Species richness declines and biotic homogenization have slowed down for NW-European pollinators and plants

Concern about biodiversity loss has led to increased public investment in conservation. Whereas there is a widespread perception that such initiatives have been unsuccessful, there are few quantitative tests of this perception. Here, we evaluate whether rates of biodiversity change have altered in recent decades in three European countries (Great Britain, Netherlands and Belgium) for plants and flower visiting insects. We compared four 20-year periods, comparing periods of rapid land-use intensification and natural habitat loss (1930–1990) with a period of increased conservation investment (post-1990). We found that extensive species richness loss and biotic homogenisation occurred before 1990, whereas these negative trends became substantially less accentuated during recent decades, being partially reversed for certain taxa (e.g. bees in Great Britain and Netherlands). These results highlight the potential to maintain or even restore current species assemblages (which despite past extinctions are still of great conservation value), at least in regions where large-scale land-use intensification and natural habitat loss has ceased

Biodiversity at the edge: A test of the importance of spatial "mass effects" in the Rothamsted Park Grass experiments

The coexistence of many plant species competing for a few resources is one of the central puzzles of community ecology. One explanation is that different species may be competitively superior in different microhabitats. Many species could then coexist within each piece of a mosaic landscape by what has been termed "mass effects," because subpopulations in areas with negative growth rates would be supplemented by propagules from areas with reproductive surpluses. If mass effects are important, plant species diversity should increase near habitat boundaries, especially where habitat differences are moderate. In the first experimental test of this prediction, plants were censused on 54 transects within the long-established Rothamsted Park Grass plots. Very few showed significant declines in species richness with distance from subplot boundaries. Nonetheless, the regression coefficients were negative much more often than expected by chance, suggesting that weak mass effects operated. The effect was strongest where neighboring subplots differed greatly, with no evidence of the predicted decline where differences were extreme. Detailed analyses of transects with apparent mass effects revealed few species that behaved as predicted. This study serves both to provide evidence of the existence of mass effects and to question their importance in the maintenance of local plant diversity in this system

The effect of spatial resolution on projected responses to climate warming

Aim To determine how changing the resolution of modelled climate surfaces can affect estimates of the amount of thermally suitable habitat available to species under different levels of warming. Location Lake Vyrnwy RSPB Reserve, which covers around 9700 hectares of a topographically diverse landscape in Wales. Methods A recently published microclimate model was used to predict maximum, minimum and mean temperatures at 5 × 5 m resolution for the study site, under current and possible future conditions. These temperature surfaces were then averaged to produce coarser resolution surfaces, up to a maximum of 1 × 1 km resolution. Ground beetles were collected using pitfall traps between May and August 2008. Generalized linear models (GLMs) were fitted to the temperature surfaces to predict the amount of landscape suitable for a northerly-distributed ground beetle, Carabus glabratus, and the most southerly-distributed ground beetle found at the site, Poecilus versicolor, under current and possible future conditions. Results A wider range of temperatures are expected within our site when temperature is modelled at finer resolutions. Fitting GLMs at different resolutions resulted in the inclusion of different temperature variables in the best models. Coarser resolution models tended to have higher prediction error, and different resolution models predicted that different amounts of the landscape would remain or become suitable in future. There was less agreement between models for C. glabratus than for P. versicolor. Main conclusions In our example system, different resolution analyses result in different predictions about the ability of populations to survive climatic warming. Higher resolution analyses are not only likely to provide more accurate estimates of expected patterns of change, but also to highlight potential microclimatic refugia for the conservation of species that otherwise might appear to be threatened with regional or global extinction

Spatial patterns in species distributions reveal biodiversity change

Interpretation of global biodiversity change is hampered by a lack of information on the historical status of most species in most parts of the world1, 2, 3, 4, 5. Here we show that declines and increases can be deduced from current species distributions alone, using spatial patterns of occupancy combined with distribution size. Declining species show sparse, fragmented distributions for their distribution size, reflecting the extinction process; expanding species show denser, more aggregated distributions, reflecting colonization. Past distribution size changes for British butterflies were deduced successfully from current distributions, and former distributions had some power to predict future change. What is more, the relationship between distribution pattern and change in British butterflies independently predicted distribution change for butterfly species in Flanders, Belgium, and distribution change in British rare plant species is similarly related to spatial distribution pattern. This link between current distribution patterns and processes of distribution change could be used to assess relative levels of threat facing different species, even for regions and taxa lacking detailed historical and ecological information

Biodiversity change is scale-dependent: an example from Dutch and UK hoverflies (Diptera, Syrphidae)

We test whether temporal change in species richness (ΔS [%]) is scale-dependent, using data on hoverflies from the UK and the Netherlands. We analysed ΔS between pre-1980 and post-1980 periods using 5 grid resolutions (10×10, 20×20, 40×40, 80×80 and 160×160 km). We also tested the effect of data quality and of unequal survey periods on ΔS estimates, and checked for spatial autocorrelation of ΔS estimates. Using data from equal survey periods, we found significant increases in hoverfly species richness in the Netherlands at fine scales, but no significant change at coarser scales indicating a decrease in beta diversity. In the UK, ΔS was negative at fine scale, near zero at intermediate scales, and positive at coarse scales, indicating that the degree of spatial beta diversity increased between the time periods. The use of unequal survey periods (using longer periods in the past to compensate for lower survey intensity) tended to inflate past species richness, biasing ΔS estimates downwards. High data quality thresholds sometimes obscured dynamics by reducing sample size, but never reversed trends. There was little spatial autocorrelation of ΔS, implying that local drivers (land use change or environmental noise) are important in dynamics of hoverfly diversity. A second, sample agglomeration approach to measure scaling resulted in greater noise in ΔS, obscuring the NL pattern, while still showing strong evidence of fine-scale richness loss in the UK. Our results indicate that explicit considerations of spatial (and temporal) scale are essential in studies documenting past biodiversity change, or projecting change into the future

The relative importance of climate and habitat in determining the distributions of species at different spatial scales: A case study with ground beetles in Great Britain

Experimental studies have shown that many species show preferences for different climatic conditions, or may die in unsuitable conditions. Climate envelope models have been used frequently in recent years to predict the presence and absence of species at large spatial scales. However, many authors have postulated that the distributions of species at smaller spatial scales are determined by factors such as habitat availability and biotic interactions. Climatic effects are often assumed by modellers to be unimportant at fine resolutions, but few studies have actually tested this. We sampled the distributions of 20 beetle species of the family Carabidae across three study sites by pitfall trapping, and at the national scale from monitoring data. Statistical models were constructed to determine which of two sets of environmental variables (temperature or broad habitat type) best accounted for the observed data at the three sites and at the national (Great Britain) scale. High-resolution temperature variables frequently produced better models (as determined by AIC) than habitat features when modelling the distributions of species at a local scale, within the three study sites. Conversely, habitat was always a better predictor than temperature when describing species’ distributions at a coarse scale within Great Britain. Northerly species were most likely to occur in cool micro-sites within the study sites, whereas southerly species were most likely to occur in warm micro-sites. Effects of microclimate were not limited to species at the edges of their distribution, and fine-resolution temperature surfaces should therefore ideally be utilised when undertaking climate-envelope modelling