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

Abstract

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.

Figure 1

Change in species richness (estimated weighted mean ± 95% confidence intervals) of flower visitors and plants through time at different spatial scales. For most taxa and countries richness change estimates (% of change) of flower visitors and plants were more accentuated between P1 and P2 (the Netherlands, a, g, Belgium, c, i, and Great Britain, e, k) than between P2 and P3 (the Netherlands, b, h, Belgium, d, j, and Great Britain, f, l). Due to insufficient number of grid cells, results from some spatial scales are not presented for some groups. The horizontal line represents no change (0%). Filled symbols indicate that change was significantly different from zero, otherwise symbols are open (see statistical details in Table S2).

Figure 2

Changes in species compositional similarity (1-βsim) of plants and flower visitors among 10-km grid cells through space and time. Decline in similarity with distance is presented for bees, hoverflies, butterflies, plants dependent on insects for pollination, plants of intermediate dependence and plants independent of insects for pollination of the Netherlands (a, b, c, j, k, l, respectively), Belgium (d, e, f, m, n, o) and Great Britain (g, h, i, p, q, r). Strong patterns of spatial homogenisation (i.e. increases in similarity) were detected between P1 and P2 (a, c, e, i, j, k, l). Lines represent the estimated value of similarity ± 95% confidence intervals, after removing the effect of sampling effort (for statistical details see Table S3). Data were insufficient for butterflies in Belgium for time period P1.