Habitat fragmentation, tree diversity, and plant invasion interact to structure forest caterpillar communities

Abstract

Habitat fragmentation and invasive species are two of the most prominent threats to terrestrial ecosystems. Few studies have examined how these factors interact to influence the diversity of natural communities, particularly primary consumers. Here, we examined the effects of forest fragmentation and invasion of exotic honeysuckle (Lonicera maackii, Caprifoliaceae) on the abundance and diversity of the dominant forest herbivores: woody plant-feeding Lepidoptera. We systematically surveyed understory caterpillars along transects in 19 forest fragments over multiple years in southwestern Ohio and evaluated how fragment area, isolation, tree diversity, invasion by honeysuckle and interactions among these factors influence species richness, diversity and abundance. We found strong seasonal variation in caterpillar communities, which responded differently to fragmentation and invasion. Abundance and richness increased with fragment area, but these effects were mitigated by high levels of honeysuckle, tree diversity, landscape forest cover, and large recent changes in area. Honeysuckle infestation was generally associated with decreased caterpillar abundance and diversity, but these effects were strongly dependent on other fragment traits. Effects of honeysuckle on abundance were moderated when fragment area, landscape forest cover and tree diversity were high. In contrast, negative effects of honeysuckle invasion on caterpillar diversity were most pronounced in fragments with high tree diversity and large recent increases in area. Our results illustrate the complex interdependencies of habitat fragmentation, plant diversity and plant invasion in their effects on primary consumers and emphasize the need to consider these processes in concert to understand the consequences of anthropogenic habitat change for biodiversity.

Effects of Patch Size, Fragmentation, and Invasive Species on Plant and Lepidoptera Communities in Southern Texas

“…We have previously referred to the intermediate disturbance hypothesis and its suggestions that plant and Lepidoptera diversity and/or abundance could peak in disturbed habitats if they exhibit moderate levels of disturbance and thereby possess a mix of both early and late successional species [ 3 , 8 ], and/or edge and interior specialist species [ 53 ], and/or native and exotic species [ 39 , 40 ]. We cannot conclusively test or demonstrate this because, as discussed above, disturbance is so widespread that we lack a good frame of reference for undisturbed habitats in the region.…”

“…Previous studies have produced nuanced and sometimes mixed results regarding the effects of anthropogenic habitat modification on Lepidoptera communities. Most studies have found that, although some Lepidoptera species benefit, human impacts are generally detrimental to more species and to overall Lepidoptera richness, abundance, and diversity [3,23,[37][38][39][40]. However, some studies have documented positive effects of human impacts of Lepidoptera communities, for example, when introduced vegetation provides more attractive nectar sources and can cause host plant switches in butterflies [23].…”

“…However, some studies have documented positive effects of human impacts of Lepidoptera communities, for example, when introduced vegetation provides more attractive nectar sources and can cause host plant switches in butterflies [23]. Nevertheless, negative consequences of human landscape modification abound and are most often related to increased prevalence of invasive plants and declines in native plant species richness, abundance, and/or diversity, which are needed to support healthy populations of native Lepidoptera species [3,23,[37][38][39][40].…”

“…Based on prior studies, we expected higher levels of human disturbance would be associated with decreased plant community diversity or complexity, and that both of these would be associated with reduced Lepidoptera abundance and/or diversity [ 3 , 4 , 8 , 37 , 38 ]; however, intermediate levels of disturbance may demonstrate higher plant and Lepidoptera diversity and/or abundance [ 3 , 8 ]. We also expected physical attributes of habitats (patch size, edge to interior ratio) [ 52 ], structural differences (woody species prevalence) [ 8 ], and the prevalence of native versus IEP plant species to influence community composition [ 40 , 53 ].…”

State of the science and challenges of breeding landscape plants with ecological function

“…30 Separately, honeysuckle was found to cause a decrease in caterpillar abundance that was moderated when there was higher tree diversity and more intact forest cover. 31 Habitat fragmentation and homogeneity are common features of urban landscapes and they may mediate the effects of exotic plants on insect herbivores.…”