Variation In Habitat Characteristics Research Articles

Temporal vs. spatial variation in stress-associated metabolites within a population of climate-sensitive small mammals.

ABSTRACTTemporal variation in stress might signify changes in an animal’s internal or external environment, while spatial variation in stress might signify variation in the quality of the habitats that individual animals experience. Habitat-induced variations in stress might be easiest to detect in highly territorial animals, and especially in species that do not take advantage of common strategies for modulating habitat-induced stress, such as migration (escape in space) or hibernation (escape in time). Spatial and temporal variation in response to potential stressors has received little study in wild animals, especially at scales appropriate for relating stress to specific habitat characteristics. Here, we use the American pika (Ochotona princeps), a territorial small mammal, to investigate stress response within and among territories. For individually territorial animals such as pikas, differences in habitat quality should lead to differences in stress exhibited by territory owners. We indexed stress using stress-associated hormone metabolites in feces collected non-invasively from pika territories every 2 weeks from June to September 2018. We hypothesized that differences in territory quality would lead to spatial differences in mean stress and that seasonal variation in physiology or the physical environment would lead to synchronous variation across territories through time. We used linear mixed-effects models to explore spatiotemporal variation in stress using fixed effects of day-of-year and broad habitat characteristics (elevation, aspect, site), as well as local variation in habitat characteristics hypothesized to affect territory quality for this saxicolous species (talus depth, clast size, available forage types). We found that temporal variation within territories was greater than spatial variation among territories, suggesting that shared seasonal stressors are more influential than differences in individual habitat quality. This approach could be used in other wildlife studies to refine our understanding of habitat quality and its effect on individual stress levels as a driver of population decline.

Influence of habitat composition on nestling body condition and breeding success in European Pied Flycatchers (Ficedula hypoleuca)

The vegetation structure surrounding nest sites is a crucial component of habitat quality and may have large effects on avian breeding performance. Habitat quality reflects the extent to which the environmental characteristics of an area correspond to the preferred habitat characteristics of the species. The concentration of haemoglobin is considered a simple biochemical indicator of nestling body condition. We present results concerning the effects of variation in habitat characteristics on the concentration of haemoglobin in the blood of 14-day-old nestlings and breeding success of European Pied Flycatchers ( Ficedula hypoleuca) in a mature mixed deciduous forest in central Poland. The haemoglobin concentration of nestlings was higher when there were more native oaks and deciduous, native trees on the territory. Breeding success was reduced by the number of alien oak (the Red Oak, Quercus rubra) and other alien deciduous trees, but increased by the number of native oaks in the territory. This study was conducted on only one site so further research is needed to examine the broader applicability of our results. Our data support the idea that haemoglobin concentration may serve as a simple indicator of body condition in nestlings and is useful in field ecophysiology studies of European Pied Flycatchers.

Relationships between Wildfire Burn Severity, Cavity-Nesting Bird Assemblages, and Habitat in an Eastern Ponderosa Pine Forest

Historically, eastern ponderosa pine (Pinus ponderosa) forests were described as sparse patches of old-growth trees maintained by frequent, low-severity fires; however, in recent decades, there have been a number of large mixed-severity wildfires throughout the range of these forests. Wildlife responses to severe fire disturbance in eastern ponderosa pine forests are not well understood. Our study investigates how cavity-nesting bird species in an eastern ponderosa pine forest are impacted by burn severity. The objectives of our study were to: (1) identify the community composition of cavity-nesting birds in a 27 y old burn of mixed severity, (2) assess how habitat variables important to cavity-nesting birds differ in the mixed-severity fire, and (3) determine what habitat variables best predict bird occurrence 27 y after mixed-severity fire. We surveyed 56 sites across four burn severity classes, ranging from unburned to severely burned forest, in the Pine Ridge region of Nebraska. We measured multiple habitat characteristics (tree and snag diameter at breast height (DBH), coarse woody debris (CWD), tree and snag density, shrub height, and shrub cover) in May–August 2016 and conducted bird count surveys between 25 May and 8 June 2016. Cavity-nesting bird species' occurrence varied among the burn severity variables. Burn severity class (unburned, low severity, moderate severity, high severity) was a significant predictor of habitat characteristics for cavity-nesting birds, including tree density, snag density, mean snag DBH, variance in DBH, and CWD, which also was the best indicator of cavity-nesting bird community composition. We report evidence that mixed-severity wildfires in eastern ponderosa pine forests create variation in habitat characteristics and cavity-nesting bird occurrence.

