Variation In Habitat Structure Research Articles

Seasonal variability in habitat structure may have shaped acoustic signals and repertoires in the black-capped and boreal chickadees

Many songbird species have evolved multiple vocalizations, or repertoires, that function to communicate various biological signals. More diverse repertoires may have evolved in response to the effects of seasonal variation in habitat structure on signal transmission. Such changes in habitat necessarily occur for migrating species, but they also occur for resident species that occupy deciduous forests. The black-capped chickadee (Poecile atricapillus) possesses a chick-a-dee call and a fee-bee song, but the closely related boreal chickadee (P. borealis) lacks a song. Consistent with the habitat variability hypothesis, the black-capped chickadee possesses a larger repertoire and primarily occupies deciduous forests, whereas the songless boreal chickadee occurs more often in coniferous forests. We explored the ecological basis of this hypothesis by recording audio playbacks of two species in two habitat types during two seasons. Specifically, we played both songs and calls of the black-capped chickadee and calls of the boreal chickadee in deciduous and coniferous habitats, prior to and after leaf-out. We measured attenuation and degradation in re-recorded vocalizations. For black-capped chickadees, the song was less degraded than the call in post-leaf, deciduous forests. The boreal chickadee call attenuated more quickly in all treatments, but maintained its acoustic structure better than both black-capped chickadee vocalizations in coniferous forests. Our results support the hypothesis that variable habitats provided a seasonal transmission benefit for both song and call in the black-capped chickadee, but that the transmission benefit of song is lost in the less variant coniferous forests, which may underlie the absence of a song in the boreal chickadee.

Urbanization impacts on the trophic guild composition of bird communities

ABSTRACTUrbanization transforms the landscape and generates loss of pristine habitats. We investigated the urbanization effect on bird communities in a growing South American city (Santa Fe, Argentina) and hypothesized that if habitat structure and human disturbance change along an urban gradient, the richness and abundance of trophic guilds should also vary accordingly. We placed 50 transects 100 m long × 50 m wide in five districts with different levels of urbanization, determined by habitat structure variables. We recorded the number and abundance of species and the amount of pedestrians and vehicles passing through each transect. We recorded 23% of all bird species known for the Santa Fe province and categorized them within 19 trophic guilds. The percentage of area covered by herbaceous vegetation, water bodies and trees and shrubs had a positive relationship with the richness and abundance of most of trophic guilds (hawking aerial, terrestrial, bark and foliage insectivores; terrestrial and generalized granivores; generalized, aquatic diving and foliage omnivores; hawking aerial, aquatic diving and striding carnivores; nectarivores; and aquatic filters). Pavement surface and human disturbance variables had a negative relationship with the richness, and high buildings and pavement surface had a positive relationship with the abundance of terrestrial omnivores and coursing aerial insectivores. Variation partitioning revealed that habitat structure and human disturbance were better predictors of the richness than the abundance of each trophic guild. Results showed that trophic guilds associated to vegetation strata were seen to increase their richness and abundance towards green areas, even if they presented generalist or specialist habits. Urban planners should conserve or manage the surrounded natural spaces when the growth of the city is directed to these areas and increase the availability of environmental features within the urban matrix.

Disentangling spatial and environmental determinants of fish species richness and assemblage structure in Neotropical rainforest streams

Abstract Freshwater ecology templates were developed in temperate streams, but whether they also apply to tropical streams that harbour a higher biological diversity than their temperate counterparts remains uncertain. This is particularly true for tropical fish assemblages inhabiting small streams that have been less studied than larger, higher‐order lowland streams. Here, we disentangled the strength of spatial (longitudinal and environmental) drivers, and scale‐specific (drainage basin, reach and local scale) determinants of species richness and composition of freshwater fish assemblages inhabiting small streams in French Guiana. We found that species richness increased from upstream to downstream but also with increasing local habitat structural diversity independently of stream position in the upstream–downstream gradient. This pattern was shared by the two most speciose fish orders (Characiformes and Siluriformes), demonstrating that species addition rather than species replacement shaped species richness in these assemblages. Species composition of fish assemblages was determined equally by their spatial structure within drainage and by the environment, and assemblages differed both with distance and along an upstream–downstream gradient. The environmental effect on species assemblages indicated by the fact that almost all environmental descriptors had slight but nonetheless significant effects on assemblage composition, probably reflecting species‐specific responses to the local environment. In contrast, despite a strong micro‐endemism between drainages for some taxa, assemblages were only slightly affected by river drainage identity, since widespread species were a common constituent of assemblages in all rivers. We identified five species assemblages characterising different local habitat features from torrential areas to lowland muddy areas. We also distinguished fish assemblages from confluence areas with larger rivers, which differed from the other five assemblages. The fish zonation patterns we report can constitute a benchmark for future studies measuring the impact of anthropogenic disturbances on Neotropical forest streams.

