Pedro Luís Bernardo da Rocha

Forest loss and the biodiversity threshold: an evaluation considering species habitat requirements and the use of matrix habitats.

Habitat loss is the main driver of the current biodiversity crisis, a landscape-scale process that affects the survival of spatially-structured populations. Although it is well-established that species responses to habitat loss can be abrupt, the existence of a biodiversity threshold is still the cause of much controversy in the literature and would require that most species respond similarly to the loss of native vegetation. Here we test the existence of a biodiversity threshold, i.e. an abrupt decline in species richness, with habitat loss. We draw on a spatially-replicated dataset on Atlantic forest small mammals, consisting of 16 sampling sites divided between forests and matrix habitats in each of five 3600-ha landscapes (varying from 5% to 45% forest cover), and on an a priori classification of species into habitat requirement categories (forest specialists, habitat generalists and open-area specialists). Forest specialists declined abruptly below 30% of forest cover, and spillover to the matrix occurred only in more forested landscapes. Generalists responded positively to landscape heterogeneity, peaking at intermediary levels of forest cover. Open area specialists dominated the matrix and did not spillover to forests. As a result of these distinct responses, we observed a biodiversity threshold for the small mammal community below 30% forest cover, and a peak in species richness just above this threshold. Our results highlight that cross habitat spillover may be asymmetrical and contingent on landscape context, occurring mainly from forests to the matrix and only in more forested landscapes. Moreover, they indicate the potential for biodiversity thresholds in human-modified landscapes, and the importance of landscape heterogeneity to biodiversity. Since forest loss affected not only the conservation value of forest patches, but also the potential for biodiversity-mediated services in anthropogenic habitats, our work indicates the importance of proactive measures to avoid human-modified landscapes to cross this threshold.

Plant species and habitat structure in a sand dune field in the brazilian Caatinga: a homogeneous habitat harbouring an endemic biota

One dune habitat in the semi-arid Caatinga Biome, rich in endemisms, is described based on plant species composition, woody plant density, mean height and phenology and a multivariate analysis of the micro-habitats generated by variables associated to plants and topography. The local flora is composed mainly by typically sand-dweller species of Caatinga, suggesting the existence of a phytogeographic unity related to the sandy areas in the Caatinga biome, which seems to be corroborated by faunal distribution. Moreover, some species are probably endemic from the dunes, a pattern also found in vertebrates. The plant distribution is patchy, there is no conspicuous herbaceous layer and almost 50% of the ground represents exposed sand. Phenology is not synchronized among species, occurring leaves budding and shedding, flowers development and anthesis, fruits production and dispersion both in rainy and dry seasons. Leaf shedding is low compared to the level usually observed in Caatinga areas and about 50% of the woody individuals were producing leaves in both seasons. Spectrum of dispersal syndromes shows an unexpected higher proportion of zoochorous species among the phanerophytes, accounting for 31.3% of the species, 78.7% of the total frequency and 78.6% of the total density. The habitat of the dunes is very simple and homogeneous in structure and most of environmental variance in the area is explained by one gradient of woody plants density and another of increase of Bromelia antiacantha Bertol. (Bromeliaceae) and Tacinga inamoena (K. Schum.) N.P. Taylor & Stuppy (Cactaceae) toward valleys, which seem to determine two kinds of protected micro-habitats for the small cursorial fauna.

Habitat structure and small mammals abundances in one semiarid landscape in the Brazilian Caatinga

Estudos realizados dentro de um grande projeto financiado pela Academia Brasileira de Ciencias na decada de 1970 concluiram que a fauna de pequenos mamiferos da regiao semiarida da Caatinga do Brasil e empobrecida e altamente restrita a afloramentos graniticos mesicos devido a falta de capacidades fisiologicas para a conservacao de agua das suas especies. Este trabalho enfoca a abundância de pequenos mamiferos em cinco habitats tipicos da Caatinga. A analise indireta de gradiente mostra que tres variaveis ambientais teoricas explicam a maior parte da variância presente na matriz de abundâncias da comunidade. A analise direta de gradiente mostra que nenhuma dessas variaveis esta altamente correlacionada a disponibilidade de afloramentos graniticos. Nossos dados tambem sugerem que a abundância na Caatinga nao e particularmente baixa quando comparada a biomas vizinhos e que os fatores subjacentes ao uso do habitat pelos pequenos mamiferos da Caatinga e mais complexo do que previamente suposto.

