tropical reef of Brazil

Due to their widespread abundance and territorial habits, damselfishes play central roles in reefs worldwide, but the extent to which they modify the reef's substrate varies both amongst and within species. The present study evaluated microhabitat preferences and the role of the common damselfish Stegastes fuscus (Cuvier, 1830) (Teleostei: Pomacentridae) as a benthic community modifier in a tropical algal-dominated reef. We employed video survey techniques to assess fish density and microhabitat use and, additionally, the biomass of sessile components were compared inside and immediately outside algal farms of S. fuscus. Individuals showed pronounced microhabitat preference, but with prominent local (i.e. small-scale) variations in benthic cover. These local variations are reported for the first time and were due to individuals defending one of two contrasting microhabitats (i.e. turf-dominated or Palythoa caribaeorum-dominated). Further, significant differences in the biomass of sessile organisms were observed within algal farms suggesting that S. fuscus plays a keystone role in the benthic community of the reef. The implications of the prominent local variation in microhabitat use are discussed and strongly illustrate the behavioral plasticity of this damselfish.

The relationship between microhabitat use, allometry and functional variation in the eyes of Hawaiian Megalagrion damselflies

Summary The evolution of visual systems is guided by visual requirements imposed by the environment, the size of the animal's eyes, and physical limitations imposed by the resolution‐sensitivity trade‐off. Given a particular eye surface area, resolution and sensitivity cannot be simultaneously maximized: gains in resolution, the ability of the eye to detect detail, will come at the cost of sensitivity, the ability to capture photons, and vice versa, without an increase to eye size. How this constraint interacts with ecology and whether it allows the fine‐tuning of the visual system to smaller scale habitat heterogeneity remains an understudied question in visual ecology. Here, we use closely‐related species of damselflies in the Hawaiian genus Megalagrion which differ in ecology to test whether variation in the resolution‐sensitivity trade‐off is the evolutionary result of scaling or differences in microhabitat use. We use regression analyses and phylogenetic comparative methods to examine the effects of size and microhabitat use on traits related to light sensitivity and visual resolution. We find that eye size is tightly associated with body size in these damselflies, but other visual morphology traits related to light sensitivity and resolution are associated with microhabitat type. Furthermore, size and morphology relationships vary across microhabitats, and performance related to resolution tends to be more conserved than to variation in light sensitivity. Additionally, smaller species in visually challenging microhabitats have more regionalized eyes than species with larger eyes in open, well‐lit areas. Thus, regionalization of the eye allows a decoupling of size and morphology/performance so that even small insect species can exploit visually challenging habitats. These results suggest that variation in visual performance results from changes in eye geometry as well as size. These morphological changes are likely adaptive to differences in microhabitat, indicating that variation in microhabitat use, even at small scales, can play an important role in the evolution of visual systems.

Topographic microclimates drive microhabitat associations at the range margin of a butterfly

The habitat associations of individuals underpin the dynamics of species distributions. Broad‐scale gradients in climate can alter habitat associations across species’ geographic ranges, but topographic heterogeneity creates local microclimates which could generate variation in habitat use at finer spatial scales. We examined the selection of microhabitats for egg‐laying by populations of a thermally‐constrained butterfly, the skipper Hesperia comma, across 16 sites with different regional temperatures and topographic microclimates. Using models of thermal microclimate, we examined how the association between eggs and warm bare ground microhabitats varied with ambient temperature, and predicted bare ground associations in 287 existing H. comma populations, to investigate the relative impacts of regional temperatures and topographic microclimates on microhabitat use. Eggs were most strongly associated with bare ground in relatively cool sites, indicating climate‐driven changes in microhabitat use. The majority of temperature variation between study sites was attributable to topographic microclimates rather than regional temperature differences, such that changes in microhabitat associations occurred principally between north‐ and south‐facing slopes within the same region. Predicted microhabitat associations across the UK distribution of H. comma showed that, due to the large temperature differences generated by topography, most of the between‐population variation in microhabitat use occurs locally within 5 km grid squares, with a smaller proportion occurring at a regional level between 5 km squares. Our findings show how microclimatic variation generated by topography alters the habitat associations of populations at fine spatial scales, suggesting that microclimate‐driven changes in habitat suitability could shape species’ distribution dynamics and their responses to environmental change.