Remotely sensed forest habitat structures improve regional species conservation

AbstractRecent studies show that light detection and ranging (LiDAR) derived habitat variables significantly increase the performance and accuracy of species distribution models (SDMs). In particular, the structure of complex habitats such as forest can be accurately parametrized by an area‐wide, LiDAR‐based vegetation profile. However, evidence of specific applications of such models in real‐world conservation management still remains sparse. Here, we developed a resource selection SDM for hazel grouse (Bonasa bonasia L.) in a Swiss nature park with the aim to map habitat suitability and to inform the park management about habitat improvement measures. We used remote sensing, particularly LiDAR to derive ecologically relevant forest vegetation characteristics at the local scale and used them as predictors in an ensemble SDM approach. The predicted habitat suitability was mainly affected by local, fine grained vegetation structure. Average vegetation height, shrub density and canopy height variation contributed most to the habitat quality for hazel grouse. This clearly shows how LiDAR provides the means to develop ecologically interpretable predictor variables of forest habitat structure and that these predictors can be used to reliably map local‐scale habitat quality, indicated by high model performance scores (median AUC of 0.918). This improves spatial conservation planning, and at the same time, provides meaningful information to derive habitat improvement measures that can be implemented in the field by foresters. Hazel grouse occurrence in the park is restricted to a few highly suitable, disjunct habitat patches. Therefore, conservation management should increase the connectivity of suitable habitat with the aim to stimulate an increase and better exchange of individuals in the regional hazel grouse population. Habitat improvements can be achieved by forestry measures that regularly integrate early successional forest stages into production forests. They should contain stands with a shrub density of around 30% as well as heterogeneous stands in terms of vegetation height.

Efecto de los estadios sucesionales del bosque tropical seco sobre el microhabitat usado por Agalychnis dacnicolor (Anura: Phyllomedusidae) y Smilisca fodiens (Anura: Hylidae)

Habitat disturbance can modify microhabitats and therefore have a significant effect on the abundance and distribution of anurans species, particularly those associated to specific microhabitats. In this study we evaluated changes in the use of microhabitat by two syntopic species of tree frogs, Agalychnis dacnicolor and Smilisca fodiens along a successional gradient of Tropical Dry Forest in the region of the Biosphere Reserve of Chamela-Cuixmala at the coast of Jalisco, Mexico. We hypothesized that because these two species are habitat generalists, microhabitat use would change in response to secondary forest succession and to the climatic season of the year. Although both species were registered in both secondary and mature forests, A. dacnicolor was associated to mature forest, whereas S. fodiens was more associated to disturbed sites. Neither species showed differences in biomass among successional stages (ES) or between climatic seasons. Unlike S. fodiens, A. dacnicolor presented larger sizes during the rainy season. Body temperature of both species varied between ES and climatic season. S. fodiens presented a more constant temperature among individuals in pastures, while A. dacnicolor in mature forests. Environmental and structural habitat variables that influenced the presence of both species in ES were substrate temperature, height of tree or shrub where the frog was perching and percentage cover of litter, grasses, shrubs, trees and bare soil. The variables that best explained biomass, snout-vent length (LHC) and body temperature of S. fodiens were cover of dry branches and substrate temperature, whereas biomass of A. dacnicolor was better explained by cover of herbs, LHC, height of the tree or shrub where the frog was perching, body temperature and the substrate temperature. Both species used differentially environmental and structural variables of microhabitats along the gradient of initial to late ES. The variables that separated the species were the height of the shelter or perch and the percentage of trees in different ES. Whereas A. dacnicolor was more associated to the lowest strata of vegetation, S. fodiens showed plasticity in microhabitat use, especially in height of shelter or perch. Our results suggested that even when both species are considered habitat generalists, in anthropic landscapes, A. dacnicolor is specialist in microhabitat use, whereas S. fodiens is a species with greater ecological plasticity in microhabitat use. These differences in microhabitat use in response to habitat disturbance may help explain the success of these species in these new landscapes, as well as the importance of secondary forests in different stages of succession to maintain adequate microhabitats for the permanence of species in anthropogenic landscapes.

