Seasonal variation of behavior and brain size in a freshwater fish

1. Teleost fishes occupy a range of ecosystem, and habitat types subject to large seasonal fluctuations. Temperate fishes, in particular, survive large seasonal shifts in temperature, light availability, and access to certain habitats. Mobile species such as lake trout (Salvelinus namaycush) can behaviorally respond to seasonal variation by shifting their habitat deeper and further offshore in response to warmer surface water temperatures during the summer. During cooler seasons, the use of more structurally complex nearshore zones by lake trout could increase cognitive demands and potentially result in a larger relative brain size during those periods. Yet, there is limited understanding of how such behavioral responses to a seasonally shifting environment might shape, or be shaped by, the nervous system.
2. Here, we quantified variation in relative brain size and the size of five externally visible brain regions in lake trout, across six consecutive seasons in two different lakes. Acoustic telemetry data from one of our study lakes were collected during the study period from a different subset of individuals and used to infer relationships between brain size and seasonal behaviors (habitat use and movement rate).
3. Our results indicated that lake trout relative brain size was larger in the fall and winter compared with the spring and summer in both lakes. Larger brains coincided with increased use of nearshore habitats and increased horizontal movement rates in the fall and winter based on acoustic telemetry. The telencephalon followed the same pattern as whole brain size, while the other brain regions (cerebellum, optic tectum, olfactory bulbs, and hypothalamus) were only smaller in the spring.
4. These findings provide evidence that flexibility in brain size could underpin shifts in behavior, which could potentially subserve functions associated with differential habitat use during cold and warm seasons and allow fish to succeed in seasonally variable environments.

     

Cost of predation avoidance in young-of-year lake trout (Salvelinus namaycush): growth differential in sub-optimal habitats

Selection of habitat to avoid predation may affect the diet of young-of-year (YOY) lake trout (Salvelinus namaycush). YOY lake trout may use inshore habitat to avoid predation; this habitat may be sub-optimal for growth. To test this, YOY lake trout were penned in nearshore and offshore pelagic areas of two arctic lakes. Toolik Lake had a lake trout population, the other lake, S6, did not. YOY lake trout in Toolik Lake lost weight, but those offshore lost less weight. The YOY lake trout in Lake S6 gained weight and those offshore gained more weight. The primary diet item of the YOY lake trout in both lakes during this experiment was the zooplankter Diaptomis probilofensis; it was also one of the most abundant species. However, its density inshore in Lake S6 was similar to inshore and offshore densities in Toolik Lake. The increased availability of alternative zooplankton prey in Lake S6 may account for the growth differential of YOY lake trout in Lake S6 relative to Toolik Lake. Bioenergetic modeling of YOY lake trout suggests that growth similar to that in the offshore of Lake S6 would be necessary for successful recruitment. If the reduced zooplankton availability in Toolik Lake leads to the reduced growth of YOY in the inshore and offshore pelagic areas, then these fish will be more susceptable to winter predation/starvation. For YOY lake trout to survive in Toolik Lake they most likely shift to feeding on benthic prey before the end of their first summer. Dept. of Chemical Engineering     

Seasonal habitat selection by lake trout (<Emphasis Type="Italic">Salvelinus namaycush</Emphasis>) in a small Canadian shield lake: constraints imposed by winter conditions

The need for cold, well-oxygenated waters significantly reduces the habitat available for lake trout (Salvelinus namaycush) during stratification of small temperate lakes. We examined the spatial and pelagic distribution of lake trout over two consecutive summers and winters and tested whether winter increased habitat availability and access to littoral regions in a boreal shield lake in which pelagic prey fish are absent. In winter, lake trout had a narrowly defined pelagic distribution that was skewed to the upper 3 m of the water column and spatially situated in the central region of the lake. Individual core areas of use (50% Kernel utilization distributions) in winter were much reduced (75%) and spatially non-overlapping compared to summer areas, but activity levels were similar between seasons. Winter habitat selection is in contrast to observations from the stratified season, when lake trout were consistently located in much deeper waters (>6 m) and widely distributed throughout the lake. Winter distribution of lake trout appeared to be strongly influenced by ambient light levels; snow depth and day length accounted for up to 69% of the variation in daily median fish depth. More restricted habitat use during winter than summer was in contrast to our original prediction and illustrates that a different suite of factors influence lake trout distribution between these seasons.     

