Microhabitat Selection Patterns Research Articles

Coping with drought? The hidden microhabitat selection and underground movements of amphisbaenians under summer drought conditions

Abstract Habitat selection is a dynamic process that depends on many environmental variables that can vary with weather conditions. This is important because, within a context of global change, extreme weather events, such as severe droughts, are predicted to become more frequent. We examined the patterns of microhabitat selection and underground movements (using PIT-tag telemetry) of a strictly fossorial reptile, the North African checkboard amphisbaenian Trogonophis wiegmanni, during the summer drought period. We aimed to test whether changes in strategies of habitat use and movements could allow this amphisbaenian to cope with unfavorable weather. We found that during the summer drought period, T. wiegmanni did not use the microhabitats in relationship to their availability, but particularly selected sites with high abundance of rocks but also areas under a high cover of bushes, where environmental conditions were more favorable. We also found, using PIT-tag telemetry, that the numbers of T. wiegmanni individuals located under rocks and their activity (number of days with movements) decreased largely in summer. However, the animals were not entirely inactive, but, especially males were active below the ground under bushes and made some relatively long underground hidden movements between favorable areas.

Seasonal patterns of microhabitat selection in the Southern Iberian spined-loach Cobitis paludica

The Southern Iberian spined-loach Cobitis paludica is an Iberian endemism threatened by human activities, including habitat destruction. For this reason, the development of conservation and the recovery plans for the species calls for a precise knowledge of its habitat requirements. Here, microhabitat use and selection patterns were investigated to determine the limiting factors for the species in different seasons, corresponding to a gradient in flow conditions. The microhabitat of the loach was analysed in the River Jarama (Tagus River basin, central Spain) in the period of maximum activity between March and September 2013. No significant differences in microhabitat use were found between males and females, and only very weak ontogenetic changes were detected. The microhabitat used by the loach varied significantly throughout the study period, generally adapting to the flow-mediated dynamics of available habitat. The most stable pattern throughout the year was the use of very low water velocities. Additionally, the loach made selective use of certain microhabitat features, with slight adjustments to the seasonally changing habitat conditions. The loach significantly selected positions with abundant silt substrate and aquatic vegetation, and avoided coarser substrates. The availability of fine substrates and abundant vegetation is therefore a critical habitat requirement for the loach, which needs instream structures that provide foraging substrate, refuge and safe positions for spawning. Selection of refuge elements (deep habitats, aquatic vegetation) was especially apparent under low-flow conditions. Human activities leading to the loss of these critical microhabitats may threaten the survival of already scarce loach populations.

Land-use change alters associations between personality and microhabitat selection.

Ecologists commonly assess ecological patterns at the population level, focusing on the average response of all individuals within a population, but to predict how populations will respond to land-use change we must understand how changes to habitat differentially affect individuals within a population. For example, forest management is a widespread type of land-use that impacts wildlife through the loss of key habitat features, but individuals within a population may vary in their responses to this loss due to differences in habitat selection among individuals. Specifically, intraspecific variation in habitat selection has been linked to animal personalities (i.e., consistent behavioral differences among conspecifics), but previous research has not examined whether the relationship between personality and habitat selection is influenced by land-use change. To address this knowledge gap, we tested the hypothesis that land-use change alters the association between personality and microhabitat selection in small mammals. Specifically, we investigated two main questions: (1) To what extent are personality type and microhabitat selection correlated among conspecifics? (2) Does land-use change alter individual patterns of microhabitat selection? To answer these questions, we conducted a large-scale field experiment over 4 years, contrasting unmanaged forest (control) with managed forest (two silvicultural treatments) in Maine, USA. We examined the relationships between habitat selection and personality traits in deer mice (Peromyscus maniculatus) and southern red-backed voles (Myodes gapperi). We found that personality traits were correlated with microhabitat selection at multiple spatial scales. Furthermore, land-use change altered these patterns of selection; resulting in either the loss of personality-associated selection or in novel patterns of selection in managed forests. These findings suggest that promoting structural complexity at multiple spatial scales, such as by interspersing stands of mature forest with managed stands, may maintain a variety of intraspecific habitat selection patterns and the associated ecological outcomes.