QPCR detection of Sturgeon chub (Macrhybopsis gelida) DNA in environmental samples.

The Sturgeon chub (Macrhybopsis gelida) is a cyprinid fish native to the Missouri and Mississippi River basins of the U.S. Suspected long-term declines in the size of its distribution have prompted a review of its conservation status by the U.S. Fish and Wildlife Service, a process which depends on reliable methods to delineate the distribution and status of extant populations. To facilitate monitoring of Sturgeon chub populations, we developed a quantitative PCR assay to detect Sturgeon chub DNA in environmental samples. The assay consistently detected Sturgeon chub DNA in concentrations as low as 2 copies per reaction, and did not amplify DNA from non-target fish species that are sympatric in the upper Missouri River basin. Field tests of this assay with environmental samples successfully detected Sturgeon chub from sites known to be occupied. This assay offers an extremely sensitive methodology that can be applied to determine the range of Sturgeon chub, regardless of variation in habitat characteristics.

Genetic diversity mirrors trophic ecology in coral reef fish feeding guilds

Genetic diversity is essential for species persistence because it provides the raw material for evolution. For marine organisms, short pelagic larval duration (PLD) and small population size are characteristics generally assumed to associate with low genetic diversity. The ecological diversity of organisms may also affect genetic diversity with an expected corollary that more restricted habitat and dietary requirements could lead to a reduced genetic diversity because of pronounced genetic structuring. Here, we tested whether groups of species with narrower trophic niches displayed lower genetic diversity than those with broader niches. In order to test those predictions, we used different trophic guilds (i.e., groups of species having similar trophic habits) of coral reef damselfishes in Moorea (French Polynesia) for which we determined their genetic diversity using restriction site-associated DNA sequencing (RADseq) and their trophic ecology with stomach contents and stable isotope data. We found that pelagic feeders- the guild picking zooplankton in the water column- exhibited the lowest genetic diversity despite having the longest PLD and the largest population size. This guild had also the lowest variation in habitat characteristics and dietary composition compared to benthic feeders (i.e., those mainly grazing on algae) and the intermediate group (i.e., those feeding on zooplankton, filamentous algae and small benthic invertebrates). Our findings highlight the association between trophic ecology and genetic diversity that should be more commonly investigated in population genetics.

Time since disturbance affects colonization dynamics in a metapopulation.

Disturbances are widespread in nature and can have substantial population-level consequences. Most empirical studies on the effects of disturbance track population recovery within habitat patches, but have an incomplete representation of the recolonization process. In addition, recent metapopulation models represent post-disturbance colonization with a recovery state or time-lag for disturbed ("focal") patches, thus assuming that recolonization rates are uniform. However, the availability of colonists in neighbouring "source" patches can vary, especially in frequently disturbed landscapes such as fire-managed forests that have a mosaic of patches that differ in successional state and undergo frequent local extinctions. To determine how time since disturbance in both focal and neighbouring source patches might affect metapopulations, we studied the effects of time since fire (TSF) on abundances of a specialist palmetto beetle within and between fire management units in Apalachicola National Forest, Florida. We measured beetle abundances at three distances from the shared edge of paired units, with units ranging from 0 to 64months since fire and the difference in time since burning for a focal-source pair ranging from 3 to 58months. Soon after fire, beetle abundances within management units were highest near the unit edge, but this pattern changed with increasing TSF. Between paired units, the more recently disturbed ("focal") unit's beetle abundance was positively related to source unit abundance, but the shape of this relationship differed based on focal unit TSF and the units' difference in time since burning. Results suggest that both focal and source habitat history can influence recolonization of recently disturbed patches and that these effects may persist over years. Thus, when predicting metapopulation dynamics, variation in habitat characteristics should be considered not only for patches receiving colonists but for patches supplying colonists as well.

Spatial and temporal variation in macroparasite communities of three-spined stickleback.

Patterns in parasite community structure are often observed in natural systems and an important question in parasite ecology is whether such patterns are repeatable across time and space. Field studies commonly look at spatial or temporal repeatability of patterns, but they are rarely investigated in conjunction. We use a large dataset on the macroparasites of the three-spined stickleback, Gasterosteus aculeatus L., collected from 14 locations on North Uist, Scotland over an 8-year period to investigate: (1) repeatability of patterns in parasite communities among populations and whether variation is consistent across years, (2) whether variation between years can be explained by climatic variation and progression of the season and (3) whether variation in habitat characteristics explain population differences. Differences in relative abundance and prevalence across populations were observed in a number of parasites investigated indicating a lack of consistency across years in numerous parasite community measures; however, differences between populations in the prevalence and abundance of some parasites were consistent throughout the study. Average temperature did not affect parasite community, and progression of the season was only significant for two of 13 community measures. Two of the six habitat characteristics investigated (pH and calcium concentration) significantly affected parasite presence.

