Reproductive Inhibition of Female Peromyscus leucopus: Female Competition and Behavioral Regulation

Maturational delay of young female mice as the result of exposureto grouped female odors and reproductive inhibition as the resultof exposure to isolated adult females have both been observed(Drickamer, 1974; Skryja, 1978). Each has the potential to reducethe growth rate of populations. Reductions in a female's reproductionfacilitated by social stimulation from other females, whileeffective in reducing population growth, may in the case, ofmaturational delay and reproductive inhibition be an epiphenomenonor exadaptation of selection for improved relative reproductivesuccess in the females possessing these abilities. The ultimateoutcome of these selective processes may be the buffering ofpopulation numbers, but the selective forces may operate tomaximize a female's relative reproductive success. A females'relative reproductive success can be maximized by either increasingher own reproduction or decreasing the reproductive output ofother females. A body of evidence exists to suggest that inPeromyscus mamculatus and Peromyscus leucopus, females are physiologicallyconstrained and unable to increase their own reproduction. Ifthe assumption of physiological restraint is correct, then themost effective way for females to maximize their relative reproductivesuccess is to reduce the reproductive output of their competitors.In this paper, maturational delay and reproductive inhibitionas they affect both the adult female and young females are discussed.Examination of these effects reveals that while they can beeffective in population regulation, their main function andthe selective process that produced them is at the level ofindividual reproduction.     

Diversity of ectomycorrhizal fungi in Britain: a test of the species–area relationship, and the role of host specificity

The host range of ectomycorrhizal (ECM) fungi in Britain was examined by compilation of a data matrix from published literature sources, based primarily on accounts of sporocarp associations with particular host genera. Information was gathered for 577 species of ECM fungi belonging to 51 genera, and 25 genera of host trees, representing the majority of ECM fungal species and host genera recorded in Britain.
Pronounced variation was recorded in the number of ECM fungal species associated with different host genera, with over 200 species recorded with Betula , Fagus , Pinus and Quercus . There was a positive linear relationship ( r ²=0·47, P =0·007) between the number of species of ECM fungi associated with different host genera and the total area occupied by each tree genus in Britain (both values log-transformed). There was also variation in the number of species of ECM fungi which were apparently specific to particular host genera, values ranging from zero (in 15 genera) to >40 in the case of Betula and Fagus . In total, 233 fungal species appeared to be specific to a single host genus (i.e. 40% of those surveyed). Comparison of the ECM mycota associated with different host genera by PCA accounted for 17% of the total variation, with genera belonging to the Fagaceae ( Quercus , Fagus and Castanea ) tending to cluster together, indicating a degree of overlap in their ECM associates. Exotic conifer species, which displayed a lower ECM diversity than would be expected from their distributional areas, were characterized by a high degree of overlap with the ECM associates of Pinus and Betula .
These results indicate that the abundance of different genera of host trees and variation in host specificity could provide a basis for understanding patterns of diversity in ECM fungi within Britain.