Habitat specialization interacts with habitat amount to determine dispersal success of rodents in fragmented landscapes

Species-habitat networks elucidate landscape effects on habitat specialisation of natural enemies and pollinators

Measuring habitat specialisation is pivotal for predicting species extinctions and for understanding consequences on ecosystem functioning. Here, we sampled pollinator and natural enemy communities in all major habitat types occurring across multiple agricultural landscapes and used species-habitat networks to determine how habitat specialisation changed along gradients in landscape composition and configuration. Although it is well known that landscape simplification often causes the replacement of specialists with generalists, our study provided evidence for intraspecific variation in habitat specialisation, highlighting how a large number of arthropod species adapted their way of selecting habitat resources depending on the landscape structure. Groups with higher diet specialisation and limited foraging flexibility appeared to have a reduced ability to respond to landscape changes, indicating that some arthropod taxa are better able than others to adapt to an increasingly broad set of resources and persist in highly impacted landscapes.

Small mammals in fragments of Atlantic Forest: species richness answering to field methods and environment

Small mammals can be used as environmental indicators and have been intensively studied in fragmented landscapes of Atlantic Forest, with a wide range of field methods. Our aim in this study was two-fold: we tested for the effects of methods and for the effects of the main environmental variables on observed small mammal richness in fragments of Atlantic Forest. We gathered information on small mammal richness, methods and environmental variables from 122 fragments of Atlantic Forest through literature review. These data were analysed using linear models and model selection based on AIC values along with a regression tree analysis. We found that studies will record more species with bigger trapping effort, using pitfall traps and sampling all forest strata. We also confirmed two important ecological assumptions: fragments at lower latitudes and bigger fragments were the ones with higher species richness. Methodological and environmental variables were analysed together on a regression tree, where trapping effort was the most important variable, surpassing any environmental effect. Considering that a significant number of the studies on Atlantic Forest fragments did not use pitfall traps or sample all forest strata, their results on forest fragmentation were affected by sampling bias.

Differential effects of habitat loss on occupancy patterns of the eastern green lizard Lacerta viridis at the core and periphery of its distribution range

The effects of habitat loss on the distribution of populations are often linked with species specialization degree. Specialist species can be more affected by changes in landscape structure and local patch characteristics compared to generalist species. Moreover, the spatial scale at which different land covers (eg. habitat, cropland, urban areas) affect specialist species can be smaller. Specialization is usually assumed as a constant trait along the distribution range of species. However, for several taxa, there is evidence of higher specialization degree in peripheral populations compared with populations in the core. Hence, peripheral populations should have a higher sensitivity to habitat loss, and strongest effects should be found at a smaller spatial scale. To test these expectations, we implemented a patch-landscape approach at different spatial scales, and compared effects of landscape structure and patch characteristics on occupancy probability among northern peripheral, more specialized populations (Czech Republic) and core populations (Bulgaria) of the eastern green lizard Lacerta viridis. We found that landscape structure and patch characteristics affect differently the occupancy probability of Lacerta viridis in each region. Strongest effects of habitat loss were found at a spatial scale of 150m around patches in the periphery, but at a scale of 500m in the core. In the periphery occupancy probability of populations was principally affected by landscape composition, and the effect of habitat quality was stronger compared to core populations. In the core, persistence of populations was mainly explained by characteristics of the spatial configuration of habitat patches. We discuss possible ecological mechanisms behind the relationship between sensitivity to habitat loss, populations' specialization degree and position in the distribution range, and suggest conservation measures for L. viridis.

The evolutionary diversity of locomotor innovation in rodents is not linked to proximal limb morphology

Rodents are the most species-rich order within Mammalia and have evolved disparate morphologies to accommodate numerous locomotor niches, providing an excellent opportunity to understand how locomotor innovation can drive speciation. To evaluate the connection between the evolutionary success of rodents and the diversity of rodent locomotor ecologies, we used a large dataset of proximal limb CT scans from across Myomorpha and Geomyoidea to examine internal and external limb shape. Only fossorial rodents displayed a major reworking of their proximal limbs in either internal or external morphology, with other locomotor modes plotting within a generalist morphospace. Fossorial rodents were also the only locomotor mode to consistently show increased rates of humerus/femur morphological evolution. We propose that these rodent clades were successful at spreading into ecological niches due to high behavioral plasticity and small body sizes, allowing them to modify their locomotor mode without requiring major changes to their proximal limb morphology.

Co-occurrence patterns of rodents at multiple spatial scales: competitive release of generalists following habitat loss?

