摘要:

The paper describes an investigation of parasite richness in relation to host life history and ecology using data from an extensive survey of helminth parasites (cestodes, trematodes and nematodes) in Soviet birds. Correlates of parasite richness (number of parasite species per host species) were sought among 13 life‐history variables, 13 ecological variables and one non‐biological variable (number of host individuals examined) across a sample of 158 species of host. A statistical method to control for the effects of phylogenetic association was adopted throughout. Parasite richness correlates positively with the number of hosts examined (sample size) in all three parasite groups. Positive correlations (after controlling for the effects of sample size) were also found between host body weight and parasite richness for trematodes and nematodes, but not for cestodes.A number of ecological variables were associated with parasite richness. However, when the effects of sample size and body weight were controlled for, only a single significant correlation (an association between trematode richness and aquatic habitat) remained. Similarly, a number of significant correlates of parasite richness were found among the life‐history variables examined. Though several of these were robust to the confounding effects of sample size, all could be explained by the co‐variation between life‐history traits and body weight among the host species under inve

ISSN:0024-4066    

DOI:10.1111/j.1095-8312.1991.tb00597.x

出版商:Blackwell Publishing Ltd    

年代:1991

数据来源: WILEY

摘要:

The use of the epithet ‘adaptive’ in the popular denotation ‘adaptive radiation’ suggests that radiation as such does not imply adaptation. Without trying to define radiation more sharply than is usually done in textbooks, emphasis is given to what might be called non‐adaptive radiation, a kind of diversification not accompanied by adaptation into various significantly different niches and, therefore, resulting in a group of allopatric species which are isolated because of competitive int

ISSN:0024-4066    

DOI:10.1111/j.1095-8312.1991.tb00598.x

出版商:Blackwell Publishing Ltd    

年代:1991

数据来源: WILEY

摘要:

In natural populations of the land snailCepaea hortensisthere is often a negative association between shell size and population density. The usual interpretation of such associations, both inC. hortensisand other species, is that they represent an ecophenotypic effect that is part of a system of density‐dependent natality, rather than a genetically‐based effect that is produced through density‐related selection. However, this interpretation is usually based on supposition rather than evidence. Here we present the results of an experiment in which small juveniles collected from two sampling sites within a colony known to exhibit a negative size‐density association were grown to maturity under constant laboratory conditions. The highly significant inter‐site difference observed in the wild disappeared in the laboratory‐reared snails, indicating the direct influence of environmental factors on size. Because of the nature of the data‐sets from which density‐dependent natality is inferred, this result has a clearer connection with such density dependence than conventional within‐population herit

ISSN:0024-4066    

DOI:10.1111/j.1095-8312.1991.tb00599.x

出版商:Blackwell Publishing Ltd    

年代:1991

数据来源: WILEY

摘要:

To prove that predators are morphologically adapted to the size of their prey one has to demonstrate that the morphological variation in the trophic apparatus is related to the prey size distribution and that the variation in the trait has some effect on individual fitness. I have studied geographic variation in relative head length (RHL) of adders,Vipera berus, on the Swedish mainland and on groups of islands in the Baltic Sea, and the relationship between RHL and physical condition, a character related to fitness. I also examined the relationship between RHL and sex and colour morph. Relative head length of adders was smallest on the mainland and increased on the islands with increasing body size of the main prey,Microtus agrestis, suggesting stabilizing selection for head size within each population. There was no difference in RHL between sexes or colour morphs. However, physical condition was positively correlated with RHL, indicating directional selection for larger heads. The observed pattern is interpreted as an evolutionary response to the geographic variation in body size of the main prey species and the smaller number of alternative prey species available on islands.

ISSN:0024-4066    

DOI:10.1111/j.1095-8312.1991.tb00600.x

出版商:Blackwell Publishing Ltd    

年代:1991

数据来源: WILEY

摘要:

Colonies of a social spiderAchaearanea wau(Theridiidae) from Papua, New Guinea have adult and juvenile sex ratios that are biased towards females, and this probably represents a primary bias at the egg stage. Adult sex ratios are less female‐biased than are juvenile sex ratios, and both vary significantly among colonies. Adult sex ratios covary with colony size: small colonies have a larger proportion of males than large ones. The pattern of variation in adult sex ratio may be due to greater mortality of females than of males during maturation. Juvenile sex ratios do not covary with colony size, nor do they differ among populations. Colony size, however, does have a significant effect on survival and dispersal in colonies. I conclude, therefore, that a conditional sex ratio strategy, in which the primary sex ratio of the colony is adjusted to changing demographic patterns, does not occur inA. wau.I suggest that environmental heterogeneity acting on individual reproductive output may be responsible for the observed variation among colonies in juvenile sex ratio

ISSN:0024-4066    

DOI:10.1111/j.1095-8312.1991.tb00601.x

出版商:Blackwell Publishing Ltd    

年代:1991

数据来源: WILEY

摘要:

The arrangement of sperm within the spermatheca of the impregnated rabbit flea is described. The numerical superiority of the sperm injections from the numerous later matings suggests that a modified form of sperm displacement probably occurs in this species.

ISSN:0024-4066    

DOI:10.1111/j.1095-8312.1991.tb00602.x

出版商:Blackwell Publishing Ltd    

年代:1991

数据来源: WILEY