Evol Ecol Res 4: 673-685 (2002) Full PDF if your library subscribes.
Examining Ashmole’s hypothesis: are life-history parameters of resident passerines related to the proportion of migrants?
Yoram Yom-Tov1* and Eli Geffen2
1Department of Zoology and 2Institute of Nature Conservation Research, Tel Aviv University, Tel Aviv 69978, Israel
Author to whom all correspondence should be addressed.
Ashmole’s hypothesis predicts that clutch size of birds is related to competition with migrants. This is because higher competition with migrants leads to greater winter mortality among residents, and the resultant lower competition in the breeding season enables the remaining birds to lay larger clutches. We examined the predictions of Ashmole’s hypothesis by comparing the life-history parameters of passerines inhabiting Australia, Southern Africa and India, three regions where the proportion of migrants increases in the above order. Since the proportion of migrants is higher in open habitats (grassland and semi-desert) than in closed ones (forest and rainforest), we examined the predictions of Ashmole’s hypothesis in both habitats after controlling for phylogeny. We found that body mass was positively correlated with the length of the breeding season, egg mass and the length of both incubation and fledging periods, but not with clutch size. Contrasts controlled for body mass showed that clutch size in both closed and open habitats was significantly larger in India than in both Australia and Southern Africa, as predicted by Ashmole’s hypothesis. Furthermore, the reproductive effort (clutch size multiplied by egg mass) of genera inhabiting two or all three regions showed that it was significantly larger in India than in the other two regions, thus supporting Ashmole’s hypothesis. The length of the breeding season in closed habitats was significantly different (Australia > South Africa > India) between the regions. We attribute the differences in clutch size to ecological factors, mainly the larger proportion of Palearctic migrants wintering in India. The differences in the length of the breeding season may be attributed to the different climates of the regions examined.
Keywords: Australia, breeding season, clutch size, India, passerines, Southern Africa, southern hemisphere.
DOWNLOAD A FREE, FULL PDF COPY
IF you are connected using the IP of a subscribing institution (library, laboratory, etc.)
or through its VPN.
© 2002 Yoram Yom-Tov. All EER articles are copyrighted by their authors. All authors endorse, permit and license Evolutionary Ecology Ltd. to grant its subscribing institutions/libraries the copying privileges specified below without additional consideration or payment to them or to Evolutionary Ecology, Ltd. These endorsements, in writing, are on file in the office of Evolutionary Ecology, Ltd. Consult authors for permission to use any portion of their work in derivative works, compilations or to distribute their work in any commercial manner.
Subscribing institutions/libraries may grant individuals the privilege of making a single copy of an EER article for non-commercial educational or non-commercial research purposes. Subscribing institutions/libraries may also use articles for non-commercial educational purposes by making any number of copies for course packs or course reserve collections. Subscribing institutions/libraries may also loan single copies of articles to non-commercial libraries for educational purposes.
All copies of abstracts and articles must preserve their copyright notice without modification.