Determinants of large‐scale spatial distribution and seasonal microhabitat selection patterns of the endangered freshwater blenny Salaria fluviatilis in the Ebro River basin, Spain

Abstract The freshwater blenny Salaria fluviatilis is an endangered fish species with populations that are in rapid decline, largely owing to habitat degradation caused by human activity. This situation highlights the urgent need to develop measures for the conservation and recovery of the species based on a deep understanding of its specific habitat requirements. In this study, spatial distribution and habitat selection patterns were investigated to determine the limiting factors for the species at different times of the year and at different spatial scales, from macro to microhabitats. The presence of the freshwater blenny was assessed at 127 sites in the Ebro River basin, Spain, between 2002 and 2012. It was only detected at 25 sites, corresponding to the intermediate and lower reaches of medium‐sized tributaries and in the main river, in accordance with the ecology of the species. Whether the species was present depended on the physicochemical, habitat and biological conditions of the study sites. Freshwater blenny was very sensitive to organic pollution and eutrophication, the deterioration of substrate composition and channel structure, and the degradation of aquatic and riparian vegetation. Freshwater blenny showed a selective use of microhabitat locations with high current velocity, linked to gravel or cobble substrate. It was also observed that the species is capable of adapting its selection behaviour to the flow‐mediated seasonal changes in its physical environment. Although the results presented indicate that the species is not a microhabitat specialist, individual survival is likely to be dependent on the availability of key microhabitats, which must be protected against detrimental human activity.

Chemical cues may allow a fossorial amphisbaenian reptile to avoid extremely saline soils when selecting microhabitats

When selecting optimal habitats, animals should rely on detecting environmental cues that indicate the suitability of a given site. In fossorial animals, restrictions of the underground environment might limit the opportunities for habitat selection. However, field observations of some fossorial amphisbaenian reptiles indicate that microhabitat occupancy is not random. This might simply result from the low survival of individuals in suboptimal habitats, but it may reflect active behavioral selection. We suggest that, in the fossorial environment, chemical cues may be very important for actively selecting or avoiding specific microhabitats. Here, we tested the ability of Trogonophis wiegmanni amphisbaenians to discriminate and select different types of substrates by using chemical cues alone. In laboratory preference tests, amphisbaenians selected soils with low salinity levels (natural or experimentally manipulated), mimicking the microhabitat selection patterns observed in the wild. Moreover, chemosensory tests measuring tongue-flick rates showed that amphisbaenians discriminated using chemical cues alone between soil types according to natural salinity levels, and also between manipulated chemical stimuli with different salinity levels. These results suggest that the microgeographic patterns of distribution of these amphisbaenians are due to their ability to use substrate chemical cues to actively avoid extremely saline soils. and select optimal microhabitats.

Ghost‐busting: patch occupancy and habitat preferences of Ocyale ghost (Araneae: Lycosidae), a single site endemic in north‐western Madagascar

AbstractMicroendemic species are of great conservation concern due to their vulnerability to stochastic events and environmental change. Therefore, understanding the basic ecology of such organisms is integral to future efforts to conserve them. Here, we present the first ecological study of the only known population of Ocyale ghost Jocque & Jocqué 2017 – the single species within this genus in Madagascar – located at a small lake shore in the north‐west of the island. We aimed to reveal spatial patterns of microhabitat selection and patch occupancy in relation to environmental covariates, including distance to lake edge, topography and sand coverage. We found microhabitat selection to be strong in our occupancy models, with plots closer to the lake edge and with a higher proportion of sand showing the highest estimated occupancy. We suggest decreases in prey availability and changes in the physical characteristics of the substrate in relation to the distance from lake shore and sand availability (important for burrowing and temperature regulation), respectively, as potential factors behind occupancy. We discuss our findings in the context of the proportional underrepresentation of invertebrates in conservation research, which threatens the persistence of endemic and microendemic invertebrates in the face of significant global and local environmental change.

Realized niche and microhabitat selection of the eastern green lizard (Lacerta viridis) at the core and periphery of its distribution range.

