Riinu Rannap

CONSEQUENCES OF COASTAL MEADOW DEGRADATION: THE CASE OF THE NATTERJACK TOAD (BUFO CALAMITA) IN ESTONIA

Baltic coastal meadows are among the most threatened habitats in Europe, with most residual habitat being in Estonia and Sweden. We quantitatively related the changes in this habitat type in Estonia to the history of a key inhabitant — the natterjack toad (Bufo calamita Laur.). Between the 1930s and 2000s, 67% of 52 local populations of the toad disappeared; in coastal meadows, the decline was 91%. Since the 1980s, coastal grasslands have lost their value as the main habitat for the species, and occupation of secondary habitats has not balanced the disappearance of primary habitat. According to aerial photographs from 1950–51, 1970–71, and 1996–2000, 60%–83% of the coastal meadow habitats in Estonia were lost by 2000, and the toad became extinct in more than 80% of its historical habitat. The survival of local populations was related to the sizes of managed meadows and sandy areas — larger initial areas were related to better survival, probably due to larger population size. Extinction rates exceeded habitat loss rates during advanced stages of habitat loss after 1970, probably due to the additive effects of habitat fragmentation and the disappearance of critical habitat components. Hence, habitat restoration for natterjack toads should focus on large meadow areas, and should be initiated prior to advance habitat loss. Currently, however, meadow populations of the toad in Estonia are unlikely to persist without artificial re-establishment of populations.

Northern natterjack toads (Bufo calamita) select breeding habitats that promote rapid development

It is generally believed that harsh climate inhibits growth and development of ectotherms at high latitudes. However, this environmental effect may be counterbalanced by countergradient genetic variation and habitat selection. While there is laboratory evidence for genetically based increases in growth and development rates in amphibians living at high latitudes, it remains unclear how environmental and genetic effects combine in the field to produce gradients of phenotypic variation. We performed a field study on the growth and development of tadpoles and habitat selection of breeding adults of the natterjack toad (Bufo calamita) in Denmark and in Estonia where the average onset of breeding differs by 12 days. Although growth and development of Estonian tadpoles trailed Danish conspecifics during the first half of the larval period, Estonian tadpoles caught up in both body length and developmental stage to Danish tadpoles in the last third of the larval period. Breeding ponds in Denmark were significantly larger and deeper than in Estonia, however, the water temperatures in the ponds did not vary substantially between the countries. In Estonia the toads selected shallower breeding ponds with higher temperature and oxygen concentrations, suggesting, that at higher latitudes active selection of specific water bodies ensures faster growth and development of larvae. The results, together with previous laboratory evidence, indicate that amphibian distribution limits are shaped both by adaptive differences in developmental rates and behavioural plasticity. To cope with harsh climates, amphibians in the north apparently require shallow water bodies — a habitat particularly vulnerable to anthropogenic degradation.

Macroinvertebrates in woodland pools and ditches and their response to artificial drainage in Estonia

Since the twentieth century, freshwater ecosystems have been extensively drained. Despite the magnitude of artificial drainage, its impact on freshwater biodiversity, especially on small forest waterbodies, is still poorly known. We examined macroinvertebrate taxon richness and assemblages in forest landscapes, comparing natural temporary waterbodies situated in drained and undrained areas, ditches, and wheel rut pools. We aimed to determine macroinvertebrates that are characteristic to these waterbodies, the impact of forest drainage on them, and the functioning of ditches as an alternative habitat for aquatic macroinvertebrates. Altogether 181 waterbodies within six landscape regions were surveyed, identifying 171 macroinvertebrate taxa. Taxa accumulation curves pooling all the regions indicated that natural waterbodies situated in drained areas harbored less invertebrate taxa than other waterbody types. Thus drainage has effect at supraregional scale. At the waterbody scale, however, we did not detect substantial forest drainage effect on taxon richness or assemblages. Ordering of the waterbody types by richness differed between landscape regions, suggesting that macroinvertebrates are largely dependent on landscape characteristics. Since neither total and mean richness nor assemblages did not differ significantly between natural temporary waterbodies and drainage ditches, the latter could be considered as an alternative habitat for invertebrates at least in semi-naturally managed forests.