Diversity and composition of plants, butterflies and odonates in an Imperata cylindrica grassland landscape in East Kalimantan, Indonesia

Abstract:In Indonesia and elsewhere, Imperata cylindrica grassland now covers millions of hectares of land previously covered by rain forest. In the present study, shrubs, trees and climbers were recorded in sixteen 10 × 20-m plots and herb cover (ferns, grasses and herbaceous dicots) estimated in nested 2 × 2-m subplots. Butterflies and odonates were netted along 300-m transects. All plots and transects were randomly allocated to a 450 ha, I. cylindrica-dominated landscape. A total of 43 shrub, tree and climber, 16 herb, 67 butterfly and 30 odonate species were recorded. Shrubs, trees and climbers were present throughout the study area, but basal area was very low and mainly consisted of invasive species. Imperata cylindrica covered an estimated 65% of the area with other plant species or bare soil covering the remainder. Butterfly and odonate communities mainly consisted of species with large geographic distributions, but some recorded species had more limited distributions. The latter were, however, species known to associate with perturbed forest environments. Variation in the composition of butterflies and odonates was also related to variation in habitat structure (e.g. altitude and slope) and plant composition. Plant composition in particular appeared to structure both butterfly and odonate communities.

Effects of Grazing Management and Cattle on Aquatic Habitat Use by the Anuran Pseudopaludicola mystacalis in Agro-Savannah Landscapes

Because of their strong dependence on the environment, the spatial distribution of pond-breeding amphibians can be greatly influenced by anthropogenic habitat alteration. In some agricultural landscapes in Brazil, the anuran Pseudopaludicola mystacalis appears to be highly influenced by land use. Because adult males and tadpoles of this species are usually found in marshy areas with cattle hoof prints, we hypothesized that P. mystacalis preferentially occupies aquatic habitats with marshy areas that are trampled by cattle. To test our hypothesis, we assessed whether the occurrence of P. mystacalis is associated with the presence of cattle and trampled marshy areas, and which environmental features best explain the spatial distribution and abundance of P. mystacalis. To do so, we sampled 38 aquatic habitats in an area intensely used for livestock in southeastern Brazil. We found that the presence of cattle and trampled marshy areas in aquatic habitats are positively associated to P. mystacalis occurrence. Additionally, the abundance of calling males is better predicted by variables of landscape and local habitat structure. Specifically, the size of trampled marshy areas and the proportion of herbaceous vegetation within the aquatic habitat are positively associated with abundance, while distance to nearest aquatic habitat are negatively associated with abundance of calling males. All three of these variables can be directly or indirectly linked to the presence of cattle or grazing management. Therefore, this work shows evidence that Pseudopaludicola mystacalis is positively influenced by grazing management with cattle, and draws attention to other unknown potential consequences of different land use to fresh water diversity.

Meter scale variation in shrub dominance and soil moisture structure Arctic arthropod communities.

The Arctic is warming at twice the rate of the rest of the world. This impacts Arctic species both directly, through increased temperatures, and indirectly, through structural changes in their habitats. Species are expected to exhibit idiosyncratic responses to structural change, which calls for detailed investigations at the species and community level. Here, we investigate how arthropod assemblages of spiders and beetles respond to variation in habitat structure at small spatial scales. We sampled transitions in shrub dominance and soil moisture between three different habitats (fen, dwarf shrub heath, and tall shrub tundra) at three different sites along a fjord gradient in southwest Greenland, using yellow pitfall cups. We identified 2,547 individuals belonging to 47 species. We used species richness estimation, indicator species analysis and latent variable modeling to examine differences in arthropod community structure in response to habitat variation at local (within site) and regional scales (between sites). We estimated species responses to the environment by fitting species-specific generalized linear models with environmental covariates. Species assemblages were segregated at the habitat and site level. Each habitat hosted significant indicator species, and species richness and diversity were significantly lower in fen habitats. Assemblage patterns were significantly linked to changes in soil moisture and vegetation height, as well as geographic location. We show that meter-scale variation among habitats affects arthropod community structure, supporting the notion that the Arctic tundra is a heterogeneous environment. To gain sufficient insight into temporal biodiversity change, we require studies of species distributions detailing species habitat preferences.

