Rosa Menéndez

Species richness changes lag behind climate change

Species-energy theory indicates that recent climate warming should have driven increases in species richness in cool and species-poor parts of the Northern Hemisphere. We confirm that the average species richness of British butterflies has increased since 1970–82, but much more slowly than predicted from changes of climate: on average, only one-third of the predicted increase has taken place. The resultant species assemblages are increasingly dominated by generalist species that were able to respond quickly. The time lag is confirmed by the successful introduction of many species to climatically suitable areas beyond their ranges. Our results imply that it may be decades or centuries before the species richness and composition of biological communities adjusts to the current climate.

Escape from natural enemies during climate-driven range expansion: a case study

Abstract 1. A major, and largely unexplored, uncertainty in projecting the impact of climate change on biodiversity is the consequence of altered interspecific interactions, for example between parasitoids and their hosts. The present study investigated parasitism in the Brown Argus butterfly, Aricia agestis; a species that has expanded northward in Britain during the last 30  years in association with climate warming.

DIRECT AND INDIRECT EFFECTS OF CLIMATE AND HABITAT FACTORS ON BUTTERFLY DIVERSITY

Many factors, including climate, resource availability, and habitat diversity, have been proposed as determinants of global diversity, but the links among them have rarely been studied. Using structural equation modeling (SEM), we investigated direct and indirect effects of climate variables, host-plant richness, and habitat diversity on butterfly species richness across Britain, at 20-km grid resolution. These factors were all important determinants of butterfly diversity, but their relative contributions differed between habitat generalists and specialists, and whether the effects were direct or indirect. Climate variables had strong effects on habitat generalists, whereas host-plant richness and habitat diversity contributed relatively more for habitat specialists. Considering total effects (direct and indirect together), climate variables had the strongest link to butterfly species richness for all groups of species. The results suggest that different mechanistic hypotheses to explain species richness may be more appropriate for habitat generalists and specialists, with generalists hypothesized to show direct physiological limitations and specialists additionally being constrained by trophic interactions (climate affecting host-plant richness).

METAPOPULATIONS OF FOUR LEPIDOPTERAN HERBIVORES ON A SINGLE HOST PLANT, LOTUS CORNICULATUS

Multispecies metapopulation models generally make the assumption that the interacting species occupy the same habitat network as one another. We examined the spatial distribution, metapopulation structure, and habitat network of four lepidopteran herbivores feeding on a single host plant, Lotus corniculatus, in a patchy landscape in North Wales, UK. The four species showed contrasting spatial distributions despite the fact that they feed on the same host plant. Information on dispersal rates and population turnover suggest that each species is likely to exhibit metapopulation dynamics, but with different relative contributions of local and regional processes. Detailed analyses of habitat requirements suggest that habitat networks were species-specific, and their degree of occupancy a function of the number of patches in the system. These results do not support the idea that patchiness promotes regional coexistence through multispecies metapopulation dynamics. Rather, each species appeared to act as a largely independent metapopulation system in its own specific habitat network. The results also suggest that conservation recommendations must be based on detailed analysis of the requirements of each key species in order to understand their spatial dynamics.

Migration and Allee effects in the six‐spot burnet moth Zygaena filipendulae

Abstract 1. Migration into local populations may increase the likelihood of persistence but emigration may decrease the persistence of small and isolated populations. The dispersal behaviour of a day‐flying moth Zygaena filipendulae was examined to determine whether emigration is correlated positively or negatively with population size and host plant density.

Shifts in habitat associations of dung beetles in northern Spain: Climate change implications

Abstract: We examined whether dung beetle species shift their habitat associations (vegetation types) with different climatic conditions, using altitudinal and seasonal gradients as analogues of future climate change scenarios. Dung beetle assemblages in Picos de Europa (northern Spain) were monitored by dung-baited pitfall trapping in three vegetation types (woodland, heathland, and pasture), three altitudinal zones (520-600 m, 950-963 m, and 1,230-1,275 m) and during two different seasons (summer and autumn) in 1994. Most species shifted their habitat use on the altitudinal and seasonal gradient in response to changes in microclimatic conditions (temperature). They were generally associated with heathland and woodland (shaded habitats) at lower altitudes, but they were increasingly associated with pastures (open habitat) as altitude increased. There was also a greater association with pastures in the coldest season (autumn) and with heathland and woodland in the warmest season (summer). These results suggest that climate change could be a major factor influencing habitat selection in dung beetles. The magnitude of habitat shifts was species specific, so climate warming also has the potential to generate new or different species interactions. The research presented here supports the feasibility of using microclimatic gradients within a region to study the potential effects of future climate change on both species and communities.

