Site reoccupation in fragmented landscapes: testing predictions of metapopulation theory

Abstract

Summary 1.Populations of formerly continuously distributed species subdivided by habitat fragmentation may show distributions in space and time that are consistent with predictions of metapopulation theory. Local extinctions and recolonizations should result in the most fragmented sites being infrequently occupied and the least fragmented sites being continuously occupied by sensitive species. The probability of extinction is predicted to be negatively correlated with patch size and the amount of habitat in the landscape. Conversely, recolonization is predicted to be negatively correlated with the isolation of the patch, and positively correlated with the amount of habitat in the landscape. 2. Data from a 3-year study of the effect of fragmentation were used to test whether these predictions from metapopulation theory apply to populations of the long-distance migrant forest bird Piranga olivacea (Scarlet Tanager) in fragmented North American landscapes. 3. Principal components analysis was used to derive a composite measure of fragmentation. This measure was used in a logistic regression as a predictor of the number of years that territorial males would occupy a site, given that it was occupied at least once. More fragmented sites were more likely to be occupied only once; the least fragmented sites were more likely to be occupied in all three years. Data on fragmentation were necessary, but not sufficient, to predict site reoccupation, and were poor predictors at medium levels of fragmentation. 4. The univariate measures of fragmentation (patch size and isolation, proportion of forest, and forest/non-forest edge), were also used in logistic regressions to predict the separate probabilities of local extinction or recolonization. Local extinctions were negatively correlated with patch size and amount of forest in the landscape, as predicted. Recolonizations were negatively correlated with isolation of the patch as predicted, and surprisingly, also with the amount of edge in the landscape. This suggests that stochasticity may drive extinctions, but that habitat selection may play an important role in recolonization. 5. Demographic data are usually required to establish the suitability of habitat to support persistent populations, but multiple-year distributional data can provide information on habitat quality far above that obtained from single-year studies.

Landscape mosaic induces traveling waves of insect outbreaks

“…Habitat fragmentation refers to the isolation of patches of suitable habitat in a matrix of unsuitable habitat. Whether habitat fragmentation is natural or human-induced, it can have a number of significant effects on population dynamics, including lowering population densities (Andre´n 1994;Fitzgibbon 1997;Davies and Margules 1998;Didham et al 1998), increasing population densities (Cappuccino and Martin 1997;Dooley and Bowers 1998;Lecomte et al 2004), increasing population fluctuations (Fitzgibbon 1997;Lecomte et al 2004), increasing local extinction probabilities (Hames et al 2001;Lecomte et al 2004), decreasing local colonization probabilities (Hames et al 2001), reducing gene flow (Bacles et al 2004), and decreasing genetic variation (Young et al 1993). On a regional scale, metapopulation theory makes the prediction that organisms living in highly fragmented habitats are more prone to regional extinction than those in wellconnected habitats (Thomas and Harrison 1992;Hanski and Ovaskainen 2000), resulting in lower species diversity in highly fragmented habitats (Ferraz et al 2003).…”

Neighbour–stranger discrimination by Yellow-bellied Tit Parus venustulus: evidence for the “dear-enemy” effect

“…PCA analysis was conducted using SPSS for Windows release 15.0.1 (SPSS Inc. 2006). The final principal components were rotated using the Varimax method to assist interpretation of factor solutions (Hames et al 2001;Bailey et al 2002). The components were then interpreted using the component loadings (correlations between the principal component and each original variable).…”

Citizens, science and bird conservation

“…Because of concerns about the impact that management of the countryside will have on birds, it has become common for surveys to be directed at specific questions; for example, the effect of forest fragmentation on Scarlet Tanagers Piranga olivacea in eastern North America (Hames et al 2001), the value of ''set-aside'' land for farmland birds in Britain (Henderson et al 2000), and the possible benefits of organic farming (Chamberlain et al 1999b;Fuller et al 2005). The questions asked in such studies are so specific that the methods have tended to be more rigorous than those included in the general surveys, so the participants and study sites may be numbered in the dozens rather than the hundreds.…”