Habitat fragmentation causes immediate and time‐delayed biodiversity loss at different trophic levels

Abstract

Intensification or abandonment of agricultural land use has led to a severe decline of semi-natural habitats across Europe. This can cause immediate loss of species but also time-delayed extinctions, known as the extinction debt. In a pan-European study of 147 fragmented grassland remnants, we found differences in the extinction debt of species from different trophic levels. Present-day species richness of long-lived vascular plant specialists was better explained by past than current landscape patterns, indicating an extinction debt. In contrast, short-lived butterfly specialists showed no evidence for an extinction debt at a time scale of c. 40 years. Our results indicate that management strategies maintaining the status quo of fragmented habitats are insufficient, as time-delayed extinctions and associated co-extinctions will lead to further biodiversity loss in the future.

Europe’s other debt crisis caused by the long legacy of future extinctions

“…Such extended time-lags have indeed been observed in habitat-scale studies on vascular plants (12,18) or cryptogams (25) for which historic indicators most markedly outperformed current indicators in explaining the proportion of threatened species in our countryscale study as well (Table 3). Contrary to common expectations (10,26), however, the risks faced by taxonomic groups represented by short-lived species such as dragonflies and grasshoppers seem to reflect human impacts on the environment with a delay similar to that for plants.…”

“…Recent empirical research has shown that, at the scale of individual habitat patches, a delayed response of species to habitat loss and fragmentation is indeed often detectable, particularly among habitat specialists (9)(10)(11). The likelihood and magnitude of extinction debt is still contentious, however (12,13), and seems to vary with the nature of environmental degradation and with the life history traits of the species concerned (14)(15)(16)(17)(18). In long-lived or less-mobile taxa (e.g., vascular plants, bryophytes, reptiles), a delayed response of populations to the deterioration and fragmentation of their habitats is especially likely and might extend over at least several decades.…”

“…Thus, red lists describing threatened species at either a national or global scale, which identify species extinction risks using criteria such as a reduction in population size, range size, and perceived rate of recent population or range decline (19), might be too optimistic. However, despite the recent increase in interest in the potential for temporal lags in population declines and extinction processes (8,10,12,17), evidence for extinction debt has not yet been examined for a broad range of taxa at a spatial scale consistent with national or global decision-making. Given that many conservation policies in Europe (and elsewhere) are developed and implemented at regional to global scales (e.g., Ramsar Convention and Convention on Biological Diversity) and reported at the level of individual countries, assessing extinction debt at this scale would appear to be a crucial step.…”

Testing coexistence of extinction debt and colonization credit in fragmented calcareous grasslands with complex historical dynamics

“…Anthyllis vulneraria (P=0.006), Festuca lemanii (P=0.003) and Polygala comosa (P=0.021)) were significantly less represented in "new patches". (Lindborg & Eriksson 2004;Adriaens et al 2006;Helm et al 2006;Cristofoli et al 2010a;Krauss et al 2010). Little attention has been paid to the potential contribution of secondary habitat origins through time (but see Jacquemyn et al 2003;ArroyoMora et al 2004), although it may have strong implication in metatopulation functioning (Johst et al 2002;Bossuyt & Honnay 2006).…”

“…Europe (Krauss et al 2010). The co-existence of historical fragmented and newly created patches colonized by grassland species may therefore lead to conditions of double disequilibrium regarding species richness: extinction debt and colonization credit.…”