Theory predicts that habitat generalist species are excluded by specialist species in optimal habitat for specialists, and empirical data commonly show a shift from specialist- to generalist-dominated communities following disturbance. We investigated co-occurrence patterns of habitat generalist and specialist terrestrial rodents at two spatial scales in the Atlantic Forest, aiming at evaluating the following hypotheses: 1) within-patch spatial niche partitioning promotes coexistence of generalists and specialists, leading to checkerboard presence-absence patterns at small (within-patch) rather than large (among-patch) scales; and 2) the decrease in abundance of specialists due to habitat loss promotes a competitive release of generalists, leading to negative covariance in abundance between generalists and specialists among patches. Drawing on a large data set including 363 sites within three patches in continuous forest, and 45 patches within three landscapes, we used C-scores based on presence-absence and abundance data to evaluate spatial segregation. We found consistent segregation between specialists and generalists at the within-patch rather than among-patch scale, but no consistent negative covariance in abundance between generalists and specialists among patches (as covarying species pairs varied across landscapes). Our findings suggest that spatial patterns caused by competition are scale-dependent, and coexistence of generalists and specialists is promoted by within-patch spatial niche partitioning. However, the influence of competitive release on the proliferation of generalists may be outweighed by other factors in fragmented landscapes.

A teoria ecológica prevê que espécies generalistas de habitat são excluídas por espécies especialistas em hábitats ótimos para as especialistas, e dados empíricos comumente mostram uma mudança de dominância das comunidades - de especialistas para generalistas - após distúrbios. Nós investigamos os padrões de coocorrência de roedores terrestres generalistas e especialistas de habitat em duas escalas espaciais na Mata Atlântica, para testar as seguintes hipóteses: 1) a partição espacial do nicho dento de fragmentos promove a coexistência de generalistas e especialistas, levando a padrões de presença-ausência “tabuleiro de damas” em escalas pequenas (dentro de fragmento) mas não em escalas grandes (entre fragmentos); 2) a diminuição da abundância de especialistas devido à perda de habitat promove uma liberação competitiva de generalistas, levando a covariância negativa da abundância de generalistas e especialistas entre fragmentos. A partir de um grande banco de dados - 363 sítios dentro de três fragmentos de floresta contínua, e 45 fragmentos dentro de três paisagens, usamos C-scores baseados em dados de presença/ausência e abundância para avaliar a segregação espacial. Encontramos segregação consistente entre especialistas e generalistas na escala menor (dentro de fragmentos) e não na maior (entre fragmentos), mas não encontramos covariância negativa na abundância de generalistas e especialistas entre fragmentos (dado que os pares de espécies que covariaram mudou entre as paisagens). Nossos resultados sugerem que padrões espaciais causados por competição são dependentes de escala, e que a coexistência de generalistas e especialistas é promovida pela partição espacial de nicho dentro dos fragmentos. No entanto, a influência da liberação competitiva na proliferação de generalistas pode ser superada por outros fatores em paisagens fragmentadas.

Landscape features lead to shifts in communities of medium- to large-bodied mammals in subtropical Atlantic Forest

Defaunation is a key ecological issue that has only recently been given sufficient attention. As predicted, evidence so far indicates loss of larger species followed by medium-sized species, leading to cascading effects that propagate throughout entire communities and ecosystems. The Atlantic Forest is among the most important global biodiversity hotspots. These regions have historically been impacted by habitat loss and fragmentation, resulting in landscape changes and negative impacts upon animal communities. This study evaluates community characteristics of medium- and large-sized mammals in subtropical Atlantic Forest, southern Brazil. We gathered data on mammal occurrence using 108 cameras traps located across 8 protected areas. We then tested whether landscape differences impact mammal richness, composition, and community complexity. Specifically, we used a regression tree to evaluate compositional differences as a function of landscape configuration. We analyzed data for 26 species in total, with the number of species per area ranging from 9 to 17. Changes in mammal composition at the landscape scale were most strongly associated with human occupation. Areas with strong human occupation had low species richness, with a predominance of medium-sized omnivores and insectivores species; these conditions led to high defaunation indices. Community complexity was greater in areas with low human occupation, where carnivores (Felidae) were more abundant. Differences in species composition were also linked to altitudinal bands and the ratio of period of time with protected status versus history of land exploitation in a particular area. Analysis of functional groups indicated that intense human occupation had negative effects on larger species, a process that may have impending consequences. Despite defaunation being a serious ecological issue, we assert that taking prompt action may limit or potentially reverse effects of defaunation before the most dramatic changes take place.

