Gustavo A. Zurita

Species–fragmented area relationship

The species–area relationship (SAR) gives a quantitative description of the increasing number of species in a community with increasing area of habitat. In conservation, SARs have been used to predict the number of extinctions when the area of habitat is reduced. Such predictions are most needed for landscapes rather than for individual habitat fragments, but SAR-based predictions of extinctions for landscapes with highly fragmented habitat are likely to be biased because SAR assumes contiguous habitat. In reality, habitat loss is typically accompanied by habitat fragmentation. To quantify the effect of fragmentation in addition to the effect of habitat loss on the number of species, we extend the power-law SAR to the species–fragmented area relationship. This model unites the single-species metapopulation theory with the multispecies SAR for communities. We demonstrate with a realistic simulation model and with empirical data for forest-inhabiting subtropical birds that the species–fragmented area relationship gives a far superior prediction than SAR of the number of species in fragmented landscapes. The results demonstrate that for communities of species that are not well adapted to live in fragmented landscapes, the conventional SAR underestimates the number of extinctions for landscapes in which little habitat remains and it is highly fragmented.

Quantifying edge effects: the role of habitat contrast and species specialization

Edge effect is a key process influencing populations and communities, particularly in fragmented landscapes. A general analytical framework has been proposed to quantify the strength of the edge effects (extent and magnitude); however, factors determining the later remain poorly explored. Using a continuous approach we explore the response of dung beetle species and assemblages to ecotones which differ in environmental dissimilarity in the Southern Atlantic forest of Argentina. Using baited pitfall traps and automatic sensors, we estimated dung beetle abundance, microclimatic conditions and vegetation structure along five different forest-plantations transects. At the assemblages level, the majority of species showed either edge avoidance or preference; however, the response depended on the environmental dissimilarity between habitats (plantation and native forest) and varied from a neutral response on mature plantations (low contrast ecotone) to edge avoidance on recent ones (high contrast ecotone). At the species level, the degree of habitat specialization explains the differential response of species to edge effects; more specialized species showed stronger edge response while generalist species showed softer or neutral responses. Environmental dissimilarity between confronted habitats and species specialization explain the quantitative component of edge effects on species and assemblages. Functional groups (rollers and tunnellers) often showed opposite responses to edge effects. At the landscape level, functional connectivity of forest fragments is probably drastically reduced by high contrasts matrices (such as recent plantations) for native forest species, whereas soft ecotones (such as native forest-mature plantations) maintained functional connectivity. These results are particularly relevant on highly fragmented landscapes, such as the Atlantic forest, where edge effect is probably one the most important mechanisms affecting native species and communities.

Simple process-based simulators for generating spatial patterns of habitat loss and fragmentation: a review and introduction to the G-RaFFe model.

Landscape simulators are widely applied in landscape ecology for generating landscape patterns. These models can be divided into two categories: pattern-based models that generate spatial patterns irrespective of the processes that shape them, and process-based models that attempt to generate patterns based on the processes that shape them. The latter often tend toward complexity in an attempt to obtain high predictive precision, but are rarely used for generic or theoretical purposes. Here we show that a simple process-based simulator can generate a variety of spatial patterns including realistic ones, typifying landscapes fragmented by anthropogenic activities. The model “G-RaFFe” generates roads and fields to reproduce the processes in which forests are converted into arable lands. For a selected level of habitat cover, three factors dominate its outcomes: the number of roads (accessibility), maximum field size (accounting for land ownership patterns), and maximum field disconnection (which enables field to be detached from roads). We compared the performance of G-RaFFe to three other models: Simmap (neutral model), Qrule (fractal-based) and Dinamica EGO (with 4 model versions differing in complexity). A PCA-based analysis indicated G-RaFFe and Dinamica version 4 (most complex) to perform best in matching realistic spatial patterns, but an alternative analysis which considers model variability identified G-RaFFe and Qrule as performing best. We also found model performance to be affected by habitat cover and the actual land-uses, the latter reflecting on land ownership patterns. We suggest that simple process-based generators such as G-RaFFe can be used to generate spatial patterns as templates for theoretical analyses, as well as for gaining better understanding of the relation between spatial processes and patterns. We suggest caution in applying neutral or fractal-based approaches, since spatial patterns that typify anthropogenic landscapes are often non-fractal in nature.