Birds and butterflies respond to soil‐induced habitat heterogeneity in experimental plantings of tallgrass prairie species managed as agroenergy crops in Iowa, USA

Summary The maintenance of habitat heterogeneity in agricultural landscapes has been promoted as a key strategy to conserve biodiversity. Animal response to grassland heterogeneity resulting from spatiotemporal variation in disturbance is well documented; however, the degree to which edaphic variation generates heterogeneity detectable by grassland wildlife has proven more difficult to study in natural settings. We conducted a field experiment to study how soils directly affect vegetation structure and composition and indirectly affect bird and butterfly assemblages using plantings of tallgrass prairie species managed as agroenergy crops in Iowa, USA. The experimental design included four vegetation treatments of varying species richness replicated on three soil types. Habitat characteristics varied widely among soils. Crops on sandy loam, the driest, most acidic soil with the lowest nutrient content, developed shorter, less dense vegetation with sparse litter accumulation and more bare ground compared to crops on loam and clay loam. Birds and butterflies responded similarly to soil‐induced variation in habitat characteristics. Their abundance and species richness were similar on all soils, but their assemblage compositions varied among soils in certain vegetation treatments. In low‐diversity grass crops, bird assemblages using sandy loam were dominated by species preferring open ground and sparse vegetation for foraging and nesting, whereas assemblages using loam and clay loam were dominated by birds preferring tall, dense vegetation with abundant litter. In high‐diversity prairie crops, the species composition of forbs in bloom varied among soils and strongly influenced butterfly assemblages. Synthesis and applications. Prairie agroenergy crops established with identical management practices developed variable habitat characteristics due to natural edaphic variation, and this heterogeneity influenced the spatial distribution of bird and butterfly assemblages due to differential habitat use among species. This finding suggests that if unfertilized prairie crops were grown for agroenergy by land managers large‐scale, soil‐induced habitat heterogeneity would promote wildlife diversity within and among fields, further increasing the habitat value of these crops compared to the fertilized, annual monocultures that currently dominate the agricultural landscape. Our study also highlights the need for managers to consider soil properties when selecting sites to restore grassland habitat for species of conservation concern.

Using species traits to assess human impacts on near shore benthic ecosystems in the Canadian Arctic

Human activities have the potential to alter the diversity and composition of biological communities in natural environments, which can cause changes in ecosystem functioning. This has led to the development of environmental assessment techniques that take into account species identity, as species can contribute differently to various ecosystem processes. Biological Traits Analysis (BTA) is used to compare the abundances of specific biological traits in samples to produce information about how ecosystem functioning may change across a specific terrestrial or aquatic system. In the present study, BTA was used to assess the influence of municipal wastewater effluent on benthic marine communities in near shore soft sediments in four locations across the Canadian Arctic Territory of Nunavut, Canada. Shifts in trait composition were assessed relative to indicators of sediment enrichment (sediment chlorophyll, organic content, degree of anoxia), and natural variation in habitat characteristics (water depth, porosity, average grain size) at a site receiving wastewater and a reference site in each sampling location. The results indicated a mild enrichment effect of wastewater, as evidenced by changes in trait composition at three of the four sites that received wastewater inputs. However, the amount of variance in trait composition explained by metrics of wastewater enrichment in these locations were generally equal to or lower than the amount of variance explained by sediment characteristics related to natural processes. These results provide greater insight into the underlying causes and consequences of human activities than more traditional methods for environmental impact assessment, and can be directly applied in a management context.