Defaunação é uma questão ecológica chave e que só recentemente tem recebido atenção suficiente. Como previsto, as evidências até agora indicam perda de espécies de maior porte, seguida por espécies de médio porte, levando à efeitos em cascata que se propagam em todas as comunidades e ecossistemas. A Mata Atlântica está entre os mais importantes hotspots de biodiversidade mundiais. Essa região tem sido historicamente impactada pela perda e fragmentação de hábitat, resultando em mudanças na paisagem e impactos negativos nas comunidades animais. Este estudo avalia características de comunidades de mamíferos de médio e grande porte na Mata Atlântica subtropical, sul do Brasil. Nós reunimos dados sobre ocorrência de mamíferos utilizando 108 armadilhas fotográficas instaladas em oito áreas protegidas. Em seguida, avaliamos se as diferenças de paisagem impactam a riqueza, composição e a complexidade das comunidades de mamíferos. Especificamente, nós usamos uma análise de árvore de regressão para avaliar as diferenças na composição das comunidades em função da configuração da paisagem. Analisamos ​​dados de 26 espécies no total, com o número de espécies por área variando 9 a 17. As alterações na composição de mamíferos na escala da paisagem foram mais fortemente associadas à ocupação humana. As áreas com maior ocupação humana tiveram baixa riqueza de espécies, com predominância de espécies onívoras e insetívoras de médio porte, e, estas condições geraram índices de defaunação elevados. A complexidade das comunidades foi maior em áreas com baixa ocupação humana, onde carnívoros (Felidae) foram mais frequentes. As diferenças na composição de espécies também foram ligadas às quotas de altitude, assim como à razão entre o período de tempo com estatuto de proteção e o tempo de exploração de cada área. A análise com abordagem de grupos funcionais indicou que a maior ocupação humana teve efeitos negativos sobre as espécies maiores, um processo com consequências negativas iminentes. Apesar da defaunação ser uma importante questão ecológica, nós acreditamos que um conjunto de ações conservacionistas imediatas podem potencialmente limitar ou reverter os efeitos da defaunação antes que mudanças mais dramáticas acontecem.

Assessing the utility of statistical adjustments for imperfect detection in tropical conservation science

In recent years, there has been a fast development of models that adjust for imperfect detection. These models have revolutionized the analysis of field data, and their use has repeatedly demonstrated the importance of sampling design and data quality. There are, however, several practical limitations associated with the use of detectability models which restrict their relevance to tropical conservation science.

We outline the main advantages of detectability models, before examining their limitations associated with their applicability to the analysis of tropical communities, rare species and large‐scale data sets. Finally, we discuss whether detection probability needs to be controlled before and/or after data collection.

Models that adjust for imperfect detection allow ecologists to assess data quality by estimating uncertainty and to obtain adjusted ecological estimates of populations and communities. Importantly, these models have allowed informed decisions to be made about the conservation and management of target species.

Data requirements for obtaining unadjusted estimates are substantially lower than for detectability‐adjusted estimates, which require relatively high detection/recapture probabilities and a number of repeated surveys at each location. These requirements can be difficult to meet in large‐scale environmental studies where high levels of spatial replication are needed, or in the tropics where communities are composed of many naturally rare species. However, while imperfect detection can only be adjusted statistically, covariates of detection probability can also be controlled through study design. Using three study cases where we controlled for covariates of detection probability through sampling design, we show that the variation in unadjusted ecological estimates from nearly 100 species was qualitatively the same as that obtained from adjusted estimates. Finally, we discuss that the decision as to whether one should control for covariates of detection probability through study design or statistical analyses should be dependent on study objectives.

Synthesis and applications. Models that adjust for imperfect detection are an important part of an ecologist's toolkit, but they should not be uniformly adopted in all studies. Ecologists should never let the constraints of models dictate which questions should be pursued or how the data should be analysed, and detectability models are no exception. We argue for pluralism in scientific methods, particularly where cost‐effective applied ecological science is needed to inform conservation policy at a range of different scales and in many different systems.

Models that adjust for imperfect detection are an important part of an ecologist's toolkit, but they should not be uniformly adopted in all studies. Ecologists should never let the constraints of models dictate which questions should be pursued or how the data should be analysed, and detectability models are no exception. We argue for pluralism in scientific methods, particularly where cost‐effective applied ecological science is needed to inform conservation policy at a range of different scales and in many different systems.