Yearly weather variation and surface temperature drives the spatiotemporal dynamics of a threatened butterfly and its host plant

It remains unclear to what extent yearly weather variation and spatial variation in microclimate influences the outcome of interacting plant-animal species and whether responses differ between life stages. We collected data over several years on 46 ha on File Hajdar, Gotland, Sweden, and executed a complete mapping of larva nests (n = 776) and imago (n = 5,952) of the marsh fritillary butterfly Euphydryas aurinia and its host plant Succisa pratensis. The phenology of the butterflies and the major nectar plants visited varied among years. The duration of the adult flight period decreased with increasing ambient air temperatures. The density of butterflies, host plants, and host plant leaf size increased between years with increasing precipitation in the preceding year, and decreased with increasing average ambient air temperature in the preceding year. In 2021–2022 we deployed a unmanned aerial vehicle (UAV) with a high-resolution thermal sensor to measure spatial variation in surface temperatures in the study area. We found that survival from the egg to the larva stage increased with increasing surface temperature and host plant density. Host plants and larva nests generally occupied warmer microhabitats compared to imago butterflies. The results further suggested that the relationships linking surface temperature to the densities of imago, larva, host plants, and leaf size differed qualitatively between years. In 2017, larva nests and host plant density increased with increasing surface temperatures, and butterflies showed a non-linear response with a density peak at intermediate temperatures. As a result of the extreme drought in 2018 there was a reduction in maximum leaf size, and in the densities of plants, larvae, and butterflies. Moreover, the slopes of the relationships linking the density of larvae, butterflies, and plants to temperature shifted from linear positive to negative or curvilinear. Our findings demonstrate how yearly weather variation and heterogeneous surface temperatures can drive the spatiotemporal distribution and dynamics of butterflies and their host plants. The context specificity of the responses indicated by our results makes it challenging to project how climate change will affect the dynamics of ecological communities.

Well-managed grassland heterogeneity promotes butterfly conservation in a corridor network

Habitat degradation is a major concern in transformed landscapes, as it reduces complexity by removing species, interactions, and ultimately biodiversity. Degradation is also of concern for ecological networks (ENs) composed of an interconnected system of conservation corridors among South Africa's commercial forestry compartments. These corridors are predominantly grasslands, and used as rangeland, so managed to optimize grazing conditions. Yet, how this management approach influences biodiversity remains unknown. Here, we studied how butterfly assemblages respond to local differences in rangeland quality (low, high and reference sites), and how this effect compared to that of local environmental variables (e.g. rockiness and bare ground), meso environmental gradients (e.g. topographic position and aspect), and landscape composition (i.e. proportion of different land cover types in the surrounding matrix). We calculated species richness and composition, Shannon's diversity index (H'), and the Butterfly Conservation Index (BCIn) representing the proportion of sensitive and range-restricted butterfly species per site. Rangeland quality was considered less important for butterflies than other environmental variables, but it was also significantly confounded with other environmental variables. At the landscape scale, proportion of grassland in the landscape matrix influenced butterfly assemblage composition, while proportion of thicket had a significant positive effect on BCIn. Moreover, the effect of elevation on assemblage composition emphasizes the value of maintaining environmental gradients within these conservation corridors. At the meso spatial scale, butterfly species richness and diversity (H') declined with increased dominance by a single plant species, which usually occurs late in a normal fire cycle. This suggests a reliance by butterflies on recurring natural disturbances for long-term persistence. We recommend moderate patch burning and grazing, as well as occasional hot burns to reduce thicket in Afromontane grassland. This approach would improve local scale vegetation patterns, and increase heterogeneity across the landscape for conserving these butterflies into the future.

Exploring the links between social metabolism and biodiversity distribution across landscape gradients: A regional-scale contribution to the land-sharing versus land-sparing debate

The debate about the relative merits of the 'land-sparing' and 'land-sharing' approaches to biodiversity conservation is usually addressed at local scale. Here, however, we undertake a regional-scale approach to this issue by exploring the association between the Human Appropriation of Net Primary Production (HANPP) and biodiversity components (plants, amphibians, reptiles, birds and mammals) across a gradient of human-transformed landscapes in Catalonia, Spain. We propose an Intermediate Disturbance Complexity (IDC) model to assess how human disturbance of the photosynthetic capacity affects the landscape patterns and processes that host biodiversity. This model enables us to explore the association between social metabolism (HANPP), landscape structure (composition and spatial configuration) and biodiversity (species richness) by using Negative Binomial Regression (NBR), Exploratory Factor Analysis (EFA) and Structural Equation Modelling (SEM). The empirical association between IDC and landscape complexity and HANPP in Catalonia confirms the expected values of the intermediate disturbance hypothesis. There is some increase in biodiversity when high IDC values correspond to landscape mosaics. NBR and EFA show positive associations between species richness and increasing values of IDC and forest cover for all biodiversity groups except birds. SEM shows that total biodiversity is positively determined by forest cover and, to a lesser extent, by HANPP, and that both factors are negatively associated with each other. The results suggest that 'natural' landscapes (i.e. those dominated by forests) and agroforestry mosaics (i.e. heterogeneous landscapes characterized by a set of land uses possessing contrasting disturbances) provide a synergetic contribution to biodiversity conservation. This 'virtuous triangle' consisting of forest cover, HANPP and biodiversity illustrates the complex human-nature relationships that exist across landscape gradients of human transformation. This energy-landscape integrated analysis provides a robust assessment of the ecological impact of land-use policies at regional scale.

