Smaller and Isolated Grassland Fragments Are Exposed to Stronger Seed and Insect Predation in Habitat Edges

Kitti Kuli-Révész,Péter Batáry,Tamás Lakatos,Róbert Gallé,Ágota Réka Szabó,Dávid Korányi

doi:10.3390/f12010054

Abstract

Habitat fragmentation threatens terrestrial arthropod biodiversity, and thereby also leads to alterations of ecosystem functioning and stability. Predation on insects and seeds by arthropods are two very important ecological functions because of their community-structuring effects. We addressed the effect of fragment connectivity, fragment size, and edge effect on insect and seed predation of arthropods. We studied 60 natural fragments of two grassland ecosystems in the same region (Hungarian Great Plain), 30 forest-steppes, and 30 burial mounds (kurgans). The size of fragments were in the range of 0.16–6.88 ha for forest-steppe and 0.01–0.44 ha for kurgan. We used 2400 sentinel arthropod preys (dummy caterpillars) and 4800 seeds in trays for the measurements. Attack marks on dummy caterpillars were used for predator identification and calculation of insect predation rates. In the case of seeds, predation rates were calculated as the number of missing or damaged seeds per total number of exposed seeds. Increasing connectivity played a role only in generally small kurgans, with a negative effect on insect and seed predation rates in the edges. In contrast, fragment size moderated edge effects on insect and seed predation rates in generally large forest-steppes. The difference between edges and centres was more pronounced in small than in large fragments. Our study emphasizes the important role of landscape and fragment-scale factors interacting with edge effect in shaping ecosystem functions in natural grassland fragments of modified landscapes. Managing functional landscapes to optimize the assessment of ecosystem functions and services needs a multispatial scale approach.

Highlights

Habitat loss and fragmentation are among the most relevant threats to arthropod biodiversity [1]
Increasing connectivity had a negative effect on the predation rates of edges but not in kurgan centres (Figure 2D)
We found a negative effect of connectivity on seed predation rates in edge and positive effect in centre transects (Figure 3D)

Summary

Introduction

Habitat loss and fragmentation are among the most relevant threats to arthropod biodiversity [1]. Agricultural expansion, afforestation with exotic tree species, and urbanization are the primary drivers of loss of natural or seminatural habitats and their insect communities [2], leading to small habitat fragments and decreased connectivity between them [3]. Classical island biogeography theory attempted to explain the effect of island size and distance from mainland sources on the diversity of species [4]. This concept was applied for terrestrial habitat fragments and the differences between oceanic islands, and isolated habitat fragments are well-recognized [5,6]. Habitat generalists and highly mobile species may cover large distances in a strongly modified landscape matrix [3]. The conversion of a continuous habitat into disjunct habitat fragments usually increases the length of the edges between fragments and the surrounding matrix, which may significantly change the characteristics of edges, and the plant and animal diversity of communities [10,11]

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