Variation in microhabitat use of the threatened spotfin chub (Erimonax monachus) among stream sites and seasons

Abstract – The spotfin chub Erimonax monachus is a rare cyprinid fish endemic to the Tennessee River drainage, and it is federally listed as threatened in the USA. Microhabitat use of spotfin chubs was studied via stream snorkelling in the Emory River watershed, Tennessee, one of the last remaining populations of this species. We used a Bayesian generalised linear mixed model to evaluate microhabitat covariates related to the presence/absence of spotfin chubs among eight stream sites across three seasons (early summer, late summer and fall). In general, spotfin chubs were more likely to be present in microhabitats characterised by boulder/bedrock substrates, medium to high velocity, and medium depth (typical of the run habitat). However, the patterns were not necessarily consistent among seasons or stream sites, due partly to interactions between microhabitat and macrohabitat covariates. Specifically, spotfin chubs were more selective of bedrock and boulder substrate at smaller stream sites where they were less abundant, and they were more selective of higher velocity at warmer stream temperatures (early and late summer). Our data indicate that spotfin chubs may exhibit flexible microhabitat use to some extent, and their microhabitat use may differ by macrohabitat characteristics such as stream size and water temperature. This study provided a refined understanding of microhabitat use of spotfin chubs and suggests that effective conservation of this declining species should identify and protect available suitable habitat across space and time.

Niche Occupancy and the Relative Role of Micro-Habitat and Diet in Resource Partitioning Among Pond Dwelling Tadpoles

ABSTRACT. We determined microhabitat and diet niche for tadpoles from two ponds in an agricultural landscape. Additionally, we verified the intraspecific variation in resource use, and if diet and microhabitat use were correlated. Tadpoles found in the two ponds differed in microhabitat use, because in the larger pond they explored deeper places far from the margin. There were three groups with high microhabitat niche overlap. In both ponds, plant cover was the best descriptor to explain interspecific variation in microhabitat use. Tadpoles of all species ingested mainly Bacillariophyceae and Trachellomonas however the diet differed intraspecifically in the species from the two ponds. Ten items in the temporary pond and 15 items in the permanent one were ingested by all species; however, the relative abundance of each item differed. Diet similarity was not correlated to similarity in microhabitat use. In this study, diet was as important as microhabitat use to explain resource partitioning.

Lack of phylogenetic signal in the variation in anuran microhabitat use in southeastern Brazil

Microhabitat use is an important component of anuran behavior in both the tadpole and the adult stages. It is potentially influenced by phylogeny and extant ecological factors acting as selective pressures, such as predation, competition, or physical habitat properties. We aimed to test whether patterns of microhabitat use vary among species, habitats and sites, and how much of this variation can be explained by phylogenetic relatedness. We collected data on microhabitat use at five different sites, where we obtained a total of 4,230 records of individual tadpoles of 34 species in 15 genera and 7 families, and a total of 1,163 records of adult individuals of 39 species in 16 genera and 8 families. Mantel tests conducted to relate species dissimilarities in microhabitat use and phylogenetic relatedness indicated a weak but significant relationship for adult anurans, and no relationship for tadpoles. Our results suggest that microhabitat use is a plastic and variable trait, overcoming phylogenetic signal in tadpoles. In adult anurans, very little of the variation in microhabitat use can be explained by phylogenetic relatedness. Microhabitat use is not a good predictor of phylogeny, but it may be a very interesting subject to study natural selection and adaptation.

What drives variation in habitat use by Anolis lizards: habitat availability or selectivity?

