Which plant traits predict species loss in calcareous grasslands with extinction debt?


Liina Saar, Department of Botany, Institute of Ecology and Earth Sciences, University of Tartu, Lai 40, 51005 Tartu, Estonia.
E-mail: liina.saar@ut.ee


Aim  Habitat loss and degradation pose a major threat to biodiversity, which can result in the extinction of habitat characteristic species. However, many species exhibit a delayed response to environmental changes because of the slow intrinsic dynamics of populations, resulting in extinction debt. We assess directly the changes in habitat characteristic species composition by comparing historical (1923) and current inventories in highly fragmented grasslands. We aim to characterize the species that constitute extinction debt in European calcareous grasslands.

Location  Europe, Estonia, 59–60° N, 24–25° E.

Methods  We related eleven life-history traits and selected habitat preferences to local extinctions of populations in grasslands where extinction debt has been largely paid. Traits were chosen to describe species dispersal and persistence abilities and were quantified from databases.

Results  The studied grasslands have lost 90% of their area and 30% of their characteristic plant populations in 90 years. Species more prone to local population extinction were characterized by shorter life span, self-pollination, a lack of clonal growth, fewer seeds per shoot, lower average height, lower soil nitrogen preference and higher requirements for light, indicating a limited ability to tolerate the range of changes in biotic and abiotic conditions of the sites. Locally extinct populations were also characterized by wind-dispersed seeds, lower seed weight and lower terminal velocity of seeds, suggesting that species strategies for long-distance dispersal are not favoured in highly fragmented landscapes. Thus, both increased habitat isolation and decreased habitat quality are important in determining local population extinction.

Main conclusions  Populations more prone to local extinction were characterized by a number of life-history traits, demonstrating a greater extinction risk for species with poorer abilities for local persistence and competition. Our results can be applied to less degraded grasslands where the extinction debt is not yet paid to determine those species most susceptible to future extinction.