It has been suggested that the non-random mating often observed in lekking species is a consequence of either male-male competition or active female mate choice. Here we show that the highly skewed mating distributions observed in a black grouse lek in three years were indeed different from random expectations. We suggest that females copying the mate choice of others enhance this skew. Observations in favour of copying are: females pay multiple visits to the lek during several days; females arrive and move in bands which makes it possible to observe the visits to male territories and matings of other females; in the main lek in the study area, males often mated in sequence indicating that by being visited by many females and by mating the attractiveness of males increased. However, this last effect was only evident in one of the years of the study, and only on the largest lek which had exceptionally many female visits this year. In leks with a smaller number of visiting females, copying, even if present, is difficult to detect without experiments since almost all females tend to copulate with the top-male.
The mating system of a population of individually marked common toads (Bufo bufo) was studied during two years at a pond on the island Öland, southern Sweden. The mating system can be described as explosive breeding with scramble competition for mates. Males outnumbered females by approximately 2:1 and competed for the possession of females by guarding them prior to spawning and by displacing already paired males. Data on displacement patterns showed that smaller males were displaced more often than larger males. However, successful males were not larger than the male they displaced. Furthermore, thc mean size of spawning males was not different from the population mean and the size distribution of spawning males did not differ from the size distribution expected by chance. No size assortion could be detected among spawning pairs. Female fecundity showed a strong correlation with increasing body size. Males of all sizes showed capability of fertilizing all eggs of any female. Females apparently did not choose their mates. Though males would enhance their reproductive success by mating with large and more fecund females, this scenario was probably hampered due to a short breeding season and an operational sex ratio close to 2: 1.
Two isolated rock pool localities in southern Sweden with breeding green toads (Bufo viridis) and natterjacks (B. calamita) were studied, one on the mainland coast (Vik) and one on an island in the Baltic (Utklippan). Both localities are isolated by at least 30 km from other known populations of either species. A new character, dark throat patches present in B. calamita, aided in species separation on Utklippan. Body length was larger (9-41 % ) than reported from continental Europe. Individuals intermediate between the two species in size, morphologv and mating calls were found on Utklippan, suggesting the occurrence of viable hybrids. In Vik, neither of these characters nor electrophoretic data indicated hybridization. We suggest that the number of suitable breeding ponds may explain why the two species hybridize on Utklippan since only one sympatric breeding pond could be found on this site and a number of suitable ponds were found on Vik. Thus the species may be spatially more scparated at the Vik site making hybridization less likely to occur. However, few green toad males could be found on Utklippan making the sex ratio highly skewed. Accordingly, the low number of male green toad may explain why the species hybridize. Hybridization may be a potential threat to the persistence of endangered populations already in low numbers, if a large proportion of female gametes are wasted in hybrid matings. Thus this possibility is important when considering the conservation of endangered species.