Geographic variation in habitat availability may drive geographic variation in a species’ habitat use; alternatively, species adapted to particular habitat characteristics may use a habitat regardless of its availability within an environment. In this study, we investigated habitat use of two sympatric species of Anolis lizards that are morphologically specialized to use different microhabitats. We examined variation in microhabitat use and availability among four distinct forest types. In each forest type, we quantified available microhabitats (i.e., perch diameter, angle of inclination, and visibility), as well as microhabitats actually used by each species. We found that species consistently differed in microhabitat use, corresponding to each species’ morphological specializations. However, microhabitat use of both species varied among sites. This variation in Anolis gundlachi Peters, 1876 reflected differences in microhabitat availability, while the variation in Anolis krugi Peters, 1876 resulted from differential microhabitat selectivity. These results indicate that both habitat availability and habitat preferences must be examined in multiple localities for a species to understand the causes of variation in its habitat use.

THE NORTHERN FLYING SQUIRREL AS AN INDICATOR SPECIES OF TEMPERATE RAIN FOREST: TEST OF AN HYPOTHESIS

Management indicator species (MIS) often are selected because their life history and demographics are thought to reflect a suite of ecosystem conditions that are too difficult or costly to measure directly. The northern flying squirrel (Glaucomys sabrinus) has been proposed as an MIS of temperate rain forest of southeastern Alaska based on previous studies in the Pacific Northwest that demonstrated its habitat is multi‐factorial, i.e., an emergent property of old‐growth forest. We evaluated the suitability of flying squirrels as MIS in temperate rain forests of Alaska by modeling seasonal (spring, autumn) microhabitat use with stepwise logistic regression (SLR) using either individual habitat variables (n = 26) or multivariate habitat “factors,” which were linear combinations of individual habitat variables generated from factor analysis. We compared the efficacy of single variable vs. multivariate factor models in explaining variation in microhabitat use to test the hypothesis that the habitat of flying squirrels in southeastern Alaska was an emergent property of old‐growth rain forest. The underlying premise was that if factors were more thorough in explaining microhabitat use, the habitat of flying squirrels was multifactorial; that is, it consisted of multiple late‐seral forest attributes occurring coincidentally at usable spatial scales (e.g., home range). SLR models with multivariate factors performed poorer in predicting capture sites than models of individual habitat variables. Two variables, density of large (>74 cm dbh) trees and understory cover of Vaccinium, explained much of the variation in microhabitat use. We conclude that the habitat of G. sabrinus in southeastern Alaska does not reflect emergent properties of old‐growth forest in southeastern Alaska and hypothesize that this pattern may be related to regional ecological differences that facilitate a more general lifestyle than populations in the Pacific Northwest. Furthermore, the effectiveness of Glaucomys sabrinus as an MIS in north temperate rain forest is suspect, illustrating that regional differences in ecology of a species warrant caution when considering the suitability of MIS among geographic areas.

Effects of multiple predator species on green treefrog (Hyla cinerea) tadpoles

Prey species that occur across a range of habitats may be exposed to variable communities of multiple predator species across habitats. Predicting the combined effects of multiple predators can be complex. Many experiments evaluating the effects of multiple predators on prey confound either variation in predator density with predator identity or variation in relative predator frequency with overall predation rates. We develop a new experimental design of factorial predator combinations that maintains a constant expected predation rate, under the null hypothesis of additive predator effects. We implement this design to evaluate the combined effects of three predator species (bass, aeshnid and libellulid odonate naiads) on mortality rate of a prey species, Hyla cinerea (Schneider, 1799) tadpoles, that occurs across a range of aquatic habitats. Two predator treatments (libellulid and aeshnid + libellulid) resulted in lower tadpole mortality than any of the other predator treatments. Variation in tadpole mortality across treatments was not related to coarse variation in microhabitat use, but was likely due to intraguild predation, which occurred in all predator treatments. Hyla cinerea tadpoles have constant, low survival values when exposed to many different combinations of predator species, and predation rate probably increases linearly with predator density.