Does ecophysiology mediate reptile responses to fire regimes? Evidence from Iberian lizards.

Background. Reptiles are sensitive to habitat disturbance induced by wildfires but species frequently show opposing responses. Functional causes of such variability have been scarcely explored. In the northernmost limit of the Mediterranean bioregion, lizard species of Mediterranean affinity (Psammodromus algirus and Podarcis guadarramae) increase in abundance in burnt areas whereas Atlantic species (Lacerta schreiberi and Podarcis bocagei) decrease. Timon lepidus, the largest Mediterranean lizard in the region, shows mixed responses depending on the locality and fire history. We tested whether such interspecific differences are of a functional nature, namely, if ecophysiological traits may determine lizard response to fire. Based on the variation in habitat structure between burnt and unburnt sites, we hypothesise that Mediterranean species, which increase density in open habitats promoted by frequent fire regimes, should be more thermophile and suffer lower water losses than Atlantic species.Methods. We submitted 6–10 adult males of the five species to standard experiments for assessing preferred body temperatures (Tp) and evaporativewater loss rates (EWL), and examined the variation among species and along time by means of repeated-measures AN(C)OVAs.Results. Results only partially supported our initial expectations, since the medium-sized P. algirus clearly attained higher Tp and lower EWL. The two small wall lizards (P. bocagei and P. guadarramae) displayed low Tp and high EWL while the two large green lizards (T. lepidus and L. schreiberi) displayed intermediate values for both parameters.Discussion. The predicted differences according to the biogeographic affinities within each pair were not fully confirmed. We conclude that ecophysiology may help to understand functional reptile responses to fire but other biological traits are also to be considered.

Does variable stand structure associated with multi-cohort forests support diversity of ground beetle (Coleoptera, Carabidae) communities in the central Nearctic boreal forest?

Multi-cohort management (MCM) that retains a range of stand structures (age and size class) has been proposed to emulate natural disturbance and improve management in the Nearctic boreal forest. Although MCM forests contain both single- and multi-aged stands of mixed tree sizes, little is known about how variable stand structure affects associated fauna and biodiversity. Here, we examine the relationship between ground beetle (Coleoptera, Carabidae) communities and stand characteristics across a range of forest structure (=cohort classes). Given that MCM classes are defined by the distribution of their tree–stem diameters, we ask whether parameters associated with these distributions (Weibull) could explain observed variation in carabid communities, and if so, how this compares to traditional habitat variables such as stand age, foliage complexity or volume of downed woody debris. We sampled carabids using weekly pitfall collections and compared these with structural habitat variables across a range of cohort classes (stand structure and age since disturbance) in 18 sites of upland mixed boreal forests from central Canada. Results showed that richness and diversity of carabid communities were similar among cohort classes. Weibull parameters from the diameter distribution of all stems were the strongest predictors of variation in carabid communities among sites, but vertical foliage complexity, understory thickness, and percentage of deciduous composition were also significant. The abundance of several carabid forest specialists was strongly correlated with tree canopy height, the presence of large trees, and high vertical foliage complexity. Our results demonstrate that variable forest structure, as expected under MCM, may be useful in retaining the natural range of ground beetle species across the central Nearctic boreal forest.

Birds as surrogates for mammals and reptiles: Are patterns of cross-taxonomic associations stable over time in a human-modified landscape?

Cross-taxonomic surrogates can be feasible alternatives to direct measurements of biodiversity in conservation if validated with robust data and used with explicit goals. However, few studies of cross-taxonomic surrogates have examined how temporal changes in composition or richness in one taxon can drive variation in concordant patterns of diversity in another taxon, particularly in a dynamic and heavily modified landscape. We examined this problem by assessing changes in cross-taxonomic associations over time between the surrogate (birds) and target vertebrate taxa (mammals, reptiles) that demand high sampling effort, in a heterogeneous mosaic landscape comprising pine monoculture, eucalypt woodland remnants and agricultural land. Focussing on four study years (1999, 2001, 2011, 2013) from a dataset spanning 15 years, we: (1) investigated temporal changes in cross-taxonomic congruency among three animal taxa, (2) explored how temporal variation in composition and species richness of each taxon might account for variation in cross-taxonomic congruency, and (3) identified habitat structural variables that are strongly correlated with species composition of each taxon. We found the strength of cross-taxonomic congruency varied between taxa in response to both landscape context and over time. Among the three taxa, overall correlations were weak but were consistently positive and strongest between birds and mammals, while correlations involving reptiles were usually weak and negative. We also found that stronger species richness and composition correlations between birds and mammals were not only more prevalent in woodland remnants in the agricultural matrix, but they also increased in strength over time. Temporal shifts in species composition differed in rate and extent among the taxa even though these changes were significant over time, while important habitat structural correlates were seldom shared across taxa. Our study highlights the role of the landscape matrix and time in shaping animal communities and the resulting cross-taxonomic associations in the woodland remnants, especially after a major perturbation event (i.e. plantation establishment). In such dynamic landscapes, differing and taxon-specific shifts in diversity over time can influence the strength, direction and consistency of cross-taxonomic correlations, therefore posing a ‘temporal’ problem for the use of surrogates like birds in monitoring and assessments of biodiversity, and conservation management practices.

