Functional Roles Affect Diversity-Succession Relationships for Boreal Beetles

Heloise Gibb,Therese Johansson,Joakim Hjältén,Fredrik Stenbacka,Judi Hewitt

doi:10.1371/journal.pone.0072764

Heloise Gibb, Therese Johansson + Show 3 more

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https://doi.org/10.1371/journal.pone.0072764

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Abstract

Species diversity commonly increases with succession and this relationship is an important justification for conserving large areas of old-growth habitats. However, species with different ecological roles respond differently to succession. We examined the relationship between a range of diversity measures and time since disturbance for boreal forest beetles collected over a 285 year forest chronosequence. We compared responses of “functional” groups related to threat status, dependence on dead wood habitats, diet and the type of trap in which they were collected (indicative of the breadth of ecologies of species). We examined fits of commonly used rank-abundance models for each age class and traditional and derived diversity indices. Rank abundance distributions were closest to the Zipf-Mandelbrot distribution, suggesting little role for competition in structuring most assemblages. Diversity measures for most functional groups increased with succession, but differences in slopes were common. Evenness declined with succession; more so for red-listed species than common species. Saproxylic species increased in diversity with succession while non-saproxylic species did not. Slopes for fungivores were steeper than other diet groups, while detritivores were not strongly affected by succession. Species trapped using emergence traps (log specialists) responded more weakly to succession than those trapped using flight intercept traps (representing a broader set of ecologies). Species associated with microhabitats that accumulate with succession (fungi and dead wood) thus showed the strongest diversity responses to succession. These clear differences between functional group responses to forest succession should be considered in planning landscapes for optimum conservation value, particularly functional resilience.

Highlights

An increase in species diversity with forest age has been observed in many ecosystems [1,2,3] and is an important motivation for the conservation of significant areas of longundisturbed habitats [4]
We collected 42 457 individuals belonging to 656 species in the flight intercept traps and 9451 individuals from 279 species in the emergence traps
The exception to this was the emergence trap data, where the Zipf model was the best fit in 74% of cases

Summary

Introduction

An increase in species diversity with forest age has been observed in many ecosystems [1,2,3] and is an important motivation for the conservation of significant areas of longundisturbed habitats [4]. In regions where late successional stages previously dominated the landscape, e.g. boreal forests [8,9],, we might expect that these habitats would support more species than more recently disturbed habitats, which historically occupied a smaller area. This could result purely as a consequence of the species-area relationship [10]. Positive diversity-age relationships are common, the relationship between species diversity and succession may differ between guilds or functional groups. We expect species important in the decomposition of dead wood to be more sensitive to succession than generalised predators, which has consequences for the sustainability of those functions [5]

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Conclusion