Towards a more mechanistic understanding of traits and range sizes

Abstract

Aim An important, unresolved question in macroecology is to understand the immense inter‐specific variation in geographic range sizes. While species traits such as fecundity or body size are thought to affect range sizes, a general understanding on how multiple traits jointly influence them is missing. Here, we test the influence of a multitude of species traits on global range sizes of European passerine birds in order to better understand possible mechanisms behind macroecological relationships. Location Global. Methods We evaluated the effect of life‐history traits (fecundity, dispersal ability), ecological traits (habitat niche, diet niche, migratory behaviour, migratory flexibility) and a morphological trait (body size) on the global range sizes of 165 European passerines. We identified hypotheses from the literature relating traits to range size and used path analysis to test them. Results Fecundity, dispersal ability and habitat niche breadth had a direct positive effect on range size. Diet niche position had a direct negative effect on range size. Habitat niche breadth also had an indirect positive effect via higher fecundity. Migratory behaviour had an indirect positive effect via better dispersal ability. Body size had a strong positive direct effect which was reduced by negative indirect effects via several other traits. Main conclusions Geographic range sizes of European passerines were influenced by life‐history traits (fecundity and dispersal ability), ecological traits (habitat niche breadth, diet niche position and migratory behaviour) and by body size. Traits influenced range size both directly and indirectly. Body size effects were particularly complex, with positive and negative effects acting over different pathways. We show that it is necessary to disentangle the direct and indirect influence of multiple traits on range size to better elucidate the mechanisms that generate macroecological relationships.

High proportion of smaller ranged hummingbird species coincides with ecological specialization across the Americas

“…A similar positive association between modularity and TS has been documented for frugivorous bird-plant networks [49], which was argued to derive from a higher annual turnover in species composition and interactions in more seasonal environments. The combined effects of topography and climate seasonality on SRS (figure 2), together with the much stronger effect of SRS on specialization than vice versa (b ¼ 0.75 versus b ¼ 0.43), is in accordance with the hypothesis that climate stability may increase specialization through reduced annual species range dynamics [30,69], facilitating adaptation to local foraging niches. This may be caused by lower population variability in climatically stable areas, however, the direct association between niche breadth and climatically induced population dynamics still lacks sufficient support by empirical evidence [70].…”

“…Our results also have implications for conservation of species engaged in mutualistic associations, especially as anthropogenic activity may impact mutualistic interactions [74], and cause pollinator and linked plant extinctions [75,76]. For instance, the strong link between SRS and specialization indicates that some communities may be fragile in multiple ways, both by having SRS that are slow in tracking ongoing climate changes and by having specialized species less prone to switching their interactions and at higher risk of secondary extinctions [30,31,77].…”

Diet of Neotropical parrots is independent of phylogeny but correlates with body size and geographical range

“…This agrees with Laube et al . (), who found that body size, but not diet breadth, was strongly associated with geographical range in an analysis of 165 European passerines. In contrast, Slatyer et al .…”

“…, Laube et al . , but see Gaston & Blackburn ). In this case, widely distributed species simply encounter a greater variety of foods compared with species with more restricted ranges (Costa ).…”

Linking habitat specialization with species' traits in European birds

“…The effect of the area of occupancy was the strongest among all predictors and confirms that habitat specialization reflects species’ space use at large spatial scales (Gaston et al ). Because the range size is also related to several other ecological traits like diet niche, fecundity, body size or migration (Laube et al ), we controlled for its effects in all models. Therefore, the relationships between habitat specialization and other traits can be viewed as not affected by unequal range sizes of the specialist and generalist species.…”