Integration of acoustic telemetry and GIS to identify potential spawning areas for lake trout (Salvelinus namaycush)

Locations of potential spawning areas for lake trout (Salvelinus namaycush) were predicted in Lake Opeongo, Ontario, Canada using information gained via acoustic telemetry and geographic information system (GIS) technologies. From 1998 to 2000, 18 adult lake trout (mean fork length 553 mm) implanted with acoustic transmitters (battery life 2 years) were manually tracked. For evening fall locations within the erosive zone of the lake (determined using an existing sedimentation model), habitat variables (slope, depth, and effective fetch) were summarised using GIS. Sites selected by lake trout during the spawning window were in areas of mean fetch equal to 1.5 km and mean slope of 10.6% (n = 50 fixes). We used GIS to identify areas that matched the mean habitat criteria and thus locate potential spawning areas. This model correctly identified 19 of 21 known spawning sites, as well as additional sites used by spawning females in an earlier telemetry study. Depths of traditional fall netting sites are shallow compared to areas in which telemetered lake trout were found during evenings of the spawning period (means 3.1 vs. 5.1 m, respectively). Through the use of information on spawning habitat selection gained through telemetry and knowledge of the physical characteristics of the lake, we provide an alternative means of identifying potential spawning habitat for lake trout.     

Climate Change Expands the Spatial Extent and Duration of Preferred Thermal Habitat for Lake Superior Fishes

Climate change is expected to alter species distributions and habitat suitability across the globe. Understanding these shifting distributions is critical for adaptive resource management. The role of temperature in fish habitat and energetics is well established and can be used to evaluate climate change effects on habitat distributions and food web interactions. Lake Superior water temperatures are rising rapidly in response to climate change and this is likely influencing species distributions and interactions. We use a three-dimensional hydrodynamic model that captures temperature changes in Lake Superior over the last 3 decades to investigate shifts in habitat size and duration of preferred temperatures for four different fishes. We evaluated habitat changes in two native lake trout (Salvelinus namaycush) ecotypes, siscowet and lean lake trout, Chinook salmon (Oncorhynchus tshawytscha), and walleye (Sander vitreus). Between 1979 and 2006, days with available preferred thermal habitat increased at a mean rate of 6, 7, and 5 days per decade for lean lake trout, Chinook salmon, and walleye, respectively. Siscowet lake trout lost 3 days per decade. Consequently, preferred habitat spatial extents increased at a rate of 579, 495 and 419 km² per year for the lean lake trout, Chinook salmon, and walleye while siscowet lost 161 km² per year during the modeled period. Habitat increases could lead to increased growth and production for three of the four fishes. Consequently, greater habitat overlap may intensify interguild competition and food web interactions. Loss of cold-water habitat for siscowet, having the coldest thermal preference, could forecast potential changes from continued warming. Additionally, continued warming may render more suitable conditions for some invasive species.     

Ecosystem response to earlier ice break‐up date: Climate‐driven changes to water temperature,lake‐habitat‐specific production,and trout habitat and resource use

Climate warming has yielded earlier ice break‐up dates in recent decades for lakes leading to water temperature increases, altered habitat, and both increases and decreases to ecosystem productivity. Within lakes, the effect of climate warming on secondary production in littoral and pelagic habitats remains unclear. The intersection of changing habitat productivity and warming water temperatures on salmonids is important for understanding how climate warming will impact mountain ecosystems. We develop and test a conceptual model that expresses how earlier ice break‐up dates influence within lake habitat production, water temperatures and the habitat utilized by, resources obtained and behavior of salmonids in a mountain lake. We measured zoobenthic and zooplankton production from the littoral and pelagic habitats, thermal conditions, and the habitat use, resource use, and fitness of Brook Trout (Salvelinus fontinalis). We show that earlier ice break‐up conditions created a "resource‐rich" littoral–benthic habitat with increases in zoobenthic production compared to the pelagic habitat which decreased in zooplankton production. Despite the increases in littoral–benthic food resources, trout did not utilize littoral habitat or zoobenthic resources due to longer durations of warm water temperatures in the littoral zone. In addition, 87% of their resources were supported by the pelagic habitat during periods with earlier ice break‐up when pelagic resources were least abundant. The decreased reliance on littoral–benthic resources during earlier ice break‐up caused reduced fitness (mean reduction of 12 g) to trout. Our data show that changes to ice break‐up drive multi‐directional results for resource production within lake habitats and increase the duration of warmer water temperatures in food‐rich littoral habitats. The increased duration of warmer littoral water temperatures reduces the use of energetically efficient habitats culminating in decreased trout fitness.     