Measuring the success of reforestation for restoring biodiversity and ecosystem functioning

Summary 1.Effective assessment of the success of ecological restoration projects is critical in justifying the use of restoration in natural resource management as well as improving best practice. One of the main goals of ecological restoration is the recovery of ecosystem function, yet most researchers assume that increasing species and or functional diversity equates with restoration of ecosystem function, rather than empirically demonstrating these mechanistic relationships. 2.In this study we assess how dung beetle species diversity, community composition, functional diversity and ecological functions vary along a restoration chronosequence and compare restored areas with reference (rainforest) and degraded (pasture) systems. We also directly investigate the dung beetle diversity – ecosystem functioning relationship in the context of ecological rainforest restoration by testing the predictive power of traditional taxonomic indices and functional diversity metrics for functionality. 3.Species richness, abundance, biomass and functional richness all increased with restoration age, with the oldest restoration sites being most similar to rainforest; whereas functional evenness and functional divergence decreased with restoration age. Community composition in the restored areas was clearly progressing towards the rainforest sites and deviating from the pasture sites with increasing restoration age. 4.Secondary seed dispersal rates increased with restoration age, but there was only a weak positive relationship between dung removal and soil excavation and restoration age. Biodiversity metrics explained 47–74% of the variation in functions mediated by dung beetles; however, functional trait-based indices provided greater explanatory power of functionality than traditional species-based metrics. 5.Synthesis and applications. Our results provide empirical evidence on the potential of tropical forest restoration to mitigate biodiversity losses, recovering not only faunal species diversity, but also functional diversity and ecosystem functions in a relatively short period of time. We also demonstrate that functional trait-based metrics are better predictors of functionality than traditional species-based metrics but that the relationship between restoration age, diversity and ecosystem functioning is not straightforward and depends on the functions, traits and metrics used.

Can occupancy patterns be used to predict distributions in widely separated geographic regions

Occupancy models, that describe the presence and absence patterns of a species in a given area, are increasingly being used to predict the occurrence of the species in unsurveyed sites, as an aid to conservation planning. In this paper, we consider whether conclusions about local distributions derived from one landscape can be extrapolated to others. We found that habitat patchiness influenced the distribution and abundance of the host-specific moth Wheeleria spilodactylus in a similar way in two landscapes widely separated geographically. In both geographic regions, the spatial location (positive effect of connectivity), and quantity of resource (positive effect of host plant density) increased the likelihood that the moth would be present, consistent with the expectations of metapopulation dynamics. Though some biological attributes of the species appeared to be slightly different, including population density and the timing of the life cycle (phenology), occupancy patterns in one landscape accurately predict occupancy in the other landscape. Our results suggest that it maybe possible to make predictions from one landscape to another, even when the landscapes are widely separated.

Stability of butterfly assemblages in relation to the level of numerical resolution and altitude

Quick studies on biodiversity are frequently used in conservation assessments. Conclusions from these studies would be consistent if assemblages under consideration are stable over time. The stability of butterfly assemblages in the Picos de Europa in northern Spain was examined at several levels of numerical resolution. The survey was carried out in 1993 and 1995, which allowed at least one complete turnover of all individuals in each locality. Butterfly assemblages were usually stable at the levels of number of species and total number of individuals, species presence and absence, and abundance rankings. But, absolute abundances of individual species changed from 1993 to 1995 out of synchrony with one another. Regional distributions and altitudinal ranges of species were also stable. Assemblages were similar in both study years, judging by similar site ordinations by reciprocal averaging. Overall, these results are in accordance with most studies where stability has been examined at several numerical levels; they also suggest that abundances of individual species do not vary enough to disrupt overall assemblage abundance rankings. Butterfly assemblages at sites at higher altitude tended to be more unstable in terms of abundance rankings and absolute abundances. This agrees with ecological theory predicting less stable assemblages in physically ‘harsh’ environments. We concluded that monitoring for a relatively short time period can give a clear picture of both local and regional butterfly biodiversity and species composition.

Do natural enemies really make a difference? : field scale impacts of parasitoid wasps and hoverfly larvae on cereal aphid populations

Naturally occurring predators and parasitoids are known to reduce the abundance of pest invertebrates in arable crops, yet current treatment thresholds do not account for such a contribution to pest management. In the present study, we provide evidence for the presence of natural enemies correlating with a subsequent reduction in pest population growth. The abundance of cereal aphid pests and two key aphidophagous natural enemies, parasitoid wasps (Aphidiinae) and hoverfly larvae (Syrphinae), was assessed at field boundaries and interiors in southeast England. The highest rate of aphid population growth was associated with locations where no natural enemies were found. The presence of either Aphidiinae wasps or predatory Syrphinae larvae was associated with a reduction in the rate of aphid population growth, irrespective of location within the field, and overall aphid population growth was negatively correlated with increasing natural enemy abundance. The results of the present study indicate that natural enemies contribute significantly to pest control, and provide further evidence supporting the use of management strategies for promoting natural enemies in agro‐ecosystems. Aphid predators and parasitoids make an important contribution to aphid pest control within cereal fields, and thresholds for insecticide application should account for this to avoid unnecessary treatments.