Responses in the abundance of generalist birds to environmental gradients: The rufous-collared sparrow (Zonotrichia capensis) in the southern Neotropics

Abstract: Bird species are adapted to certain ranges of physical conditions and will respond to environmental heterogeneity depending on their ability to exploit a broad range of resources and their tolerance to new environmental conditions. We used the rufous-collared sparrow as a model to explore how the abundance of generalist passerine birds may vary along environmental gradients in the southern Neotropics. We analyzed variations in the abundance along 6 gradients expressing variations in climate, productivity, the proportion of native forest in the landscape, the proportion of vegetation types through the transition between regions, and the intensity of human activities (agriculture, urbanization). The rufous-collared sparrow was most abundant in seasonal and semi-arid climates. Thermal amplitude was the best climatic predictor of the species abundance at the large scale. Within regions where climatic conditions are relatively homogeneous, land use better predicted abundance patterns. The species responded positively to increasing primary productivity, agricultural intensity, and native forest degradation and conversion and negatively to increasing urbanization. The rufous-collared sparrow adapts successfully to new environments created by human activities such as agriculture, ranching, forestry, and urbanization. Some native species may be tolerant to certain types and intensity of human activities, and knowledge of how they respond to both natural and human-created environments may help efforts to anticipate the impact of human activities on native birds in a changing world.

Integrating Taxonomic, Functional and Phylogenetic Beta Diversities: Interactive Effects with the Biome and Land Use across Taxa

The spatial distribution of species, functional traits and phylogenetic relationships at both the regional and local scales provide complementary approaches to study patterns of biodiversity and help to untangle the mechanisms driving community assembly. Few studies have simultaneously considered the taxonomic (TBD), functional (FBD) and phylogenetic (PBD) facets of beta diversity. Here we analyze the associations between TBD, FBD, and PBD with the biome (representing different regional species pools) and land use, and investigate whether TBD, FBD and PBD were correlated. In the study design we considered two widely used indicator taxa (birds and ants) from two contrasting biomes (subtropical forest and grassland) and land uses (tree plantations and cropfields) in the southern Neotropics. Non-metric multidimensional scaling showed that taxonomic, functional and phylogenetic distances were associated to biome and land use; study sites grouped into four groups on the bi-dimensional space (cropfields in forest and grassland, and tree plantations in forest and grassland), and that was consistent across beta diversity facets and taxa. Mantel and PERMANOVA tests showed that TBD, FBD and PBD were positively correlated for both bird and ant assemblages; in general, partial correlations were also significant. Some of the functional traits considered here were conserved along phylogeny. Our results will contribute to the development of sound land use planning and beta diversity conservation.

Influence of land use on the taxonomic and functional diversity of dung beetles (Coleoptera: Scarabaeinae) in the southern Atlantic forest of Argentina.

The degradation and replacement of native ecosystems affects both their taxonomic and functional biodiversity. However, native species may find a gradient of habitat suitability in different land uses within a region. The aim of this study was to evaluate the effect of land use on the taxonomic and functional diversity of dung beetle assemblages in the southern Atlantic forest of Argentina. Dung beetles were sampled in both the native forest (control) and different land uses (Pine and Yerba mate plantations and cattle pastures) during the 2014 summer, using pitfall traps baited with human feces and rotten meat. Samplings were taken from 20 different sites, with five replicates of each land use and the native forest (100 pitfall traps in total). A total of 1699 beetles of 27 species were captured. Canthon quinquemaculatus, Canthon conformis and Dichotomius sericeus were the most abundant species. Cattle pastures were the land use most negatively affected in their taxonomic and functional diversity, particularly large paracoprid dung beetles. Pine plantations maintained their taxonomic and functional diversity in relation to the native forest and Yerba mate plantations showed, in general, an intermediate situation. Microclimatic conditions (average temperature and humidity and maximum temperature) were correlated with functional diversity (the proportion of large paracoprid dung beetles decreased with increasing temperature) and are probably good predictors to explain the observed patterns of functional diversity of dung beetles. The development of sustainable production systems that preserve the native biodiversity requires the conservation of key components from the ecological niche of native species, especially microclimatic conditions.