The available range of habitats and suitable abiotic conditions like temperature and radiation tends to be narrower toward the periphery of the distribution range of species. Peripheral populations of generalist species could then be more specialized and have a smaller and differentiated realized niche (habitat niche in our study) compared to populations at the core. Likewise, patterns of microhabitat selection can differ between periphery and core. In our study, we compared niche size and microhabitat selection among core (Bulgaria) and northern peripheral (Germany, Czech Republic) populations of Lacerta viridis and estimated niche differentiation among regions. We collected data on vegetation structure and abiotic parameters at the microhabitat scale in each region. In order to compare niche size among regions and estimate niche differentiation, we built multidimensional niche hypervolumes. We applied generalized linear mixed models and model averaging, accounting for spatial autocorrelation when necessary, to analyze microhabitat differences among regions and microhabitat selection in each region. Peripheral populations were more specialized, having a smaller niche than core ones, and their niche differed from that in the core (Sørensen overlap in all comparisons <0.3). Microhabitats at the periphery had lower radiation and soil compaction and less structured vegetation. Microhabitat selection at the core depended solely on abiotic parameters, while at the periphery it was defined by only vegetation structure (Czech Republic) or a combination of both, vegetation structure, and abiotic factors (Germany). Thus, peripheral populations seem to compensate for overall harsher climatic conditions by responding to different parameters of the microhabitat compared to core populations. We suggest specific conservation measures for L. virids in each studied region and point out the general implications of a higher specialization degree of peripheral populations in relation to climate change and habitat fragmentation.

Microtopography determines the habitat quality of a threatened peatland butterfly at its southern range margin

Knowledge of the ecology of pre-adult stages of an organism at its species’ range margins is a prerequisite for conserving species, especially for understanding its responses to future climate changes. Largely sedentary premature life stages require specific living conditions within a relatively small area. Such conditions are created by vegetation structure heterogeneity and a microclimate gradient, generated by varying microtopography. We investigated the microhabitat selection patterns of egg-laying females and overwintering caterpillars of peatland butterfly Coenonympha tullia relative to vegetation composition, water quantity and microclimatic conditions across microtopographic zones of transition mire at the species’ southern range margin. We showed that (1) small-scale variability in mire microtopography determines oviposition site selection and larval presence; (2) microhabitats of pre-adult stages were largely confined to the intermediate microtopographic zone of the transition mire (flats); (3) egg-laying females and overwintered larvae preferred microsites with high coverage of main hostplants (Trichophorum alpinum, Carex lasiocarpa, C. limosa, C. panicea), and those with more humid and cooler summertime conditions than on hummocks; (4) females and larvae avoided shallow hollows permanently filled with water. The vegetation structure of flats enables the females to select spots with sufficient humidity for egg development, and allows the larvae to change their location according to suitable thermal and moisture conditions. We also discuss poor prospects for species in view of impacts of future climate changes on mire ecosystems.

Spatial ecology and habitat selection of eastern hognose snakes

ABSTRACTThe eastern hognose snake (Heterodon platirhinos) is a species of conservation concern, especially in the northeastern portion of its range. They remain relatively common at Cape Cod National Seashore, Barnstable County, Massachusetts, USA, where we studied their spatial ecology and habitat selection. We radio‐tracked 17 adult snakes (10 F, 7 M) from May 2009 to November 2011, yielding 765 relocations. We conducted a use‐availability analysis to investigate patterns of microhabitat selection using a subset of snake locations. We conducted a compositional analysis of habitat selection at multiple spatial scales within home ranges using a high‐resolution (1‐m pixel size) vegetation cover map of the study area. Snakes moved frequently and had large home ranges ( = 35.4 ha) relative to other snake species of similar body size but exhibited variation in home range size among individuals (1–209 ha). Movements peaked at different times of year for each sex, and were most different between sexes in fall. In gravid females, movement was significantly greater in the 2‐week post‐oviposition period versus the 2‐week pre‐oviposition period. Estimates of home range and average daily movements ( = 30.1 m/day) were lower than estimates from other studies of eastern hognose snakes, possibly because of a greater density of resources at our study area. Probability of snake habitat use increased with grass and leaf litter and decreased with open soil. Compositional analysis revealed a strong avoidance of open dune areas. A comparison of edge density between use and random locations within home ranges revealed an apparent preference for edge habitat. We recommend that resource managers should limit recreational disturbance to and maintain the patchy mosaic of early successional vegetation with abundant edge to ensure the persistence of appropriate habitat for the species. We identified the timing of peak seasonal movements and recommend that this information be used to help prevent road mortality for this important population. © 2017 The Wildlife Society.