Dynamic micro-geographic and temporal genetic diversity in vertebrates: the case of lake-spawning populations of brown trout (Salmo trutta)

Conservation of species should be based on knowledge of effective population sizes and understanding of how breeding tactics and selection of recruitment habitats lead to genetic structuring. In the stream‐spawning and genetically diverse brown trout, spawning and rearing areas may be restricted source habitats. Spatio–temporal genetic variability patterns were studied in brown trout occupying three lakes characterized by restricted stream habitat but high recruitment levels. This suggested non‐typical lake‐spawning, potentially representing additional spatio–temporal genetic variation in continuous habitats. Three years of sampling documented presence of young‐of‐the‐year cohorts in littoral lake areas with groundwater inflow, confirming lake‐spawning trout in all three lakes. Nine microsatellite markers assayed across 901 young‐of‐the‐year individuals indicated overall substantial genetic differentiation in space and time. Nested gene diversity analyses revealed highly significant (≤P = 0.002) differentiation on all hierarchical levels, represented by regional lakes (F_LT = 0.281), stream vs. lake habitat within regional lakes (F_HL = 0.045), sample site within habitats (F_SH = 0.010), and cohorts within sample sites (F_CS = 0.016). Genetic structuring was, however, different among lakes. It was more pronounced in a natural lake, which exhibited temporally stable structuring both between two lake‐spawning populations and between lake‐ and stream spawners. Hence, it is demonstrated that lake‐spawning brown trout form genetically distinct populations and may significantly contribute to genetic diversity. In another lake, differentiation was substantial between stream‐ and lake‐spawning populations but not within habitat. In the third lake, there was less apparent spatial or temporal genetic structuring. Calculation of effective population sizes suggested small spawning populations in general, both within streams and lakes, and indicates that the presence of lake‐spawning populations tended to reduce genetic drift in the total (meta‐) population of the lake.     

Landscape topography and the distribution of Lahontan cutthroat trout (Oncorhynchus clarki henshawi) in a high desert stream

Lahontan cutthroat trout, Oncorhynchus clarki henshawi, are currently limited in their distribution to a patchwork of small isolated populations, the result of habitat degradation and natural variation in landscape and in-stream conditions. The objectives of this study were to determine if landscape topography influences trout distribution, and if water temperatures control this response. The work was carried out in a sub-basin of the Quinn River system, McDermitt Creek, which drains the sagebrush desert of southeastern Oregon and northern Nevada. Headwater tributaries of this creek consist of alternating canyon-confined and valley bounded reaches. Trout within these systems are challenged by low discharge and high temperatures during the summer, and anchor ice during the winter. Contiguous whole stream surveys were used to look at trout distribution during the summer of 2003 and spring and fall of 2004. Our results suggested that topography can affect trout distribution. Trout numbers were highest in areas with greater numbers of nick-points (the transition zones between less confined and more confined valley segments) and greater valley confinement. Additionally, in the downstream portion of our headwater reaches, more trout were found in nick-points than expected based on the availability of this habitat type. Our data suggest that hyporheic inputs may be high in such areas, thus providing trout with shelter from warm water in the summer, anchor ice in the winter, and shallow stream depths during all seasons. Spatial occurrence of these areas of refugia can be taken into consideration when planning land use activities and restoration efforts. Further research is required to confirm that topography can affect the distribution of Lahontan cutthroat trout in other systems, and to better understand the mechanisms behind these patterns.     

Seasonal and spatial microhabitat selection and segregation in young Atlantic salmon, Salmo salar L., and brown trout, Salmo trutta L., in a Norwegian river

Seasonal microhabitat selection by sympatric young Atlantic salmon and brown trout was studied by diving. Both species, especially Atlantic salmon, showed seasonal variation with respect to surface and mean water velocities and depth. This variation is partly attributed to varying water flows and water temperatures. In winter the fish sought shelter in the substratum. A spatial variation in habitat use along the river due to different habitat availabilities was observed. Both species occupied habitats within the ranges of the microhabitat variables, rather than selecting narrow optima. It is hypothesized that the genetic basis allows a certain range to the behavioural response. Microhabitat segregation between the two species was pronounced, with brown trout inhabiting the more slow-flowing and partly more shallow stream areas. Atlantic salmon tolerated a wider range of water velocities and depths. Habitat suitability curves were produced from both species. It is suggested that habitat suitability curves that are based on observations of fish occupancy of habitat at median or base flow may not be suitable in habitat simulation models, where available habitat is projected at substantially greater water flows.     