Seasonal variation in diel activity and microhabitat use of an endemic New Zealand stream‐dwelling galaxiid fish

Summary1. Seasonal variation in microhabitat use and activity of 14 giant kokopu Galaxias argenteus, a drift‐feeding galaxiid fish, was compared using radiotelemetry.2. During winter giant kokopu predominantly used low velocities and intermediate depths by night and day. Activity recorded during 24 and 72 h periods indicated that fish were consistently active at night and inactive during the day. Activity data corresponded with point‐in‐time habitat use data, both of which indicated that fish were concealed amongst cover during the day and used open water habitats at night.3. During summer, giant kokopu used higher water velocities, shallower depths and coarser substrata, particularly at night but also occasionally during the day relative to winter. Giant kokopu were active by both day and night in summer, although periods of activity were less defined and less predictable than during winter.4. Adults used predictable home reaches at base‐flow, with most individuals repeatedly using of one or two cover locations within their ‘home’ reach. Reaches used by fish were relatively short (rarely exceeding 26 m) irrespective of season and always included a single pool‐riffle sequence.5. Diel and seasonal behaviour of giant kokopu was generally comparable with that exhibited by other drift feeding fish species in small temperate streams. However, the nocturnal activity of giant kokopu contrasts with activity patterns in various salmonids, indicating that the impact of predation by different drift feeding fish may vary considerably.

Relationships between locomotor performance, microhabitat use and antipredator behaviour in lacertid lizards

SummaryMicrohabitat use and antipredator behaviour (i.e. behavioural response to a bird model and refuge microhabitat) was measured in an experimental set‐up for 11 lacertid lizard species. Additionally, locomotor performance (sprint speed, climbing and clambering speed, manoeuvrability and endurance) of the same species was quantified.The results showed considerable interspecific variation in microhabitat use, behavioural response and choice of refuge microhabitat. Part of that variation could be linked to differences in locomotor capacity.Species that frequently made use of open microhabitats tended to be fast sprinters, but had limited endurance. The behavioural data suggest these species will not start running before the predator is close at hand, and thus having high sprint capacities might be more beneficial than great endurance.Species that spent most of their time on vertical elements appeared to be fast climbers. As such microhabitats tend to be quite exposed, lizards living there are conspicuous to predators and being able to escape fast seems relevant.Contrary to our expectations, species mostly observed in the vegetated microhabitats did not excel in clambering capacity or manoeuvrability. Possibly, dense vegetation constitutes a safe harbour and species may no longer be under selection for locomotor speed.Behavioural response when confronted with an aerial predator was context‐dependent in most species: most lizards fled more when in open or vertical microhabitats than when in densely vegetated ones. Moreover, when fleeing most species sought refuge in the vegetation. These findings support our idea that vegetated patches may constitute a safe harbour for lacertids.

The Relationship Among Swimming Performance, Courtship Behavior, and Carotenoid Pigmentation of Guppies in Four Rivers of Trinidad

In the laboratory, courtship behavior and carotenoid pigmentation of male guppies are condition-dependent traits, since their expression is affected by physical vigor and environmental factors such as water velocity and diet. Whether these relationships exist in guppies under field conditions is yet to be determined. We compared the swimming performance, courtship behavior, and carotenoid pigmentation of guppies from headwater and downstream localities in four rivers of Trinidad. Swimming performance and courtship behavior of males differed among rivers and between headwater and downstream sites. Guppies from headwater sites swam significantly faster and had higher display rates than those from downstream sites. Mean swimming performance across sites was positively correlated with mean water velocity, but was correlated with the number of orange color spots (carotenoid pigment) in only one river. These results indicate that the courtship behavior of Trinidadian guppies is condition-dependent because the amount of display behavior is positively correlated to swimming performance, a measure of physical endurance. The proximal cause for this condition-dependence may be predator induced variation in microhabitat use by guppies in headwater and downstream locations.