Fine‐scale habitat use during the non‐breeding season suggests that winter habitat does not limit breeding populations of a declining long‐distance Palearctic migrant

For migrant birds, which habitats are suitable during the non‐breeding season influences habitat availability, population resilience to habitat loss, and ultimately survival. Consequently, habitat preferences during winter and whether habitat segregation according to age and sex occurs directly influences migration ecology, survival and breeding success. We tested the fine‐scale habitat preferences of a declining Palearctic migrant, the whinchatSaxicola rubetra, on its wintering grounds in west Africa. We explored the influence of habitat at the territory‐scale and whether dominance‐based habitat occupancy occurs by describing the variation in habitat characteristics across wintering territories, the degree of habitat change within territories held throughout winter, and whether habitat characteristics influenced territory size and space‐use within territories or differed with age and sex. Habitat characteristics varied substantially across territories and birds maintained the same territories even though habitat changed significantly throughout winter. We found no evidence of dominance‐based habitat occupancy; instead, territories were smaller if they contained more perching shrubs or maize crops, and areas with more perching shrubs were used more often within territories, likely because perches are important for foraging and territory defence. Our findings suggest that whinchats have non‐specialised habitat requirements within their wintering habitat of open savannah and farmland, and respond to habitat variation by adjusting territory size and space‐use within their territories instead of competing with conspecifics. Whinchats show a tolerance for human‐modified habitats and results support previous findings that some crop types may provide high‐quality wintering habitat by increasing perch density and foraging opportunities. By having non‐specialised requirements within broad winter habitat types, migrants are likely to be flexible to changing wintering conditions in Africa, both within and across winters, so possibly engendering some resilience to the rapid anthropogenic habitat degradation occurring throughout their wintering range.

Variation in Habitat Characteristics of American Pikas along an Elevation Gradient at Their Northern Range Margin

Temperature is an important environmental variable in shaping the distribution of species. The American pika (Ochotona princeps) has been identified as a climate-change-sensitive species as documented by the extirpation of a number of populations at the southern end of the species' range. Limited tolerance to warm temperatures has previously been reported, yet recent evidence suggests that pikas are able to live outside of cool habitats with the discovery of warmer, low-elevation pika populations, such as those found in the Bella Coola Valley in British Columbia. Here we characterize the temperatures experienced by pikas living along an elevation gradient at the northern end of their distribution. Additionally, we recorded temperatures both above and below the talus at one of our sites and the relationship between pika activity and temperature. Temperatures differed along the elevation gradient by up to 6 °C from low- to high-elevation sites. Below-talus temperatures were lower than above-talus temperatures at noon and during the afternoon, and were warmer than above temperatures in the morning and night, suggesting that talus has insulative properties that guard against extreme temperatures. Lastly, a negative relationship was observed between temperature and pika activity. We show that although at the northern end of pika distribution, ambient temperatures 1.5 m above the talus surface often exceeded the threshold for acute heat stress. Our results also suggest that behavioral thermoregulation or other adaptations may enable pikas to inhabit low-elevation habitat that was previously thought as inhospitable to pikas.

Variation in habitat characteristics and the occurrence of Nothobranchius species in seasonal biotopes of Tanzania

Variation in habitat characteristics and the occurrence of Nothobranchius species in seasonal biotopes of Tanzania

Habitat variation influences movement rates and population structure of an intertidal fish

Understanding how variation in habitat characteristics influences the demography and behavior of organisms is of primary interest in ecological research. I studied how patterns of distribution, abundance, mortality and movement of the fluffy sculpin, Oligocottus snyderi, are related to variation in habitat characteristics within and between sites. The recruitment levels of O. snyderi are very similar at two different intertidal sites, yet post-recruitment processes modify the original recruitment signal at only one of the two sites. The two sites differ significantly in only one measured aspect of their tidepool habitat-the amount of cover provided by surfgrass or algae. Both recruits and adults of O. snyderi exhibit positive associations with the amount of tidepool cover, particularly the presence of surfgrass. A mark-recapture study determined that these differences in the habitat characteristics between the two sites are associated with differences in post-recruitment movement rates. In fact, the absence of a correlation at one site between O. snyderi recruit and adult abundances, which would typically be considered evidence for significant post-recruitment mortality, appears to be driven by strong within-site post-recruitment movement. Furthermore, although post-recruitment mortality rates do not vary significantly across the two sites, variation in post-recruitment mortality is weakly related to within-site variation in tidepool characteristics at one site. The results of this study suggest that post-settlement intertidal fishes continue to sample their surrounding environment as they mature and will redistribute themselves according to within-site spatial variation in habitat characteristics-a behavioral process that may obscure estimates of post-settlement mortality.