Long‐term impacts of invasive species on a native top predator in a large lake system

1. Declining abundances of forage fish and the introduction and establishment of non‐indigenous species have the potential to substantially alter resource and habitat exploitation by top predators in large lakes. 2. We measured stable isotopes of carbon (δ¹³C) and nitrogen (δ¹⁵N) in field‐collected and archived samples of Lake Ontario lake trout (Salvelinus namaycush) and five species of prey fish and compared current trophic relationships of this top predator with historical samples. 3. Relationships between δ¹⁵N and lake trout age were temporally consistent throughout Lake Ontario and confirmed the role of lake trout as a top predator in this food web. However, δ¹³C values for age classes of lake trout collected in 2008 ranged from 1.0 to 3.9‰ higher than those reported for the population sampled in 1992. 4. Isotope mixing models predicted that these changes in resource assimilation were owing to the replacement of rainbow smelt (Osmerus mordax) by round goby (Neogobius melanostomus) in lake trout diet and increased reliance on carbon resources derived from nearshore production. This contrasts with the historical situation in Lake Ontario where δ¹³C values of the lake trout population were dominated by a reliance on offshore carbon production. 5. These results indicate a reduced capacity of the Lake Ontario offshore food web to support the energetic requirements of lake trout and that this top predator has become increasingly reliant on prey resources that are derived from nearshore carbon pathways.     

Use of cover habitat by bull trout, <Emphasis Type="Italic">Salvelinus confluentus</Emphasis>, and lake trout, <Emphasis Type="Italic">Salvelinus namaycush</Emphasis>, in a laboratory environment

Lacustrine-adfluvial bull trout, Salvelinus confluentus, migrate from spawning and rearing streams to lacustrine environments as early as age 0. Within lacustrine environments, cover habitat provides refuge from potential predators and is a resource that is competed for if limiting. Competitive interactions between bull trout and other species could result in bull trout being displaced from cover habitat, and bull trout may lack evolutionary adaptations to compete with introduced species, such as lake trout, Salvelinus namaycush. A laboratory experiment was performed to examine habitat use and interactions for cover by juvenile (i.e., <80 mm total length) bull trout and lake trout. Differences were observed between bull trout and lake trout in the proportion of time using cover (F _1,22.6 = 20.08, P < 0.001) and bottom (F _1,23.7 = 37.01, P < 0.001) habitat, with bull trout using cover and bottom habitats more than lake trout. Habitat selection ratios indicated that bull trout avoided water column habitat in the presence of lake trout and that lake trout avoided bottom habitat. Intraspecific and interspecific agonistic interactions were infrequent, but approximately 10 times greater for intraspecific interactions between lake trout. Results from this study provide little evidence that juvenile bull trout and lake trout compete for cover, and that species-specific differences in habitat use and selection likely result in habitat partitioning between these species.     

Lake morphometry predicts the degree of habitat coupling by a mobile predator

Habitat coupling is an ecosystem process whereby semi-discontinuous habitats are connected through the movement of energy and nutrients by chemical, physical or biological processes. One oft-cited example is that of littoral–pelagic coupling in lakes. Theory has argued that such habitat coupling may be critical to food web dynamics, yet there have been few empirical studies that have quantified ecological factors that affect the degree of habitat coupling in ecosystems. Specifically, the degree to which habitat coupling occurs across important physical gradients has largely been ignored. To address this, we investigate the degree of littoral habitat coupling (i.e. the degree to which a top predator lake trout, Salvelinus namaycush, derives energy from the littoral zone) along a gradient of lake shape, where lake shape modifies the relative quantity of coupled epilimnetic benthic and pelagic habitats within each lake. Herein we demonstrate that littoral habitat coupling is intensified in simple circular lakes compared to their reticulate counterparts in seven Canadian Shield lakes. Although the more reticulate lakes had larger areas of epilimnetic benthic habitat, littoral food sources comprised 11% compared to 24% of lake trout diet in reticulate and circular lakes, respectively. This heightened interaction in circular lakes also appears to translate into increased omnivory in more circular lakes compared to reticulate lakes such that lake trout of circular lakes have a significantly lower trophic position than lake trout of reticulate lakes (F_1,5=6.71 p=0.05). These results suggest that it is the accessibility of littoral production via thermal refugia, and not the amount of littoral production, that determines the degree to which lake trout couple littoral and pelagic habitats in lakes.     