Enhancing the area-isolation paradigm: habitat heterogeneity and metapopulation dynamics of a rare wetland mammal

Conservation of species in fragmented landscapes often is guided by spatially realistic metapopulation theory. However, convincing cases of metapopulation dynamics are uncommon, especially for vertebrates. Moreover, there is concern that the patch area and isolation paradigm for metapopulations is an oversimplification for heterogeneous landscapes. We tested predictions from metapopulation theory for a rare wetland mammal (round-tailed muskrat, Neofiber alleni) and asked whether it was necessary to use a habitat-informed version of the area-isolation paradigm that included patch quality and matrix heterogeneity. In each of two years, we surveyed 457 isolated wetlands in central Florida, USA, for presence-absence of Neofiber and evaluated logistic regression models of patch occupancy, extinction, and colonization. We documented metapopulation dynamics in which patch occupancy was constant between years (26% of patches occupied) due to balanced local extinctions (n = 45) and recolonizations (n = 46). Neofiber was both habitat and dispersal limited. Local extinctions were related negatively to patch area, patch quality (cover of maidencane grass, Panicum hemitomon), and distance to nearest roadside ditch. Patch colonization depended on patch area, patch quality, and spatial connectivity to potential source wetlands. Despite the importance of patch quality, Neofiber did not exhibit a habitat-tracking metapopulation on an annual time scale. Cost-distance modeling suggested effective distances that included high costs for moving through forested matrix habitats generally were better than Euclidean distances for predicting patch colonization and occupancy. Two dominant land uses were tied to turnover dynamics: cattle grazing decreased habitat quality of wetlands, and presence of pine (Pinus spp.) plantations decreased functional connectivity. The simple area-isolation paradigm was not adequate for characterizing spatial dynamics of the Neofiber metapopulation. Nevertheless, we contend that the metapopulation approach remains a useful conservation framework for many species if landscape heterogeneity is embraced and explicit effects of land-use practices on turnover processes are considered.

Transferability of species distribution models: a functional habitat approach for two regionally threatened butterflies

Numerous models for predicting species distribution have been developed for conservation purposes. Most of them make use of environmental data (e.g., climate, topography, land use) at a coarse grid resolution (often kilometres). Such approaches are useful for conservation policy issues including reserve-network selection. The efficiency of predictive models for species distribution is usually tested on the area for which they were developed. Although highly interesting from the point of view of conservation efficiency, transferability of such models to independent areas is still under debate. We tested the transferability of habitat-based predictive distribution models for two regionally threatened butterflies, the green hairstreak (Callophrys rubi) and the grayling (Hipparchia semele), within and among three nature reserves in northeastern Belgium. We built predictive models based on spatially detailed maps of area-wide distribution and density of ecological resources. We used resources directly related to ecological functions (host plants, nectar sources, shelter, microclimate) rather than environmental surrogate variables. We obtained models that performed well with few resource variables. All models were transferable--although to different degrees--among the independent areas within the same broad geographical region. We argue that habitat models based on essential functional resources could transfer better in space than models that use indirect environmental variables. Because functional variables can easily be interpreted and even be directly affected by terrain managers, these models can be useful tools to guide species-adapted reserve management.

Making conservation decisions under uncertainty for the persistence of multiple species

Population models for multiple species provide one of the few means of assessing the impact of alternative management options on the persistence of biodiversity, but they are inevitably uncertain. Is it possible to use population models in multiple-species conservation planning given the associated uncertainties? We use information-gap decision theory to explore the impact of parameter uncertainty on the conservation decision when planning for the persistence of multiple species. An information-gap approach seeks robust outcomes that are most immune from error. We assess the impact of uncertainty in key model parameters for three species, whose extinction risks under four alternative management scenarios are estimated using a metapopulation model. Three methods are described for making conservation decisions across the species, taking into account uncertainty. We find that decisions based on single species are relatively robust to uncertainty in parameters, although the estimates of extinction risk increase rapidly with uncertainty. When identifying the best conservation decision for the persistence of all species, the methods that rely on the rankings of the management options by each species result in decisions that are similarly robust to uncertainty. Methods that depend on absolute values of extinction risk are sensitive to uncertainty, as small changes in extinction risk can alter the ranking of the alternative scenarios. We discover that it is possible to make robust conservation decisions even when the uncertainties of the multiple-species problem appear overwhelming. However, the decision most robust to uncertainty is likely to differ from the best decision when uncertainty is ignored, illustrating the importance of incorporating uncertainty into the decision-making process.