Electivities and resource use by an assemblage of lizards endemic to the dunes of the São Francisco River, northeastern Brazil

Este estudo descreve o padrao de uso de recursos por uma assembleia de lagartos de um campo de dunas da Caatinga. Avaliamos a disponibilidade de recursos e as fases de atividade dos lagartos, bem como seu uso e suas eletividades por alimento e micro-habitats. Seis das sete especies mais abundantes sao endemicas das dunas, e suas dietas sub-representaram artropodes com defesas quimicas. Os dois gimnoftalmideos fossorios mostraram-se semelhantes por nao apresentar eletividades por micro-habitats, mas diferiram quanto a dieta, as eletividades por alimentos e a fase de atividade. As cinco especies de lagartos epigeos incluem um grupo com eletividade positiva por micro-habitats protegidos e sombreados (Procellosaurinus erythrocercus, Briba brasiliana e Tropidurus psammonastes) e outro com eletividades negativas pelos mesmos (Eurolophosaurus divaricatus e Cnemidophorus spec. nov.). O tropidurideo T. psammonastes apresentou atividade mais precocemente pela manha, as eletividades positivas mais fortes por areas protegidas e sombreadas e eletividades negativas por areas expostas, sendo a unica especie com eletividade positiva alta por formigas. O outro tropidurideo da area, E. divaricatus, tambem alimentou-se de formigas mas apresentou eletividade positiva por flores. O teiideo de medio porte Cnemidophorus spec. nov. apresentou as maiores eletividades negativas por areas sombreadas e a maior eletividade positiva por areas abertas, bem como uma alta eletividade negativa por areas protegidas. Assim, seu padrao de uso de micro-habitat e similar ao de E. divaricatus, que possui uma dieta muito distinta, e diferente do padrao de T. psammonastes, cuja dieta e semelhante (larvas de insetos e itens de maior tamanho). Discutimos a evolucao dos padroes detectados de eletevidades por recursos.

Ecological literacy and beyond: Problem-based learning for future professionals

Ecological science contributes to solving a broad range of environmental problems. However, lack of ecological literacy in practice often limits application of this knowledge. In this paper, we highlight a critical but often overlooked demand on ecological literacy: to enable professionals of various careers to apply scientific knowledge when faced with environmental problems. Current university courses on ecology often fail to persuade students that ecological science provides important tools for environmental problem solving. We propose problem-based learning to improve the understanding of ecological science and its usefulness for real-world environmental issues that professionals in careers as diverse as engineering, public health, architecture, social sciences, or management will address. Courses should set clear learning objectives for cognitive skills they expect students to acquire. Thus, professionals in different fields will be enabled to improve environmental decision-making processes and to participate effectively in multidisciplinary work groups charged with tackling environmental issues.

What is the value of eucalyptus monocultures for the biodiversity of the Atlantic forest? A multitaxa study in southern Bahia, Brazil

Eucalyptus plantations are increasing in Brazil, frequently replacing pastures, but there is still scarce information about its capacity to maintain the fauna of neighbor forest remnants. In this study, we compared descriptors of the communities of leaf litter organisms (lizards, anurans, myriapods, arachnids, orthopterans, coleopterans, and ants) between a large remnant of primary Atlantic Forest and an adjacent eucalyptus monoculture (phase 1). Then, we compared the same descriptors for leaf litter lizards and anurans, Euglossini bees, and frugivorous butterflies among the largest remnant, small remnants at intermediate regeneration stage, and eucalyptus monocultures that were not adjacent to the largest remnant (phase 2). Monocultures were sampled immediately before logging. In phase 1, we detected significant differences in structure between the forest and the monoculture in six out of seven communities sampled. Ca. 81% of the species of the landscape were recorded in the forest, but only 54% of these were found also in the monoculture. In phase 2, the structure of two out of four forest communities was significantly different from the structure of small remnants and monocultures. On average, 76% of the species found in the whole landscape were sampled in the forest. Out of this subset, on average 74% of the species were also sampled in small remnants and 68% in monocultures. Findings of the present study point out a moderate capacity of eucalyptus monocultures to harbor species of the forest fauna even when fully grown but highlights the opportunity that they might offer for increasing connectivity in anthropogenic forest landscapes depending on their management

Habitat amount, habitat heterogeneity, and their effects on arthropod species diversity