Deciphering lifelong thermal niche using otolith δ18O thermometry within supplemented lake trout (Salvelinus namaycush) populations

1. The selection of thermal habitat by fish is strongly regulated by physiology and behaviour. However, delineation of a species lifelong thermal niche remains technically challenging. Lake trout (Salvelinus namaycush) survival and productivity are recognised as being tightly linked to a somewhat restricted thermal habitat. The factors guiding temperature selection during each life stage remain poorly understood.
2. In this study, we tested the significant factors controlling the realised thermal niche of lake trout from two southern Quebec small boreal lakes that experienced supplementation stocking during the last 20 years. We used oxygen stable isotope (δ¹⁸O) thermometry of otolith calcium carbonates (aragonite) using secondary-ion mass spectrometry to estimate experienced lifelong temperatures. We investigated the thermal habitat of lake trout with known genotypes (local, hybrid, and stocked).
3. Ontogeny and genetic origin influenced temperature selection in both studied lake trout populations. Young-of-the-year consistently used warmer, shallower habitats (10.7 ± 2.6°C, 7.5 m depth) prior to a juvenile transition to colder and deeper waters (8.5 ± 3.3°C, 10 m depth). Stocked lake trout, originating from a genetically distinct ecotype, exhibited a more variable thermal niche, with some individuals consistently using warmer habitat (10.4 ± 1°C) than local fish. Their hybrid progeny also occupied a warmer thermal niche, intermediate to the parental strains. We propose that increased fat content and genetic origin are potential explanatory factors for warmer temperature use.
4. This study reiterates that high-resolution otolith δ¹⁸O thermometry is a uniquely well-suited approach for unravelling the multiple factors that influence lifelong temperature selection in fish. Our results illustrate that the realised thermal niche is influenced by a genetic–environment interaction.

     

Shifts in abundance and growth of slimy sculpin in response to changes in the predator population in an arctic Alaskan lake

Lake trout (Salvelinus namaycush) in Toolik Lake are tightly coupled to the benthos, since they have no pelagic forage fishes. Slimy sculpins (Cottus cognatus) are a prey of lake trout and the soft sediment chironomids are an important prey for the sculpin. Our previous work showed that the median size of lake trout in Toolik Lake had decreased significantly between 1977 and 1986, and smaller lake trout are likely to be less effective as sculpin predators. Using our historic data on the slimy sculpin population from 1978, we took advantage of the recent change in the predator community to examine for subsequent changes in the sculpin community. Between 1978 and 1987, the percentage of slimy sculpin caught in the soft sediments has increased (25% to 39.5%). In 1987 there was a significant difference in the mean weight of sculpin caught on different substrates. The mean individual weight of sculpins increased from the nearshore rock area to the rock/soft-sediment interface to the soft sediments. There was no difference in mean individual weight with habitat in 1978. The mean total length at age for slimy sculpins during this time has also increased significantly. We suggest that the risk of predation while foraging in the soft sediments has declined. The increased use of the soft sediment area appears to have contributed to their increased growth, likely due to greater food abundance.     

Effect of fluctuating flow and temperature on cover type selection and behaviour by juvenile brown trout in artificial flumes

Brown trout Salmo trutta in a flume used cover more often and were more aggregated at low water temperatures in winter compared with summer. Cover combinations providing the most cover (overhead, visual and velocity cover) were preferred in winter whereas velocity refuges were preferred in late summer; and brown trout rarely used any of these cover structures in early summer. Flow affected cover use especially in winter, when most of the trout moved to shelters during the first high flow period. Movements by brown trout were most frequent in early summer. The much higher aggression rate in summer compared with winter decreased during the first period of high flow in both summer experiments. The results indicate seasonal changes in cover habitat and cover type preferences suggesting that habitat complexity is important, and availability of cover is particularly important during different seasons and fluctuating flow.     

Among‐individual diet variation within a lake trout ecotype: Lack of stability of niche use

In a polyphenic species, differences in resource use are expected among ecotypes, and homogeneity in resource use is expected within an ecotype. Yet, using a broad resource spectrum has been identified as a strategy for fishes living in unproductive northern environments, where food is patchily distributed and ephemeral. We investigated whether specialization of trophic resources by individuals occurred within the generalist piscivore ecotype of lake trout from Great Bear Lake, Canada, reflective of a form of diversity. Four distinct dietary patterns of resource use within this lake trout ecotype were detected from fatty acid composition, with some variation linked to spatial patterns within Great Bear Lake. Feeding habits of different groups within the ecotype were not associated with detectable morphological or genetic differentiation, suggesting that behavioral plasticity caused the trophic differences. A low level of genetic differentiation was detected between exceptionally large‐sized individuals and other piscivore individuals. We demonstrated that individual trophic specialization can occur within an ecotype inhabiting a geologically young system (8,000–10,000 yr BP), a lake that sustains high levels of phenotypic diversity of lake trout overall. The characterization of niche use among individuals, as done in this study, is necessary to understand the role that individual variation can play at the beginning of differentiation processes.     

