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 ecologica preve que especies generalistas de habitat sAo excluidas por especies especialistas em habitats otimos para as especialistas, e dados empiricos comumente mostram uma mudanca de dominancia das comunidades - de especialistas para generalistas - apos disturbios. Nos investigamos os padroes de coocorrencia de roedores terrestres generalistas e especialistas de habitat em duas escalas espaciais na Mata Atlantica, para testar as seguintes hipoteses: 1) a particAo espacial do nicho dento de fragmentos promove a coexistencia de generalistas e especialistas, levando a padroes de presenca-ausencia tabuleiro de damas em escalas pequenas (dentro de fragmento) mas nAo em escalas grandes (entre fragmentos); 2) a diminuicAo da abundancia de especialistas devido a perda de habitat promove uma liberacAo competitiva de generalistas, levando a covariancia negativa da abundancia de generalistas e especialistas entre fragmentos. A partir de um grande banco de dados - 363 sitios dentro de tres fragmentos de floresta continua, e 45 fragmentos dentro de tres paisagens, usamos C-scores baseados em dados de presenca/ausencia e abundancia para avaliar a segregacAo espacial. Encontramos segregacAo consistente entre especialistas e generalistas na escala menor (dentro de fragmentos) e nAo na maior (entre fragmentos), mas nAo encontramos covariancia negativa na abundancia de generalistas e especialistas entre fragmentos (dado que os pares de especies que covariaram mudou entre as paisagens). Nossos resultados sugerem que padroes espaciais causados por competicAo sAo dependentes de escala, e que a coexistencia de generalistas e especialistas e promovida pela particAo espacial de nicho dentro dos fragmentos. No entanto, a influencia da liberacAo competitiva na proliferacAo de generalistas pode ser superada por outros fatores em paisagens fragmentadas.