Seed germination tests of the parasitic perennial Viscum album (Viscaceae) from fragmented habitats at the northern edge of its range

Abstract

Background and aims - Despite being a rather common species throughout Europe, little is known about the effects of habitat change on the fitness of Viscum album. We expected to find a reduction in fitness in V. album populations growing in fragmented habitats resulting from a loss of genetic diversity through increased inbreeding. Methods - We studied seed germination as a measure of fitness among sixteen Belgian V. album popula tions varying in size and degree of isolation to investigate the fitness consequences of habitat fragmenta tion. Populations were sampled from two landscapes differing in their degree of habitat fragmentation and V. album population characteristics. We also compared germination percentages of three populations at three different temperatures (5, 20, 30?C) to examine the potential effects of climate change on V. album regeneration in northern Europe. Key results - Germination percentages (at 20?C) were high (69-100%) and we found no evidence of relationships between germination and population size, density, or area. There was no direct relationship between germination percentage and population isolation within study regions, but connectivity among populations appears to be important. Samples from the more fragmented habitat showed a negative correla tion between germination percentage and the proportion of females, suggesting reduced mate availability and pollination resulting from increased isolation of populations. There was no significant difference in mean germination percentages among the three temperature treatments, bui the high temperature samples (30?C) exhibited the highest variation in germination success. Conclusion - Our results suggest that V. album has evolved high germination success to compensate for limited success in establishing on a host plant. Successful germination under a wide range of environmental conditions is expected to increase the likelihood of establishing on host plants, possibly helping V. album respond to changes in climate.