Amfibieën en reptielen

Eight amphibians and one reptile species occur in the Flemish coastal dunes. None of these is characteristic for this region but the common lizard [Lacerta vivpara], great crested newt [Triturus cristatus], natterjack toad [Bufo calamita] and tree frog [Hyla arborea] deserve special attention for conservation. L. Vivipara occurs in structurally rich dune landscapes while the three amphibians need open water for their reproduction. Triturus cristatus occurs in ponds with submerged vegetation. B. Calamita reproduces in temporal ponds with unvegetated, sandy banks and young dune slacks, mainly along the western part of the coast. Hyla arborea is only found along at the inner dune ridge of the Zwin area near the Dutch border [Knokke]

Genetic and demographic vulnerability of adder populations: Results of a genetic study in mainland Britain

Genetic factors are often overlooked in conservation planning, despite their importance in small isolated populations. We used mitochondrial and microsatellite markers to investigate population genetics of the adder (Vipera berus) in southern Britain, where numbers are declining. We found no evidence for loss of heterozygosity in any of the populations studied. Genetic diversity was comparable across sites, in line with published levels for mainland Europe. However, further analysis revealed a striking level of relatedness. Genetic networks constructed from inferred first degree relationships suggested a high proportion of individuals to be related at a level equivalent to that of half-siblings, with rare inferred full-sib dyads. These patterns of relatedness can be attributed to the high philopatry and low vagility of adders, which creates high local relatedness, in combination with the polyandrous breeding system in the adder, which may offset the risk of inbreeding in closed populations. We suggest that reliance on standard genetic indicators of inbreeding and diversity may underestimate demographic and genetic factors that make adder populations vulnerable to extirpation. We stress the importance of an integrated genetic and demographic approach in the conservation of adders, and other taxa of similar ecology

Fate of the predictions in Galle-Unawatuna mangroves, Sri Lanka: A validation after 10 years using satellite (IKONOS) and ground-truth data

Validation of earlier predictions is a challenging but significant contribution to ecological research. The present study tests the predications made 10 years ago by Dahdouh-Guebas et al. (2000) on the evolution of mangrove forest in Galle-Unawatuna, Sri Lanka. The ground inventory carried out in five Sectors covering the entire forest (Point Centred Quarter Method - PCQM) (Cintron and Schaeffer Novelli, 1984) revealed that the adult species composition is dominated by Rhizophora apiculata, Excoecaria agallocha, Bruguiera gymnorrhiza and B. sexangula, with their total density of 216-267 stems 0.1ha-1 and basal area 1.19-1.44m2 0.1ha-1. However, both young and juvenile vegetation in the most Sectors was dominated solely by B. gymnorrhiza (128-869 stems and 356-1482 propagules 0.1ha-1). According to Dahdouh-Guebas et al. (2000), the transition of an E. agallocha forest into a B. gymnorrhiza dominated one or at least their co-dominance in the Sectors 1 and 2 is possible, whereas Sector 3 being dominated by adult and juvenile R. apiculata will persist. Overall, the possible transition to a Bruguiera dominated forest in Galle-Unawatuna area was forecasted. The recent decadal changes between 1994 and 2004 through the integration of IKONOS satellite imagery of 2004 with ground-truth information confirmed many of the predictions and showed dynamic shifts in young/adult vegetation by B. gymnorrhiza. Both E. agallocha and R. apiculata continue to be dominant in Sectors 2 and 3, although the adult turnover by B. gymnorrhiza has not yet occurred, probably due to the small time interval between the two investigations. Confirming in part with the earlier prediction on R. apiculata in Sector 3, present study also revealed the abundance of B. gymnorrhiza as young and juvenile vegetation. Viewing the present dynamic shifts and sheer dominance as young vegetation by B. gymnorrhiza with a mean height of 5.8m in most Sectors, it is still possible to anticipate the mangroves being dominated by this species, and actually now validates the predictions made 10 years ago. Because of apparent changes in the mangrove vegetation structure, it could be concluded that the ‘moving mosaic’ pattern of mangrove species distribution reported earlier for Galle-Unawatuna still persists