Predicting faunal fire responses in heterogeneous landscapes: the role of habitat structure.

Predicting the effects of fire on biota is important for biodiversity conservation in fire-prone landscapes. Time since fire is often used to predict the occurrence of fauna, yet for many species, it is a surrogate variable and it is temporal change in resource availability to which animals actually respond. Therefore prediction of fire-fauna relationships will be uncertain if time since fire is not strongly related to resources. In this study, we used a space-for-time substitution across a large diverse landscape to investigate interrelationships between the occurrence of ground-dwelling mammals, time since fire, and structural resources. We predicted that much variation in habitat structure would remain unexplained by time since fire and that habitat structure would predict species' occurrence better than time since fire. In line with predictions, we found that time since fire was moderately correlated with habitat structure yet was a poor surrogate for mammal occurrence. Variables representing habitat structure were better predictors of occurrence than time since fire for all species considered. Our results suggest that time since fire is unlikely to be a useful surrogate for ground-dwelling mammals in heterogeneous landscapes. Faunal conservation in fire-prone landscapes will benefit from a combined understanding of fauna-resource relationships and the ways in which fire (including planned fires and wildfires) alters the spatial and temporal distribution of faunal resources.

<b>Habitat structure determining the spatial distribution of ichthyofauna in a Brazilian stream

This work aimed to evaluate the relationship between parameters of fish communities and the habitat structure of a stream. Twenty three stretches six meters long were evaluated in the Samambaia stream located inside the Sumidouro Park, Rio das Velhas basin, state of Minas Gerais, Brazil. Fish samplings and habitat characterization were made for each stretch. Seven variables of habitat (vegetal cover, width, depth, substrate, flow, presence of aquatic plants and leaf litter) and two variables characterizing the longitudinal gradient (altitude and distance from the Sumidouro lagoon) were assessed. The fish community responded to habitat changes, presenting variation in richness and composition of species. Richness was positively influenced by the presence of leaf litter and aquatic plants. Furthermore, through similarity data (NMDS) and habitat structure (PCA), it was possible to observe the separation of the 23 stretches into two groups with a dissimilarity of approximately 90%. We concluded that the variation in richness and composition of species throughout the stream was strongly related to the variables of habitat structure. This variation is clearer when considering the longitudinal gradient which highlights a great difference between stretches nearer and farther from the mouth of Samambaia stream.

Contrasts in short- and long-term responses of Mediterranean reptile species to fire and habitat structure.

Changes in habitat structure constitute a major factor explaining responses of reptiles to fire. However, few studies have examined habitat factors that covary with fire-history variables to explain reptile responses. We hypothesise that more complex habitats should support richer reptile communities, and that species-specific relative abundance should be related to particular habitat features. From spring 2012-2014, twenty-five transects were surveyed in the Albera Region (north-east Iberia). The vegetation structure was measured and the extent of habitat types in a 1000-m buffer around each transect calculated. Reptile-community metrics (species richness and reptile abundance) were related to fire history, vegetation structure, and habitat types, using generalized additive models. These metrics correlated with habitat-structure variables but not with fire history. The number of species increased with more complex habitats but decreased with pine-plantation abundance in the 1000-m buffer. We found contrasting responses among reptiles in terms of time since fire and those responses differed according to vegetation variables and habitat types. An unplanned fire in August 2012 provided the opportunity to compare reptile abundance values between pre-fire and the short term (1-2 years) after the fire. Most species exhibited a negative short-term response to the 2012 fire except Tarentola mauritanica, a gecko that inhabits large rocks, as opposed to other ground-dwelling species. In the reptiles studied, contrasting responses to time since fire are consistent with the habitat-accommodation model of succession. These differences are linked to specific microhabitat preferences and suggest that functional traits can be used to predict species-specific responses to fire.