Differences in microhabitat selection patterns between a remnant and constructed landscape following management intervention

Context Achieving successful conservation outcomes in habitat creation and reintroductions requires an understanding of how species use their habitat and respond to these interventions. However, few initiatives directly compare microhabitat selection between remnant and managed habitats to measure effectiveness and evaluate outcomes. Probability of detection is also rarely included in studies on microhabitat use, which may lead to erroneous conclusions if detectability varies between variables. Methods In this study, we used the endangered green and golden bell frog (Litoria aurea) to compare differences in microhabitat-use patterns in both a remnant and a constructed habitat. A detectability study was also conducted to determine detection probabilities among microhabitats. Key results Aquatic vegetation was used more than expected in both the remnant and constructed habitats, and rock piles were utilised less than expected in the constructed habitat, despite their recommendation in most habitat templates. We found that detection probabilities altered the outcomes of abundance estimates for nearly all the measured microhabitat variables. Conclusions Future management for this species should focus on providing high proportions of aquatic vegetation. Furthermore, although rock piles have been utilised greatly in past L. aurea habitat creation, placing large rocks on a managed site is expensive and time consuming. Future management initiatives may need to focus on providing smaller proportion of rocks, which would be a more appropriate use of resources. Implications With conservation management projects increasing over the next few decades, understanding habitat use before implementing strategies should be a priority as it will provide important insights and inform decision-making for optimum habitat creation and restoration. Furthermore, accounting for detectability in microhabitat use studies is essential to avoid wrong conclusions that may negatively affect the success of ecological management strategies.

Development of Habitat Suitability Indices for the Candy Darter, with Cross‐Scale Validation across Representative Populations

AbstractUnderstanding relationships between habitat associations for individuals and habitat factors that limit populations is a primary challenge for managers of stream fishes. Although habitat use by individuals can provide insight into the adaptive significance of selected microhabitats, not all habitat parameters will be significant at the population level, particularly when distributional patterns partially result from habitat degradation. We used underwater observation to quantify microhabitat selection by an imperiled stream fish, the Candy Darter Etheostoma osburni, in two streams with robust populations. We developed multiple‐variable and multiple‐life‐stage habitat suitability indices (HSIs) from microhabitat selection patterns and used them to assess the suitability of available habitat in streams where Candy Darter populations were extirpated, localized, or robust. Next, we used a comparative framework to examine relationships among (1) habitat availability across streams, (2) projected habitat suitability of each stream, and (3) a rank for the likely long‐term viability (robustness) of the population inhabiting each stream. Habitat selection was characterized by ontogenetic shifts from the low‐velocity, slightly embedded areas used by age‐0 Candy Darters to the swift, shallow areas with little fine sediment and complex substrate, which were used by adults. Overall, HSIs were strongly correlated with population rank. However, we observed weak or inverse relationships between predicted individual habitat suitability and population robustness for multiple life stages and variables. The results demonstrated that microhabitat selection by individuals does not always reflect population robustness, particularly when based on a single life stage or season, which highlights the risk of generalizing habitat selection that is observed during nonstressful periods or for noncritical resources. These findings suggest that stream fish managers may need to be cautious when implementing conservation measures based solely on observations of habitat selection by individuals and that detailed study at the individual and population levels may be necessary to identify habitat that limits populations.Received March 30, 2016; accepted July 19, 2016Published online October 7, 2016

