Micro-moth communities mirror environmental stress gradients within a Mediterranean nature reserve

Mediterranean moth diversity is sensitive to increasing temperatures and drought under climate change

Climate change affects ecosystems worldwide and is threatening biodiversity. Insects, as ectotherm organisms, are strongly dependent on the thermal environment. Yet, little is known about the effects of summer heat and drought on insect diversity. In the Mediterranean climate zone, a region strongly affected by climate change, hot summers might have severe effects on insect communities. Especially the larval stage might be sensitive to thermal variation, as larvae—compared to other life stages—cannot avoid hot temperatures and drought by dormancy. Here we ask, whether inter-annual fluctuations in Mediterranean moth diversity can be explained by temperature (T_Larv) and precipitation during larval development (H_Larv). To address our question, we analyzed moth communities of a Mediterranean coastal forest during the last 20 years. For species with summer-developing larvae, species richness was significantly negatively correlated with T_Larv, while the community composition was affected by both, T_Larv and H_Larv. Therefore, summer-developing larvae seem particularly sensitive to climate change, as hot summers might exceed the larval temperature optima and drought reduces food plant quality. Increasing frequency and severity of temperature and drought extremes due to climate change, therefore, might amplify insect decline in the future.

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

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.

From forest to fragment: compositional differences inside coastal forest moth assemblages and their environmental correlates

Patterns of β-diversity can provide insight into forces shaping community assembly. We analyzed species-rich insect assemblages in two reserve fragments that had once been part of one contiguous Mediterranean coastal pine forest. Local environments are still similar across both fragments, but their landscape context differs strongly, with one surrounded by intense agricultural land, while the other neighbors the urbanized area of Ravenna. Using 23,870 light-trap records of 392 moth species, and multiple local and landscape metrics, we compared the relative importance of habitat- versus landscape-scale environmental factors for shaping small-scale variation in differentiation and proportional insect β-diversity across 30 sites per reserve. Moth assemblage composition differed substantially between fragments, most likely due to ecological drift and landscape-scale variation. For proportional β-diversity, especially local forest structure was important. At well-developed forest sites, additive homogenization could be observed, whereas the lack of typical forest species at dry, dense, and younger forest sites increased species turnover (subtractive heterogenization). For differentiation β-diversity, local and landscape-scale factors were equally important in both reserves. At the landscape-scale (500 m radius around light-trapping sites) the proximity to urban areas and the fraction of human-altered land were most important. At the habitat scale, gradients in soil humidity, nutrient levels and forest structure mattered most, whereas plant diversity had very little explanatory power. Overall, landscape-scale anthropogenic alterations had major effects on moth communities inside the two conservation areas. Yet, even for these parts of one formerly contiguous forest trajectories in community change were remarkably idiosyncratic.

Multi-decadal surveys in a Mediterranean forest reserve – do succession and isolation drive moth species richness?

Isolated fragments of semi-natural habitats are often embedded in a landscape matrix that is hostile to organisms of conservation concern. Such habitat islands are prone to changes in their biota over time. For insects, few studies on long-term trends in species richness within conservation areas are available, mainly due to the lack of historical data. We here use moths in the coastal pine wood reserve Pineta san Vitale (Ravenna, NE Italy) to assess how local fauna has changed over the last 85 years. This reserve has experienced massive changes in vegetation structure due to secondary succession. We compared historical collections (1933–1976: 107 species; and 1977–1996: 157 species) with our own samples (1997–2002: 174 species; and 2011+2012: 187 species). Over the last 85 years, the proportion of habitat generalists in relation to all recorded moth species increased from 20 to 33%. The fractions of woodland and open habitat species concomitantly decreased by 10 percentage points, respectively. Amongst woodland and habitat generalist species, gains outnumbered losses. In contrast, 18 species of open habitats and 10 reed species were lost over the decades. We attribute these changes to vegetation succession and to the isolation of the reserve. Generalist species are presumably better able to pass through anthropogenically exploited landscapes and colonise isolated habitat fragments than habitat specialists.