Spatial variability in habitat structure and heterogenic coral reef fish assemblages inside a small-scale marine reserve after a coral mass mortality event

Coral reefs at the inner granitic islands in the Seychelles were heavily affected by the worldwide bleaching event in 1998, which led to subsequent coral mortality and widespread phase shifts to macroalgae dominated reefs. In this study, five sites within a small, but well enforced marine reserve at Cousin Island, were investigate using various methods to explore differences in coral habitat quality, coral recruitment, fish assemblages, key invertebrate grazers, and rugosity. The objective of the study was to collect a broad set of scientific data, which could be useful to describe linkage between coral reef and fish assemblages after a large-scale disturbance, as well as for future management decisions regarding marine resources, in terms of MPA protection and recovery abilities. The results showed high spatial variation in coral coverage between sites (from 1.5% to 43.2%), which were higher than previously reported, as well as high variation in dispersal of coral recruits. Furthermore, there were large heterogenic differences in fish densities and composition, which were directly linked to coral habitat quality, e.g. total fish abundance was 15 times higher on sites with high coral coverage in comparison to sites with low coral cover. In summary, this study demonstrates that coral reef habitat and fish assemblage may display high spatial variability and heterogenic differences after large-scale disturbances and suggests that potential recovery from coral mass mortality may occur in a non-linear and patchy procedure, which in turn may depend on underlying stocastical processes that affect coral recruitment and survivorship.

Stocking Rates and Vegetation Structure, Heterogeneity, and Community in a Northern Mixed-Grass Prairie

Currently, livestock management in the North American Great Plains aims for even use of forage, which creates a homogenous landscape. Reintroducing heterogeneity, defined here as the variation in vegetation structure and composition, to native North American rangelands is imperative to maintaining grassland biodiversity, and using a variety of cattle stocking rates on the landscape could accomplish this. We assessed effects of stocking rates on northern mixed-grass prairie vegetation structure, structural heterogeneity, and plant species diversity. The study took place in Grasslands National Park in Saskatchewan, Canada, using nine pastures (~300 ha) that were grazed at a range of stocking rates from very low to very high for this region. Three of these pastures were ungrazed controls. We used generalized linear mixed models to describe effects of stocking rate on vegetation over 4 years, following the reintroduction of livestock grazing to this landscape after 15 years without grazing. We used a Mantel test to determine whether plant communities changed with varying stocking rates and over time. Effects of grazing on many response variables were cumulative and changed over time. Species richness in uplands increased with stocking rate and time, but richness decreased with stocking rate in lowlands. Heterogeneity generally increased with stocking rate and time in upland but not lowland habitats. While natural annual variability influenced many variables, the cumulative effects of grazing were still apparent. A variety of stocking rates could be used to maximize structural heterogeneity and provide a diversity of habitat structure at the landscape scale.

Assessing ecological habitat structure from local to landscape scales using synthetic aperture radar

Ecological studies need accurate environmental data such as vegetation characterization, landscape structure and organization, to predict and explain the spatial distribution of biodiversity. Few ecological studies use remote sensing data to assess the biophysical or structural properties of vegetation to understand species distribution. To date, synthetic aperture radar (SAR) data have seldom been used for ecological applications. However, these sensors provide data allowing access to the inner structure of vegetation which is a key information in ecology. The objective of this article is to compare the predictive power of ecological habitat structure variables derived from a TerraSAR-X image, an aerial photograph and a SPOT-5 image for species distribution. The test was run with a hedgerow network in Brittany and assessed the spatial distribution of the forest ground carabid beetles which inhabit these hedgerows. The results confirmed that radar and optical images can be indifferently used to extract hedgerow network and derived landscape metrics (hedgerow density, network grain) useful to explain the spatial distribution of forest carabid beetles. In comparison with passive optical remotely sensed data, VHSR SAR images provide new data to characterize vegetation structure and more particularly hedgerow canopy cover, a variable known to explain the spatial distribution of carabid beetles in an agricultural landscape, but not yet quantified at a fine scale. The hedgerow canopy cover derived from the SAR image is a strong predictor of the abundance of forest carabid beetles at two scales i.e., a local scale and a landscape scale.

