Contrasting Patterns of Species Richness and Functional Diversity in Bird Communities of East African Cloud Forest Fragments

Abstract

Rapid fragmentation and degradation of large undisturbed habitats constitute major threats to biodiversity. Several studies have shown that populations in small and highly isolated habitat patches are prone to strong environmental and demographic stochasticity and increased risk of extinction. Based on community assembly theory, we predict recent rapid forest fragmentation to cause a decline in species and functional guild richness of forest birds combined with a high species turnover among habitat patches, and well defined dominance structures, if competition is the major driver of community assembly. To test these predictions, we analysed species co-occurrence, nestedness, and competitive strength to infer effects of interspecific competition, habitat structure, and species′ traits on the assembly of bird species communities from 12 cloud forest fragments in southern Kenya. Our results do not point to a single ecological driver of variation in species composition. Interspecific competition does not appear to be a major driver of species segregation in small forest patches, while its relative importance appears to be higher in larger ones, which may be indicative for a generic shift from competition-dominated to colonisation-driven community structure with decreasing fragment size. Functional trait diversity was independent of fragment size after controlling for species richness. As fragmentation effects vary among feeding guilds and habitat generalists, in particular, tend to decline in low quality forest patches, we plead for taking species ecology fully into account when predicting tropical community responses to habitat change.

Environmentally and behaviourally mediated co‐occurrence of functional traits in bird communities of tropical forest fragments

“…Further, trait and environmental variable selection is partly subjective and important factors might have been ignored. However, the traits and environmental variables used here have previously been shown to influence bird community assembly (Trisos et al 2014, De Coster et al 2015 and species interactions (Ulrich et al 2016b), suggesting that they may also influence the pattern of species co-occurrence. Another shortcoming of all approaches available at present is the use of static (or snapshot) data, which potentially overlook the role of evolutionary adaptation.…”

Spatial mismatch in morphological, ecological and phylogenetic diversity, in historical and contemporary European freshwater fish faunas

“…Surprisingly, we found a very weak relation between ecological and morphological diversity concerning both richness and evenness. While several studies used morphological traits as proxies for ecological traits (Ricklefs 2012, Schleuter et al 2012, Ulrich et al 2016, its ecological meaning remains vague, and a given morphological trait can have multiple meanings (Wainwright 2007). For instance, dorsal eyed fish can either be benthic species feeding on the bottom, or surface species feeding on terrestrial insects falling on the surface (Villéger et al 2017).…”

“…species richness), functional diversity represents the variety of functional traits within the assemblage whereas the phylogenetic diversity measures its evolutionary breadth. Functional diversity encompasses a wide breadth of functional traits among which morphological and ecological traits are the most frequently considered (Ricklefs 2012, Schleuter et al 2012, Ulrich et al 2016. Nevertheless, the relationship between diversity measures based on morphological and on ecological traits remains unclear and seldom investigated.…”

Functional Diversity Metrics: How They Are Affected by Landscape Change and How They Represent Ecosystem Functioning in the Tropics

“…(3) Patch size: A positive relationship between patch size and functional richness was found for copro-necrophagous beetles [28], mammals [9], trees [32] and vertebrates [33]. Nonetheless, these results did not hold for all plant communities [11] or birds [34], in which functional richness was found to vary independently of patch size. Similarly, no effects of patch size were found on functional evenness or divergence of beetle assemblages [28].…”