Resource partitioning and niche segregation in a steppe bird assemblage

Niche theory predicts that coexisting species will partition resources to limit the effects of interspecific competition. We examined microhabitat partitioning in six sets of steppe birds associated to agroecosystems in central Spain (female and male Great Bustards Otis tarda, female and male Little Bustards Tetrax tetrax, Red-legged Partridges Alectoris rufa and Eurasian Stone-curlews Burhinus oedicnemus) to estimate realized niche breadth, overlap and segregation. Principal Components Analysis on data from used and random microhabitat locations produced two axes we retained for analysis related with two key factors: cover-visibility and food availability. Non-parametric kernel density functions were calculated for each of the PCA axes and species (or sexes), and niche overlap estimated as the area shared between species’ density functions. Null models were run to evaluate overlap significance. In analyses of microhabitat selection by the six sets of birds, 13 out of 15 pairs had significant resource partitioning and niche segregation, except for the pairs partridge and female Great Bustard and the two sexes of Great Bustard. Eurasian Stone-curlew showed wider trophic niche breadth, although segregated from the other species, probably because of its higher invertebrate requirements. Great and Little Bustards segregated in both niche axes, selecting microhabitat according to their body size. Accessibility to food resources and shelter seems to be similar for partridges and female Great Bustards, overlapping in their selection, which may indicate the existence of segregation in other niche factors (e.g., feeding habits). Great Bustard males showed niche overlap with females. Little Bustard males showed feeding microhabitat selection patterns similar to those of females, although they preferred more open microhabitats to meet their sexual display requirements. The entire assemblage had significantly less overlap than expected by chance, suggesting that differential microhabitat selection and realized niche partitioning may explain coexistence in steppe bird communities. Our results suggest that the maintenance of different microhabitat structure should be a priority in the management of agricultural environments.

Microhabitat selection and diel patterns of zooplankton in a Mediterranean temporary pond

Changes in zooplankton microhabitat use in lakes through diel migrations (vertical and horizontal) have been related to habitat heterogeneity and to predation pressure, among other factors. However, there is a controversy concerning the effectiveness of diel migrations in temporary ponds, due to the shallowness of these systems and their distinct aquatic predator communities (mainly macroinvertebrates and amphibians). In order to test if diel microhabitat selection patterns described from lakes hold in temporary ponds, we developed a study using funnel traps at different zones of the pond (high and low vegetation density; surface and bottom of the pond) that were checked during the day and at night. Additionally, we assessed predation risk by sampling the macroinvertebrate community at the same time. In the studied Mediterranean temporary pond, zooplankton exhibited diel patterns of microhabitat selection: cladocerans showed a diel horizontal pattern, whereas copepods showed a diel vertical pattern. Results suggest that microhabitat selection and the associated diel pattern may be explained by both biological (potential predation) and environmental drivers (habitat heterogeneity and protection against ultraviolet radiation).

Crayfishes of the Apalachicola Ravines, Northern Florida: A Search for the Fireback Crayfish,Cambarus pyronotus

The series of steep, wooded ravines along the eastern side of the Apalachicola River in Gadsden and Liberty counties, FL, is recognized for its rich biodiversity. Little recent information is available on crayfishes of this unique ecosystem. During surveys conducted from 1939–1941, 5 taxa, including one undescribed species (now Cambarus pyronotus [Fireback Crayfish]), were recorded. No crayfish studies were conducted in the Apalachicola Ravines in the ensuing 60 years, and the conservation status of C. pyronotus remained unknown. From June 1999–February 2002, we surveyed the Apalachicola Ravines to determine distributional limits and stream-by-stream occurrence of C. pyronotus and evaluate its conservation status in relation to the regional system of protected lands. We recorded 8 species of crayfishes, including 4 primary burrowers and 4 aquatic species. Members of each of these 2 groups exhibited distinct microgeographic and microhabitat selection patterns, with several species showing non-overlapping microdistributions. We documented C. pyronotus from only 12 of 29 stream drainages surveyed, all within the middle region of the survey area, for a total range estimate of about 80 km2. Most of the inhabited streams within this small range occur on protected lands and include multiple habitable branches.

