Figure 1.
Definition of the ecological niche used in this article.
(A) The environmental space can be represented as a set of axes (here, two: X, Y), each representing a gradient of resource or condition. A species' niche is defined as the range of each of these gradients that the species can exploit/occupy/cope with (yellow ellipse). The projection of the niche on each gradient is defined by a position (Px, Py) and a breadth (red solid lines). In our analyses, we consider two axes: (B) a thermal axis (referred to in the text as ‘thermal niche’) corresponds to a gradient of temperature; (C) a habitat axis (‘habitat niche’) refers to a gradient of vegetation structure ranging from mature forest to grasslands and open fields (see also Table 1).
Figure 2.
Map of the 1391 FBBS plots surveyed at least once during the period 2002–2008.
Each plot consists of a 4 km2 square within which the abundances of breeding birds are surveyed through 10 point counts reflecting the local diversity of habitats.
Table 1.
Description of the habitat gradient.
Figure 3.
Relationship between position and breadth in each of the niche dimensions considered (A: thermal; B: habitat) for 74 European bird species.
Thermal positions and breadths are log-transformed. Variables are scaled to mean = 0, SD = 1 for interpretability.
Figure 4.
Relationship between thermal and habitat niches for 74 European bird species.
(A) Relationship between niche positions; (B) relationship between niche breadths. The linear relationships (dashed lines) and their confidence intervals (dotted lines) are derived from averaged coefficients resulting from phylogenetic generalized least square regressions, after AICc-based model selection. Thermal positions and breadths are log transformed to approach a normal distribution. Both thermal and habitat positions are scaled to mean = 0, SD = 1. DELURB: Delichon urbicum, HIRRUS: Hirundo rustica. MOTALB: Motacilla alba. MOTFLA: Motacilla flava, PASDOM: Passer domesticus. PICPIC: Pica pica. STRDEC: Streptopelia decaocto. STRTUR: Streptopelia turtur.
Table 2.
Results of the model selection process.