Using prescribed fire and herbicide to manage rank native warm season grass for northern bobwhite

Converting fields of exotic cool season grass to native warm season grass creates habitat for northern bobwhite (Colinus virginianus). If converted stands are left unmanaged they can become rank, or over-vegetated and unsuitable for grassland wildlife. Northern bobwhite populations have been declining across their range for decades, and maximizing the amount of habitat is vital to increasing their abundance. We investigated prescribed burning followed by herbicide application as a management strategy to improve vegetative composition and structure for northern bobwhite in rank native warm season grass stands. Within 4 study areas using a randomized block design, we applied the following treatments: burn-only, burn then application of 27.7% isopropylamine salt of imazapyr (ISI), burn then application of 7.78% imazapyr 62.22% diuron mixture (imazapyr), and burn then 41% glyphosate application. We measured vegetative parameters related to structure and composition and compared these metrics between treatments using repeated measures analysis of variance blocked by sampling area. We compared grass stands to hypothetical optimum conditions for bobwhite using principle components analysis. The ISI treatment produced levels of forbs and native warm season grass beneficial to bobwhite throughout the study, and was initially most similar to optimum conditions. Glyphosate treatment also produced vegetation beneficial to bobwhite. Imazapyr produced beneficial levels of bare ground during the first growing season but none of our treatments produced beneficial levels after 2 growing seasons. Herbicide treatments initially had greater influence on habitat structure than did the burn-only treatment, but all habitat structure variables were similar among treatments after 2 growing seasons. Our results indicate that management of rank grasslands for northern bobwhite occurring at <2-year intervals provides near optimal levels of native warm season grass and forbs and has potential to create habitat structure. On private lands managed for northern bobwhite where landowners do not have access to disking, we recommend prescribed burning followed by either 2.81 L/ha ISI or 5.62 L/ha glyphosate application using a non-ionic surfactant followed by annual or biennial prescribed burning. We do not recommend the use of imazapyr or burn-only treatments when managing rank grasslands for northern bobwhite habitat because they do not create beneficial levels of native warm season grass or forbs. © 2014 The Wildlife Society.

Dense understory and absence of capuchin monkeys (Sapajus xanthosternos) predict higher density of common marmosets (Callithrix jacchus) in the Brazilian Northeast.

Understanding the effects of habitat structure and other environmental variables on the density of a species can help define its habitat preferences and key ecological determinants of population parameters. The present study evaluated the effects of fragment size, the presence of a key predator/competitor, the yellow-breasted capuchin (Sapajus xanthosternos), primary productivity, the abundance of bromeliads, and habitat structure on the population density of the common marmoset (Callithrix jacchus). A total of 21 fragments were surveyed within a 350-km long zone of coastal Atlantic Forest representing the southern extreme of the distribution of the species in the Brazilian Northeast. An index of marmoset density was generated for each site based on playback surveys. The relationship between the density of marmosets and a set of parameters was evaluated by multiple regression. A Principal Components Analysis (PCA) condensed the five variables of habitat structure into two principal components, which contained 85% of their combined variation. The model that best explained the density of marmosets (R(2) = 59.1) contained the second PCA component and the presence/absence of capuchins. The analysis indicated that the marmosets prefer forests with denser understory, whether or not they are secondary habitats. The negative effect of the presence of capuchins may be related to predation pressure. The results of this study indicate that multiple-site studies may provide important insights into the habitat preferences of primate species and the factors that affect their population density.

Tadpole richness in riparian areas is determined by niche-based and neutral processes

In this study, we evaluate the effects of spatial and environmental factors on the structure of tadpole assemblages in Central Amazonia testing the following hypotheses: (1) environmental factors are more important than spatial ones in tadpole richness distribution and (2) habitat structure variables are more important than biotic variables in tadpole richness distribution. Tadpoles were sampled at 20 riparian plots between February and June 2010. Spatial and environmental components explained the major part of the variation in observed and estimated tadpole richness, respectively. Among all fitted models, the best model that explains species richness distribution is the one that contains only the number of ponds. Our results showed that tadpole richness in streamside ponds is influenced by niche-based processes and can be explained by local factors related to habitat structure. Predator density was not an important biotic factor in our study, contradicting the results found by other studies conducted in tropical areas. However, neutral processes are also important because spatial variation can explain the spatial distribution of species richness, probably as a result of dispersal limitation. Therefore, our results contribute to understanding of the local and landscape features which influence the amphibian species diversity in a tropical forest.