Evaluating the Effects of Habitat Patchiness on Small Fish Assemblages in a Great Lakes Coastal Marsh

Wetlands are naturally heterogeneous ecosystems with resident species adapted to patchy environments. We measured how assemblages of small fish varied among four natural patches of coastal marsh in Mismer Bay, Lake Huron, USA. We sampled patches continuously for extensive time periods to describe both spatial and temporal fish distribution patterns. Fish richness and distribution varied spatially with some species restricted to one or two patches, such as Phoxinus eos and Margariscus margarita, and others widely distributed, such as Pimephales notatus and Culaea inconstans. For ubiquitous species, patch utilization varied temporally, which was explained by variation in habitat characteristics, such as macrophyte richness and growth form diversity, emergent macrophyte stem density, water temperature and depth. Northern Great Lakes coastal marshes are not static environments, and intensive sampling illustrates the dynamic interactions between fishes and this successional marsh environment. We conclude that extended sampling protocols in patchy, temperate wetlands are preferable to short surveys for making accurate evaluations about the spatio-temporal habitat utilization of fishes.

Seasonal Variation in Fish Assemblage Structure and Habitat Structure in the Nearshore Littoral Zone of Wisconsin Lakes

To evaluate whether fish abundance, fish habitat, and fish–habitat associations vary across seasons in nearshore littoral zones of five northern Wisconsin lakes, we assessed fish abundances and quantified habitat characteristics in littoral zones across three seasons (spring, summer, and fall) during 1996. Seasonal responses of the fish community in the nearshore littoral zone were taxa specific and guild specific. In the nearshore littoral zone, species richness and the abundance of pumpkinseeds Lepomis gibbosus, rock bass Ambloplites rupestris, yellow perch Perca flavescens, and centrarchids differed significantly across seasons. Some habitat characteristics, including mean water depth, maximum water depth, percent floating vegetation, and percent submersed vegetation, also differed significantly among seasons. Analysis of covariance indicated that changes in fish abundance for the three species coincided with variation in habitat characteristics in the nearshore littoral zone. Significant interactions (i.e., season × habitat characteristic) in the analyses suggest that some individual species responses to habitat variation were dependent upon seasons. However, despite some seasonal differences in fish assemblage structure, we also observed consistent fish–habitat associations for many fish species, regardless of season. Moreover, for the purpose of characterizing littoral zone fish communities and fish–habitat associations, it appears that sampling for most species can be done at any time from spring to early fall. However, evaluation of the effects of habitat modifications on fish assemblages should take into account the natural seasonal changes in abundance associated with changes in macrophyte growth and changing water levels.

Fish Assemblage Stability in a Southern Appalachian Stream

We monitored fish populations at three sites in a southern Appalachian stream system during a 40-mo study. Assemblages at two sites, consisting of four and five resident species, were persistent in terms of relative species abundances and production. This persistence was related to low variation in abundance of the two numerically dominant fishes, mottled sculpins (Cottus bairdi) and longnose dace (Rhinichthys cataractae). Less abundant residents, rosyside dace (Clinostomus funduloides), rainbow trout (Salmo gairdneri), and greenside darters (Etheostoma blennioides), displayed lower levels of persistence. We also observed pronounced annual variation in either young-of-the-year recruitment and/or subsequent year-class strength of four resident species, possibly resulting from a severe drought during the third year of study. Abundance and production of rosyside dace and trout were greatly affected by fluctuations in recruitment and year-class strength, suggesting that environmental variability strongly influenced these populations. Density-dependent mechanisms may have regulated sculpin and longnose dace populations. The three-species asssemblage at a third site also was persistent as a result of relatively stable sculpin and longnose dace populations, whereas the rainbow trout population fluctuated among years. We observed significant intersite differences in relative year-class strength in a given year and in population structures of sculpins and longnose dace, suggesting that spatial variation in habitat characteristics affected assemblage dynamics and responses to environmental fluctuations.

Sympatry and allopatry of song in North American tanagers

The possibility that the hypotheses of character convergence and character displacement might explain interspecific variation in song features among North American tanagers is examined. Scarlet and summer tanagers (Piranga olivacea and P. rubra) are the most sympatric among the four species and have the largest differences in song characteristics. However, songs of scarlet tanagers do not differ significantly between sympatry and allopatry. Songs of summer tanagers more resemble those of scarlet tanagers in allopatry, but this geographical variation has been explained by variation in habitat characteristics. Both species countersing in sympatry, and react aggressively to each other's songs in sympatry as well as in allopatry, probably due to similarities in the song. The limited data from the narrow sympatric zone between western and hepatic tanagers (P. ludoviciana and P. flava) indicate that their songs differ to a great extent. Therefore, the results do not support the hypothesis of character convergence. Character displacement might explain partially interspecific differences in song features between scarlet and summer tanagers but cannot be tested further.