Influence of land use on the trophic niche overlap of dung beetles in the semideciduous Atlantic forest of Argentina

The degradation and replacement of natural ecosystems affect species abundance, diversity and interspecific interaction through the modification of resource availability and environmental conditions. Land uses preserving the forest canopy show higher species richness and similarity to the native forest. In this study, we explored changes in the trophic niche overlap of dung beetles between the native forest and different land uses in the semideciduous Atlantic forest, under the hypothesis that trophic niche overlap increases with species richness. We sampled dung beetles in protected native forests and four land uses (pine plantations, agroforestry parklands, silvo‐pastoral systems and open pastures), using seven potential food sources (monkey, feline, tapir and deer dung, decomposing fruit, decomposing fungi and carrion). The species richness of each habitat, the trophic niche overlap and the relation between both measures were analysed. Also, we explored species trophic preferences in each habitat to explain and discuss the results obtained in trophic niche overlap measures. As expected, our results showed a positive relation between species richness and trophic niche overlap. Moreover, the addition of different resources in open habitats did not increase species richness, suggesting that resource availability may not be the main mechanism explaining the empoverished dung beetle community observed in open habitats. Other mechanisms, such as physiological restrictions, may play a role in limiting the use of these habitats. Studies on the mechanisms leading to the patterns of species abundance and diversity observed in land uses are necessary to propose management recommendations that increase the sustainability of open habitats.

Expansion of the geographic range of Cyatta abscondita Sosa‑Calvo et al., 2013 (Hymenoptera: Formicidae)

The presence of the recently described fungus-farming ant genus and species Cyatta abscondita is reported in the northwestern region of Misiones Province in Argentina. A single worker of C. abscondita was collected in a pitfall trap in a mature plantation of Pinus taeda in the Atlantic Forest biome. This finding expands the distribution of the genus and species, extending it farther south in the Neotropics.

Conifer plantations in grassland and subtropical forest: Does spider diversity respond different to edge effect?

ABSTRACT Two adjacent habitats separated by an abrupt transition often cause strong alterations in environmental conditions resulting in what is called the edge effect. The structural similarity between the adjacent habitats determines how abrupt the transition is. We explored the response of spider communities to the edge effect in mature pine plantations and compared for the first time those responses in contrasting biomes (subtropical forest and grassland) in southern South America. We expect that the higher the contrast between the natural habitat and the conifer plantation, the higher will be the magnitude and the lower the extent of the response of species richness and abundance to edge effect. We sampled spiders using pitfall traps located from the edge to the plantation interior, and environmental variables were measured in pine plantations (Pinus taeda) adjacent to native grassland and subtropical forest. Results revealed that wandering spiders were sensitive to edge effect in both subtropical forest and grassland, primarily reflected by a decline in the abundance toward plantation interiors. However, the magnitude and the extent of spider abundance response to the edge effect were similar between pine plantations developing in forest and grasslands biomes. Microclimatic conditions and vegetation cover partially explained species abundance from the edge to plantation interior. Our findings suggest that conifer plantations would promote spider richness if a wide range of microhabitats were provided and support the use of spider abundance to assess edge effect in forested landscapes.

Bird Diversity in Urban Ecosystems: The Role of the Biome and Land Use Along Urbanization Gradients

Abstract Urbanization is an expanding process worldwide, causing major threats to biodiversity through both species extinction and biotic homogenization. Most studies focusing on urban ecosystems have been conducted in temperate forests of the Northern hemisphere; the ecological and socioeconomic contexts, however, may influence biodiversity responses to urbanization. We ask whether the biomes (here, the humid subtropical forest and the semiarid shrubland) where human settlements and land uses are developed determine bird diversity along urbanization gradients in the southern Neotropics. We propose theoretical responses based on expected variations in vegetation cover along urbanization gradients and fit our data to different models of bird richness from highly developed to non-urban areas and also examine changes in species composition. Species richness was positively correlated to vegetation cover in both human settlements. Results supported some of our predictions. In the city located in the arid biome, the highly developed area supported higher bird richness than the natural habitat, unlike the city from the humid biome; yet, the native bird assemblage was better preserved in the urban area established in the humid biome. Richness in moderately developed areas was either higher than or similar to that in rural or natural areas in the settlement from the arid biome, but lower than or similar to richness in the humid biome. In all the studied urban–rural gradients, bird richness reached a plateau in moderately developed areas, in contrast to urban-natural habitat gradients, where richness either increased (in the humid biome) or declined (in the arid biome). Our study helps to understand how the mechanisms changing biodiversity in urbanized areas may act in different biomes and land uses, and therefore contributes to the search of global explanations of diversity patterns.