Habitat selection and partitioning of the Black-bellied Sandgrouse (Pterocles orientalis), the Stone Curlew (Burhinus oedicnemus) and the Cream-coloured Courser (Cursorius cursor) in arid areas of North Africa

Niche theory predicts that coexisting species with similar trophic requirements should demonstrate resource partitioning, particularly where resources are scarce. Conversely, this is not expected between species that do not share primary resources. This study analyses the patterns of spatial coexistence and habitat selection, on two spatial scales, of three species of semidesert regions in Morocco: the Black-bellied Sandgrouse (Pterocles orientalis), the Stone Curlew (Burhinus oedicnemus) and the Cream-coloured Courser (Cursorius cursor). Co-occurrence analysis results point to between-species segregation on a macrohabitat scale. Hotelling's T test of the species-presence data showed a pattern of macrohabitat selection that diverged from habitat availability for the three species with differences among them. Both the classification tree and the pattern of microhabitat selection obtained by model averaging showed scant overlap between the Sandgrouse and the Courser, suggesting habitat partitioning between them on a fine scale. Our results confirm spatial segregation of the three species, especially between species with different trophic strategies: the Sandgrouse versus the Stone Curlew and the Courser. The latter two species were best segregated on a microhabitat scale, supporting the conclusions that macro- and microhabitat selection are major factors in bird community configuration in arid ecosystems and contributing to reduce potential competition.

Habitat Use and Separation among Congeneric Darter Species

AbstractFive darter species (Greenside Darter Etheostoma blennioides, Rainbow Darter E. caeruleum, Fantail Darter E. flabellare, Johnny Darter E. nigrum, and Orangethroat Darter E. spectabile) were collected from seven streams and rivers in two Indiana watersheds to determine patterns of microhabitat selection with respect to depth, water velocity (flow), and substrate size. Heterogeneous habitats create a variety of niche dimensions, promoting the coexistence of congeneric species. Greenside and Rainbow darters were most commonly found among intermediate substrate sizes (cobble + boulder) and in locations with higher velocities and deeper water. Fantail and Orangethroat darters associated with intermediate to large substrate sizes (cobble + bedrock) were found in shallower water with lower velocities. Fantail Darters were only observed in the Whitewater River watershed. In contrast, Johnny Darters were observed only within the White River watershed among small substrate sizes (silt + sand), moderate velocities, and deeper water. Based on nonmetric multidimensional scaling and multinomial logistic regression, substrate size was the most important variable in characterizing microhabitat selection. Ultimately, habitats produced patterns of segregation and coexistence among these five darters in Indiana streams. Although ecological patterns of microhabitat use are additionally influenced by competition, morphology, and life history traits, heterogeneous habitat features within ecosystems appear to be structuring fish assemblages.

Winter home range and habitat use by porcupines in Alaska

AbstractHabitat selection results from trade‐offs between availability and use of resources under constraints of predation, competition, or other threats, which can vary spatially and temporally. For northern herbivores, winter food availability and quality can limit population size and may drive habitat preference. North American porcupines (Erethizon dorsatum) are widespread generalist herbivores that range from Mexico to the northern reaches of Alaska. During the long Alaskan winter, porcupines deal with high energetic demands resulting from low ambient temperatures while subsisting on low quality forage. We tracked free‐ranging porcupines over 3 winters in southcentral Alaska to determine habitat selection and home range size in relation to diet. Porcupines maintained larger than expected home ranges, and selected for conifer‐hardwood forests at the home range level. Individual variation among porcupines was too large to determine a pattern of microhabitat selection among trees. Regardless, direct observations revealed that porcupines used only white spruce and paper birch trees for foraging. White spruce may provide some nutritional and thermoregulatory advantage over paper birch; however, porcupines did feed on paper birch cambium, suggesting some nutritional requirement is met by eating paper birch. Porcupines most likely feed on paper birch cambium when detoxification pathways used to process plant toxins in white spruce needles are saturated. Maintaining mixed conifer‐hardwood forests in southcentral Alaska would provide suitable winter habitat for porcupines and may alleviate damage to single species stands of conifers or hardwoods that are preferred by commercial forestry operations. © 2012 The Wildlife Society.