Time-restricted flight ability influences dispersal and colonization rates in a group of freshwater beetles

Abstract Variation in the ability to fly or not is a key mechanism for differences in local species occurrences. It is increasingly acknowledged that physiological or behavioral mechanisms rather than morphological differences may drive flight abilities. However, our knowledge on the seasonal variability and stressors creating nonmorphological differences in flight abilities and how it scales to local and regional occurrences is very limited particularly for small, short‐lived species such as insects. Here, we examine how flight ability might vary across seasons and between two closely related genera of freshwater beetles with similar geographical ranges, life histories, and dispersal‐related morphology. By combining flight experiments of >1,100 specimens with colonization rates in a metacommunity of 54 ponds in northern and eastern Europe, we have analyzed the relationship between flight ability and spatio‐environmental distribution of the study genera. We find profound differences in flight ability between the two study genera across seasons. High flight ability for Acilius (97% of the tested individuals flew during the experiments) and low for Graphoderus (14%) corresponded to the different colonization rates of newly created ponds. Within a 5‐year period, 81 and 31% of the study ponds were colonized by Acilius and Graphoderus, respectively. While Acilius dispersed throughout the season, flight activity in Graphoderus was restricted to stressed situations immediately after the emergence of adults. Regional colonization ability of Acilius was independent of spatial connectivity and mass effect from propagule sources. In contrast, Graphoderus species were closely related to high connectivity between ponds in the landscape. Our data suggest that different dispersal potential can account for different local occurrences of Acilius and Graphoderus. In general, our findings provide some of the first insights into the understanding of seasonal restrictions in flight patterns of aquatic beetles and their consequences for species distributions.

Patterns of Assemblage Structure Indicate a Broader Conservation Potential of Focal Amphibians for Pond Management

Small freshwater ponds host diverse and vulnerable biotic assemblages but relatively few conspicuous, specially protected taxa. In Europe, the amphibians Triturus cristatus and Pelobates fuscus are among a few species whose populations have been successfully restored using pond restoration and management activities at the landscape scale. In this study, we explored whether the ponds constructed for those two target species have wider conservation significance, particularly for other species of conservation concern. We recorded the occurrence of amphibians and selected aquatic macro-invertebrates (dragonflies; damselflies; diving beetles; water scavenger beetles) in 66 ponds specially constructed for amphibians (up to 8 years post construction) and, for comparison, in 100 man-made ponds (created by local people for cattle or garden watering, peat excavation, etc.) and 65 natural ponds in Estonia. We analysed nestedness of the species assemblages and its dependence on the environment, and described the co-occurrence patterns between the target amphibians and other aquatic species. The assemblages in all ponds were significantly nested, but the environmental determinants of nestedness and co-occurrence of particular species differed among pond types. Constructed ponds were most species-rich irrespective of the presence of the target species; however, T. cristatus was frequent in those ponds and rare elsewhere, and it showed nested patterns in every type of pond. We thus conclude that pond construction for the protected amphibians can serve broader habitat conservation aims in the short term. However, the heterogeneity and inconsistent presence of species of conservation concern observed in other types of ponds implies that long-term perspectives on pond management require more explicit consideration of different habitat and biodiversity values. We also highlight nestedness analysis as a tool that can be used for the practical task of selecting focal species for habitat conservation.

Functional Assemblages of Macroinvertebrates in Pools and Ditches in Drained Forest Landscape

Artificially drained commercial forests are hydrologically novel ecosystems, where the array of aquatic habitats consists of ditches and remnant pools. In general the network of ditches has been found to have longer hydroperiod, the knowledge, however, about aquatic invertebrates in this system is scarce. We examined which environmental factors are impacting the biomass and abundance of functional feeding groups. Scrapers and shredders were aggregated to ditches and gatherers to pools. Filterers’ distribution pattern suggested that the function of filtering is carried out by different taxa in pools and ditches. Ditches were rather more suitable for feeding groups that rely on autochthonous resources. Acidity was a major driver of functional community composition, for example, one of the causes for higher scraper frequency in ditches. Predators exhibited greater quantities in extensive macrophyte cover regardless of water body type. Our results suggest that the trophic organization in ditches and pools is different because habitat factors select the feeding groups directly through food resources, but also because of the environmental filter on the other biological traits of the organisms. To support complex ecosystems with several trophic levels also in commercial forests, we suggest to avoid destroying macrophyte rich pools and ditches during silvicultural management.