Qualitative and Quantitative Loss of Habitat at Different Spatial Scales Affects Functional Moth Diversity

Abstract

Land use change has led to large-scale insect decline, threatening ecosystem resilience through reduced functional diversity. Even in nature reserves, losses in insect diversity have been detected. Hereby, changes in local habitat quality and landscape-scale habitat quantity can play a role driving functional diversity toward erosion. Our aim was to analyze how local and landscape-scale factors simultaneously affect functional insect diversity. Therefore, we sampled moths in two Italian coastal forest reserves at 60 sites. Our focus was on functional richness, redundancy and niche occupation, being important for ecosystem resilience, following the insurance framework. Ecological information about 387 species and 14 traits was used to analyze functional diversity. Twenty-five functional groups were recognized and used to estimate niche occupation and redundancy. Fourteen local and 12 landscape-scale factors were measured and condensed by using Principal Components Analysis. The resulting PC-axes served as predictors in linear mixed effects models. Functional richness, redundancy and niche occupation of moths were lower at sites with low habitat quality and quantity, indicating reduced ecosystem resilience. Especially landscape diversity and habitat structure, viz. a humidity-nutrient gradient, but also plant diversity, were promoting functional richness. Landscape fragmentation, indicating increased impermeability for insects, reduced local functional richness, redundancy and niche occupation. Local habitat quality and landscape-wide habitat quantity are both important for maintaining functional insect diversity inside reserves. Therefore, small and isolated nature reserves might fail in preserving biodiversity and ecosystem functions through adverse effects acting from the surrounding landscape structure and configuration.

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

“…Our core hypothesis about human landscapes alteration was that habitat loss and fragmentation (smaller patches and higher edge to interior ratios) decrease plant community diversity and/or complexity and thereby drive decreases in Lepidoptera abundance and/or diversity. This process is broadly supported by the literature [3,4,8,37,38] and has logical bases in species area relationships [52] and spatial patterns of habitat heterogeneity [38]; however, it was only weakly supported by our observations. Patch size was a significant environmental variable in our multivariate plant community analysis, but edge to interior ratio was not (Table 4), and neither factor significantly influenced Lepidoptera or combined community compositions (Tables 5 and 6).…”

“…In addition to the relationships discussed above, higher total plant cover was correlated with higher Lepidoptera diversity, and plant richness was positively correlated with Lepidoptera encounter rates and Lepidoptera richness. All of these positive relationships have often been observed in prior studies [3,8,37,38] and may generally reflect greater resource availability and greater niche diversity for Lepidoptera arising from greater plant abundance and diversity and habitat structural complexity.…”

“…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].…”