Life begins when the sea lion is ashore: microhabitat use by a louse living on a diving mammal host

Among Anoplura, the family Echinophthiriidae includes species that infest pinnipeds and otters. Previous evidence obtained from pinnipeds infested by echinophthiriids, specifically from seals, indicates that flippers are the preferred infestation sites, while lice from fur seals select areas in the pelage. We studied habitat selection of Antarctophthirus microchir on South American sea lion pups (Otaria flavescens Shaw, 1800) from Patagonia, Argentina, during the austral summer of 2009. We found a clear pattern of habitat selection: eggs are laid on the dorsal surface; nymphs 1 hatch there and then migrate to the belly, where they develop into adults and copulate; and then ovigerous females return to the dorsal surface. On the one hand, nymphs 1 are characterised by their low locomotory ability; therefore, the fact that they migrate as soon as they hatch suggests a clear pressure leading to microhabitat restriction. On the other hand, the described pattern of microhabitat selection seems to respond to the physiological requirements of each stage, which vary according to the physiological process considered, e.g. oviposition, morphogenesis, hatching and development. Accordingly, it appears that A. microchir would prefer the host's ventral area for development and copulation and the dorsal area for oviposition. However, the causes of this pattern are not clear, and many factors could be involved. Considering that sea lion pups periodically soak at high tides, and that prolonged immersion and very high humidity are known to be lethal for lice eggs, selecting the dorsal area would be advantageous for oviposition because it dries much faster. Furthermore, because humidity should be retained for longer periods on the ventral surface of the pup, wetter conditions on the sea lion would prevent desiccation of the nymphs in the very arid environment where O. flavescens breeds.

Importance of seagrass vegetation for habitat partitioning between closely related species, mobile macrofauna Neomysis (Misidacea)

Seagrass meadows provide both habitats and a range of food sources for macrofaunal communities. These functions facilitate the coexistence of less mobile invertebrates (in comparison with mysids, such as amphipods) that are associated with seagrass leaves, and may also enhance the coexistence of highly mobile invertebrates such as mysid. We investigated the function of seagrass in supporting the coexistence of two mysid species, Neomysis awatschensis and N. mirabilis. These taxa are dominant in seagrass ecosystems of temperate coastal areas. We compared patterns of habitat use between the two species at mesoscales (among seagrass patches) and microscales (among seagrass leaves) by performing field surveys and laboratory experiments. The field survey results showed positive correlations in the abundance of the two mysid species, indicating that both species select similar habitats at the mesoscale level. In the laboratory experiments, the pattern of microhabitat selection (fundamental habitat) was similar for both species, even at increased densities and with the presence of an immobile habitat-competitor (the gastropod Barleeia angustata) on the leaves. However, this pattern changed significantly when a food source (epiphytic microalgae) was present on the leaves. This result indicates that (i) inter- and intraspecific interference competition does not affect microhabitat selection in these two mysids and (ii) both Neomysis species use similar habitats at the feeding stage. Although these two closely related mysids species may have similar requirements for microhabitat and food, the evidence that they did not act as competitors is attributable to unrestricted microhabitat and food (e.g., epiphytic algae) in the presence of seagrass vegetation.

Seasonal Microhabitat Selection by Terrestrial Rodents in an Old-Growth Atlantic Forest

We tested the hypothesis that microhabitat variables, abundance of terrestrial rodents, and microhabitat selection patterns of terrestrial rodents vary between the cool-dry and warm-wet season in the Atlantic forest of Brazil. We selected variables associated with ecological factors potentially important to terrestrial rodents (physical structure of litter and woody debris, and arthropod availability) and established 25 small, independent sampling units covering 36 ha of a homogenous, mature Atlantic forest patch. Litter humidity and height, amount of small woody debris, arthropod availability, and terrestrial rodent abundance increased, whereas the quantity of large woody debris decreased in the warm-wet season. Greater spatial segregation among terrestrial rodents also was observed in this season, especially between morphologically similar species. The distribution of 3 of the 4 most common terrestrial rodents was influenced by microhabitat variables in at least 1 of the seasons, and these species also differed in their pattern of microhabitat selection between seasons. In general, the amount of small woody debris and litter humidity were more important for the microscale distribution of terrestrial rodents in the cool-dry season, whereas in the mild warm-wet season species distributions were associated with food availability or were not clearly influenced by the measured variables. The patterns of microhabitat selection by 3 common terrestrial rodents, which were associated with features that characterize old-growth forest, may be responsible for their vulnerability to forest fragmentation.