Abstract: Not all studies have empirically supported the model that predicts a positive relationship between habitat heterogeneity and biodiversity. We hypothesized that these different results stem from the methods used to assess habitat heterogeneity; many studies used variables that are somewhat correlated in nature and measure 2 different features of the environment: a) the number of structure types (habitat heterogeneity) and b) the number of structures, disregarding their types (habitat amount). We tested this hypothesis with a single experiment that assigned orthogonal values of habitat heterogeneity and habitat amount to artificial environments located on the floor of a forest remnant. We statistically controlled the number of individuals in each environment to prevent a random sample effect. We used the number of arthropod morphospecies present in the environments after 60 d as our dependent variable. The results indicate that habitat heterogeneity had no significant effect on species richness, while habitat amount showed a positive effect when the number of individuals was not controlled. Neither habitat heterogeneity nor habitat amount affected species richness when the number of individuals was controlled. We conclude that conflicting results in previous tests of the heterogeneity model could stem from conceptual and methodological problems in experimental conception. We suggest that further studies distinguish between heterogeneity and area effects, design proper controls for different effects, and consider the spatial scale of the ecological processes that influence species diversity.

GradientLand Software: A landscape change gradient generator

Abstract In landscape ecology, there is a lack of free software that can simulate sequential processes of habitat loss using neutral landscape models. Such a tool would come to the benefit of our understanding of the effects of landscape changes on ecological processes without the need for finding or manipulating appropriate natural landscapes, something both unfeasible and sometimes unethical. This paper presents a free software, named GradientLand, as a tool for generating simulated sets of habitat loss gradients as random and fractal neutral landscapes. GradientLand is easy to handle, with an intuitive interface to create a wide array of habitat cover gradient arrangements. With this tool, we target students, teachers and researchers interested in landscape ecology and issues related to habitat loss and landscape change.

Biodiversity thresholds in invertebrate communities: The responses of dung beetle subgroups to forest loss

Extinction thresholds have been predicted to be critical values of habitat loss in which an abrupt reduction in populations occurs through the interaction between reduced habitat and increased isolation in the landscape. In communities, extinction thresholds are referred to as ‘biodiversity thresholds’. The biodiversity threshold values documented so far occur between 30% and 50% of habitat cover in landscapes. However, the assessment of biodiversity thresholds has mainly focused on vertebrate and plant communities. Here, we evaluated the occurrence of biodiversity thresholds in dung beetle communities by sampling ten 3,600 ha Atlantic Forest landscapes with forest cover ranging from 5% to 55%. We analysed the response patterns (abundance, gamma and mean alpha diversity) of community subgroups with different levels of forest dependency (forest species, generalist species, and open-area species) using model selection, comparing null, linear, bell-shaped and logistic models. The response of the community of forest species equally fits both linear and logistic models predicting a biodiversity threshold at 25% forest cover. Generalist species showed peak abundance at 20% forest cover although this result reflects a very poor generalist assembly. Open-area specialists did not respond to the amount of forest. The two most plausible models for forest species suggest two different biodiversity management options. Since the biodiversity threshold model represents a more dramatic scenario for the loss of biodiversity in Atlantic forest landscapes, we suggest, based on precautionary principle, that our results should strength guidelines that consider minimum values of forest cover in management strategies to avoid abrupt biodiversity loss and impacts on ecosystem services.

Habitat heterogeneity reduces the richness of ant species by increasing abundance of the local dominant species

The effect of environmental heterogeneity on species richness is frequently discussed in ecology. However, the empirical evidence has been contradictory as to the direction of the effect. Although some authors have considered that this might be a methodological problem, we argue that for ants, ecological interactions within the community, as interspecific competition is more important. We analyzed the plausibility of models in explaining the ant richness distribution patterns in a semi-desert environment. We used three predicting variables in the construction of the models to explain ant richness distribution: heterogeneity based on the amount of structures regardless of their type, heterogeneity based on the diversity of structures, and the abundance of individuals of the dominant species. We used ANOVA to chose the best model and corroborated the prediction that in this system abundance of dominant species is the best predictor of ant species richness. Neither of the heterogeneity conceptions contributed much to explain richness distribution. However, in a second analysis, we concluded that heterogeneity could affect the abundance of the dominant species. We conclude that competitive dominance is a better predictor of species richness distribution patterns than structural heterogeneity. However, the structural heterogeneity affects the distribution of dominant individuals. We suggest that some unexplained patterns observed about the relationship between heterogeneity and richness could be due to an indirect effect.