Aveliina Helm

Extinction debt: a challenge for biodiversity conservation

Local extinction of species can occur with a substantial delay following habitat loss or degradation. Accumulating evidence suggests that such extinction debts pose a significant but often unrecognized challenge for biodiversity conservation across a wide range of taxa and ecosystems. Species with long generation times and populations near their extinction threshold are most likely to have an extinction debt. However, as long as a species that is predicted to become extinct still persists, there is time for conservation measures such as habitat restoration and landscape management. Standardized long-term monitoring, more high-quality empirical studies on different taxa and ecosystems and further development of analytical methods will help to better quantify extinction debt and protect biodiversity.

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

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.

Threatened alvar grasslands in NW Russia and their relationship to alvars in Estonia

Alvar grasslands are thin-soil calcareous grasslands on Silurian and Ordovician limestone bedrock. They are considered unique plant communities for northern Europe and America with a high conservation value. Until now, European alvar grasslands have only been described in Sweden and Estonia. We described species-rich alvar grasslands on the Izhora plateau, NW Russia and compared this vegetation with that of Estonian alvar grasslands. Floristic composition and environmental conditions of Russian alvars were similar to Estonian alvar grasslands on thicker dry soil. Russian alvars are isolated from similar communities in Estonia, but extensive transport of domestic animals from Estonia to NW Russia in past centuries has probably enhanced species dispersal. Some characteristic Estonian alvar species were missing in NW Russia because it lies outside their natural ranges. Other differences in vegetation were explained by higher atmospheric nitrogen deposition and younger age of Russian sites. In NW Russia the alvar grasslands were small, but several red-listed plant species were present. In order to preserve European alvar vegetation effectively, Russian alvar grasslands need further study and conservation as an outpost of this threatened vegetation type.

Ground-Dwelling Spider Fauna of Flooded Meadows in Matsalu, Estonia

Traditionally managed and unregulated floodplain meadows are characterised by high and habitat-specific biodiversity. In most parts of Europe, however, these habitats are almost completely lost. Despite possessing high importance in conservation, little is known about the dynamics of important species groups in those valuable communities. Here, we studied the diversity and composition of ground-dwelling spider fauna in ten sites of temporarily flooded semi-natural grasslands in the Matsalu Bay, Western Estonia. As fluctuation of aquatic and terrestrial phases is the strongest factor determining the environmental conditions in flooded coastal and floodplain meadows, we estimated the effect of floods on spider diversity and composition. Studied grasslands were characterized by opportunistic, eurytopic and hydrophilic spider species that are also abundant in other disturbed habitats. Most species belonged to families characterised by species with good dispersal ability (Linyphiidae and Lycosidae). Average ecological flexibility of spiders (i.e. number of preferred habitats) increased, while activity density of spiders declined towards the sea, where floods are more frequent and more saline. Our results indicate that the spider fauna of floodplain meadows is dependent on flooding regime and is likely re-structured after major flooding events via colonisation from nearby habitats.

Do Landscape Dissimilarity and Environmental Factors Affect Genetic and Phenotypic Variability in Myosotis laxa s. lato (Boraginaceae)

Myosotis laxa s. lato (Boraginaceae) is a morphologically highly variable taxon. We examined whether, in the Baltic Sea region, the coastal form of M. laxa has a single centre of origin or if it has emerged due to landscape dissimilarity (sea/land ratio) and environmental factors independently in different regions. We used partial Mantels test to investigate correlations between the genetic and phenotypic variability of M. laxa and the mentioned habitat factors. Although the correlation between genetic distance and the sea/land ratio existed (p < 0.01), it was not strong (r = 0.34). Phenotypic distance among populations was not correlated with habitat factors. Similarly, there was no correlation between geographic distance and morphological characteristics of the studied populations. As neither phenotypic nor genetic dissimilarity between sampled locations was correlated with geographic distance, we suggest that the coastal form can arise independently in suitable habitats and its development may be caused by epigenetic regulation. However, gene flow among the coastal and mainland populations most likely prevents stronger adaptive and genetic divergence.