Contrasting multi-taxa functional diversity patterns along vegetation structure gradients of woody pastures

Simon Jakobsson,Heather Wood,Regina Lindborg,Johan Ekroos

doi:10.1007/s10531-020-02037-y

Abstract

Woody pastures represent keystone habitats for biodiversity in agricultural landscapes, contributing to increased resource availability, landscape heterogeneity and structural variability. High taxonomic diversity is closely linked to vegetation structure in woody pastures, but examining functional characteristics of species assemblages can shed more light on the ecological mechanisms driving divergent responses to habitat characteristics and help guide good management practices. To this end, we use a multi-taxa approach to investigate how plant, bat and bird taxonomic and functional diversity are affected by pasture tree and shrub density, structural complexity and proximate forest cover in southern Sweden. In particular, we use a trait exclusion approach to estimate the sensitivity of diversity-environment relationships to specific traits. We found little congruence between corresponding diversity metrics across taxa. Bird species richness responded stronger to environmental variables than functional diversity metrics, whereas the functional response to the environment was stronger than the taxonomic response among plants and bats. While increasing tree densities increased the taxonomic diversity of all three taxa, a simultaneous functional response was only evident for plants. Contrasting measures of vegetation structure affected different aspects of functional diversity across taxa, driven by different traits. For plants and birds, traits linked to resource use contributed particularly to the functional response, whereas body mass had stronger influence on bat functional diversity metrics. Multi-taxa functional approaches are essential to understand the effects of woody pasture structural attributes on biodiversity, and ultimately inform management guidelines to preserve the biological values in woody pastures.

Highlights

With growing human pressure on nature, the quality of agricultural landscapes has become increasingly important for protecting biodiversity (Karp et al 2012)
We addressed the following three questions: (1) Are species richness and functional diversity metrics correlated among plants, bats and birds in woody pastures? (2) Are plant, bat and bird species richness and functional diversity metrics affected by structural vegetation attributes of woody pastures? and (3) How do specific traits and functional trait groups contribute to various functional diversity metrics, and their relations to structural vegetation attributes? We test the following hypotheses: (i) Diversity metrics generally show low congruence among the three taxa (Manning et al 2015; Birkhofer et al 2018). (ii) In contrast to species richness
Our study showed that there is little congruence between corresponding taxonomic and functional diversity metrics of plants, bats and birds in woody pastures

Summary

Introduction

With growing human pressure on nature, the quality of agricultural landscapes has become increasingly important for protecting biodiversity (Karp et al 2012). Woody pastures, consisting of a variety of grazed semi-natural grassland habitats with some tree cover (Bergmeier et al 2010), contribute significantly to landscape heterogeneity and biodiversity (Lentini et al 2012; Wood et al 2017). The trees in woody pastures are known to enhance bat species richness (Lentini et al 2012), and the mere presence of a few trees may act as keystone habitats for bats (Tews et al 2004; Fischer et al 2010). Species richness of birds in pastures tend to saturate at low to intermediate tree densities (Tellerıa 2001), shifts in bird species composition may be more strongly affected compared to species richness (Jakobsson and Lindborg 2017)

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