Aim For the past 20 years, researchers have been challenged to demonstrate that the spatial arrangement of habitat patches actually influences the distribution of organisms and the persistence of their populations, beyond the effects of its sheer amount. More recently, it has been argued that habitat amount in the 'local landscape' surrounding a site is sufficient to predict species richness (SR) in that site, irrespective of habitat configuration. Here, we tested four predictions derived from the habitat amount hypothesis (HAH).Methods Point counts (n = 157) were conducted in five subregions to estimate forest bird SR while accounting for detectability. Surveys were conducted in mature, deciduous-dominated forest fragments, and landscape structure was quantified at three spatial scales (500, 1000 and 1500 m).Results Although we found a significant positive correlation between SR and either fragment area (FA) or habitat amount in the local landscape, predictions emphasizing the dominant influence of habitat amount and the lower influence of FA were either not supported or weakly so.Main conclusions Contrary to the HAH, we conclude that habitat amount in the local landscape is not a sufficient predictor of SR on its own. However, we agree with the contention that, in most landscape types, 'local landscapes' represent more natural spatial units than habitat fragments or 'patches'.
Knowledge of rangewide variation in abundance, and the processes driving such variation, may be the key to predict species tolerance to large-scale changes in climate and land use. Processes influencing population trends have been shown to vary between the edge and the core of a species' range. Here, we examined shifts in occurrence and abundance of a declining species, the Wood Thrush (Hylocichla mustelina), toward the northern edge of its breeding range over two to three decades. We examined those shifts at both coarse (breeding-bird atlases) and fine (individual forest fragments) spatial scales in Ontario and Québec, Canada. We hypothesized that populations would be less stable at the periphery of the range than in the core, as a result of combined effects of lower habitat quality and lower immigration rates in the periphery. At the fine spatial scale in the core of the Canadian distribution, we predicted that populations would show turnovers between years, but occurrence would remain stable at the landscape scale. As expected, Wood Thrush occurrence remained relatively stable in fragmented forests in the core of the breeding range (at both coarse and fine spatial scales), in contrast to peripheral regions. The influence of mature forest cover varied between ecoregions and spatial scales. The instability of coarse-scale occurrence patterns in peripheral versus core populations is consistent with the prediction that large-scale declines are more likely to be detected at the periphery of a species' range. However, populations declined within the core as well, albeit at a lower rate. The greater stability of core populations probably results from higher habitat quality and higher immigration rates. Yet, local recruitment within the core is expected to be low, owing to the negative effects of habitat fragmentation on productivity documented elsewhere. Perte en périphérie : les tendances dans les populations du centre des territoires par rapport aux populations périphériques d'une espèce d'oiseau chanteur migrateur en déclinRÉSUMÉ. La connaissance des variantes en termes d'abondance sur un territoire et des conditions qui déterminent ces variantes, peut être la clé pour prédire la tolérance des espèces aux changements à grande échelle du climat et de l'exploitation des terres. On a constaté que les conditions qui influencent les tendances de la population varient entre la périphérie et le centre du territoire d'une espèce. Nous avons examiné ici les évolutions de l'occurrence et de l'abondance d'une espèce en déclin, la grive des bois (Hylocichla mustelina), en direction de la bordure nord de son territoire de reproduction sur deux à trois décennies. Nous avons examiné ces évolutions sur des échelles spatiales brutes (atlas des oiseaux reproducteurs) et fines (fragments de forêts individuels) dans les provinces canadiennes de l'Ontario et du Québec. Nous avons supposé que les populations seraient moins stables à la périphérie qu'au centre de leur territoire, en conséquence des effets combinés de la baisse de la qua...
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