Effects of Fish-farm Activity on the Limnetic Community Structure of Brown Trout, Salmo trutta, and Arctic Charr, Salvelinus alpinus

Establishment of four fish-farms during the period 1971 to 1994 in the oligotrophic lake Skogseidvatnet affected Arctic charr, Salvelinus alpinus, but not brown trout, Salmo trutta. From 1971 to 1987, an increase in mean individual size of Arctic charr was recorded, while the mean individual size of brown trout remained stable. Arctic charr were found to use deeper benthic areas than brown trout. Approximately 8% of the Arctic charr population (>26cm), were found to switch to waste food from fish-farms, resulting in a novel feeding habitat for the species. They were, however, found in gillnets distant from the fish farm cages, indicating high mobility. The habitat segregation between the two species can most likely be explained by selective differences and asymmetric competition with brown trout as the dominant species. Based on the present results, changes in the Arctic charr population may be due to increased food availability and due to a new habitat use as a waste food feeder. The reason for the brown trout population to have remained stable with respect to mean size, growth pattern and habitat use, may be due to a different diet choice than Arctic charr in this lake. Brown trout were found to feed mainly on terrestrial insects, while Arctic charr fed mainly on zooplankton and on waste food.     

Individual variation in habitat use and growth of male and female brown trout

We examined variation in growth and habitat use of individually PIT‐tagged brown trout Salmo trutta in three stream enclosures, each divided into a fine substrate, deep pool habitat and a coarse substrate, shallow habitat. Habitat use and movements of individual fish were monitored continually by placing PIT detectors between habitats. All fish were measured and weighed biweekly over a three month period. There was no significant relationship between habitat use and initial body size, nor was there a consistent relationship between habitat use and densities of benthic macroinvertebrates or abundance of drifting invertebrates in the two habitats. Most habitat changes occurred at night, with activity peaks just prior to sunrise and after sunset. Trout used pools more at night than during the day. Within any given day, diurnal and nocturnal habitat use of individual fish varied little, with variation greater at night than during the day. Partial habitat segregation by sex was observed; only males used pools extensively during daytime, whereas males and females used riffles.
Growth rate was positively related to use of pools during daytime but not at night. Growth rate was also affected by enclosure, with growth rates being highest in the most downstream enclosure, which had the deepest pool (mean of 42 cm) and lowest in the most upstream enclosure, which had the shallowest pool (mean of 28 cm). A complete exchange of trout between the most upstream and downstream enclosure indicated that the enclosure effect was due to physical differences and not to individual fish differences between enclosures. The effect appears to have been caused by differences in depth as daytime use of pools was correlated with the area of the pool ≥35 cm deep, and production of trout biomass per enclosure was directly related to mean pool depth. Our results suggest that there is a relationship between habitat use and growth of individuals that is independent of body size, but that this relationship is influenced by sex of the fish and by the physical characteristics of the environment. Further, the data indicate that short‐term behavioral decisions on habitat use by brown trout have a potential effect on longer‐term individual fitness through growth rates.     

Spatial selection in captive adult female chimpanzees

Spatial selection refers to an animal's frequent use of certain areas of its enclosure or range. Through differential use of habitat, an individual can limit the amount of time spent in close proximity to other group members. The four adult female chimpanzees at the Tulsa Zoo were studied to determine if they used their enclosure differently from one another, if each had selected areas it occupied most frequently, and if an individual's preferred area was used by other female group members. Pairwise comparisons showed that the females used their island habitat differently from one another with the exception of one pair. Although these two females overlapped in their use of the enclosure, they separated their use temporally, thereby reducing the amount of time spent in close proximity to one another. Each female had a selected site that she occupied more frequently than did the other females. However, there was variation in the extent to which the females occupied each other's selected sites. Time of day and temperature had no effect on use of the habitat, however, one female showed a seasonal variation in her use of the enclosure. The spatial selection exhibited by these females may be comparable to the use of core areas by wild female chimpanzees. © 1994 Wiley-Liss, Inc.