摘要:

In adjacent areas of broadleaf evergreen forest, deciduous dipterocarp forest, and agricultural land in northeastern Thailand,>4,000 individuals of 105 species of reptiles and amphibians were systematically collected. The position of capture of each individual was recorded in terms of a complex microhabitat code. The 3 environments differ substantially in pattern of human disturbance, in vegetation structure, and in range and predictability of temperature and total evaporation, the evergreen forest having the most buffered climate near the ground. Of the 3 environments studied, the evergreen forest has the most diverse and distinct herpetofauna, and the largest percentage of autochthonous species. The evergreen forest community has more southern or tropical affinities, while the deciduous forest community has more northern affinities. Analysis of the use of microhabitat categories by coexisting species reveals significant differences, even among the most similar sets of species. Differences in species richness among the three communities are not explained by differences in microhabitat diversity, mean niche breadth, or mean niche overlap. However, an ith nearest neighbor analysis of the dispersion of niche centers in resource space reveals closer packing and larger and more distinct guilds in the evergreen forest: the environment richest in species and the most predictable in climate. Both a graphical treatment and an analysis of sets of species grouped a priori according to their general natural history confirm the existence of larger and significantly tighter guilds in the evergreen forest. It is suggested that unpredictable environments tend to prevent the formation of distinct guilds, while the greater species richness of more predictable environments may be a function of guild formation.

ISSN:0012-9615    

DOI:10.2307/1942516

出版商:Ecological Society of America    

年代:1977

数据来源: WILEY

摘要:

Niche relationships between the desert mule deer (Odocoileus hemionus crooki) and Coues white—tailed deer (Odocoileus virginianus couesi) were studied in the San Cayetano and Dos Cabezas mountains in southeastern Arizona from September 1969 to March 1972. Walk transects were established on the study areas on which deer were observed. Altitude, slope exposure, and habitat selection were used to describe distributional patterns of the two species. Food habits were studied by analyzing fecal samples microscopically for epidermal fragments of important forage plants. Behavioral interaction between mule deer and white—tailed deer, browse utilization on Cercocarpos breviflorus, and recruitment were also investigated. Spatial distributions according to altitude and slope exposure indicated that a 'buffer' zone existed between populations of mule deer and white—tailed deer in the San Cayetano Mountains. Mule deer were associated with fewer vegetational types than white—tailed deer on this study area; Prosopis juliflora and Fouquieria splendens were indicative of mule deer habitat. White—tailed deer utilized a greater diversity of vegetational types in the San Cayetanos and did not appear to be associated with any particular plant species, although Quercus oblongifolia, Dasylirion wheeleri, and Eysenharditia polystachya were important. The most important forage plants for white—tailed deer in the San Cayetano Mountains were E. polystachya, Eriogonum wrightii, Krameria parvifolia, and Fendlera rupicola. Similarly, the primary food items of mule deer were E. polystachya, Calliandra eriophylla, and K. parvifolia. There was much overlap in food preferences of mule deer and white—tailed deer (55% to 67% seasonally) particularly on E. polystachya and K. parvifolia. Populations of mule deer and white—tailed deer were sympatric in the Dos Cabezas Mountains; the coefficients of association were highly positive. There was also a great similarity in habitat selection between the two species. Both species were associated with those habitat types dominated by Quercus emoryi, Juniperus deppeana, C. breviflorus, Quercus gambelii, Nolina microcarpa, Symphoricarpos ereophilus, and/or Bouteloua spp. White—tailed deer displayed a greater preference for the Quercus Symphoricarpos and Quercus—Cercocarpus habitat types than mule deer, whereas Juniperus—Cercocarpus habitats were preferred more by mule deer. Food habits of mule deer and white—tailed deer were very similar: all plant species important to white—tailed deer were also important to mule deer. The most frequent forage plants, in order of importance, were C. breviflorus, E. wrightii, J. deppeana, and Q. gambelii. Recruitment to the population was higher for mule deer than for white—tailed deer. Utilization of the annual leader growth on the key browse plant (C. breviflorus) was extremely high. Mule deer were dominant over white—tailed deer in all behavioral interactions observed during the study. In half of these instances, mule deer displayed aggressive threat in asserting their dominance; the rest were of a passive nature. The low coefficients of distributional overlap and high indices of overlap in food habits for the San Cayetano Mountains lead us to conclude that mule deer and white—tailed deer competitively exclude each other. The high overlap in spatial distributions, habitat selection, and food habits coupled with the high utilization of the key forage plant (C. breviflorus) in the Dos Cabezas Mountains during the winter months lead to the conclusion that direct competition between the two species probably was occurring during that time. This direct competition can be explained on the basis that it is a temporary phenomenon. It is hypothesized that the factors that have brought mule deer and white—tailed deer into direct competition in this area have been vegetational changes, livestock overgrazing and/or range fire suppression.

ISSN:0012-9615    

DOI:10.2307/1942517

出版商:Ecological Society of America    

年代:1977

数据来源: WILEY

摘要:

After metamorphosis, smooth or common newts (Triturus vulgaris vulgaris [Linn]) disperse on land, where they live as juveniles before returning to the water as breeding adults. The population age—structure was obtained by dissecting the standard length frequency distribution, a procedure which is justified in the text. Juveniles have an uncomplicated age—structure, the number of individuals in successively later age—classes being reduced by mortality and by recruitment to the adult population. Among adult newts, the most frequent age—class is nearly central, indicating the existence of extensive variation in the age at maturity. Growth continues throughout life, the rate of growth decreasing with age. The annual survival rate of adult newts as estimated by a census method, and from the age—structure, was found to be ~ 50%, being rather greater in ♀ ♀ than in ♂ ♂. Less reliable data indicate the annual survival rate of juveniles was ~ 80%. Maturity is attained between the ages of 3 and 7 yr, most individuals reproducing for the first time at 6 or 7 yr of age. The number of eggs laid increases with age from ~ 100 at age 3 to ~ 400 at age 12; there is also an effect of ♀ age on oocyte size, which may influence subsequent larval survival. Smooth newts breed annually. Reproduction diverts surplus energy from somatic growth, and thereby decreases potential future fecundity in animals whose fecundity is proportional to body size. Individuals maturing at different ages, therefore, have different schedules of fecundity, which were estimated through the use of microbomb calorimetry. Population size was found to be lognormally distributed, with a mean of ~ 70. The sex ratio of juvenile newts was near equality, but a majority of ♀ ♀ comprised most adult populations. This imbalance is due to greater mortality of adult ♂ ♂, which results in an age—specific trend in the sex ratio. There are 2 breeding migrations: 1 in autumn and 1 in spring. It is likely that newts migrate during autumn when about to reproduce for the first time, and thereafter migrate during spring. Terrestrial newts appear to move little; there is some evidence that colonization of newly dug ponds is achieved by the infrequent emigration of juveniles. During its life, a smooth newt occupies a succession of ecological niches. Moreover, different individuals may occupy different niches, or may occupy the same niches for different periods of time. It is speculated that in large newt populations the complex life history is able to trap genetic variation and to dampen fluctuations in population size. However, it is suggested that these group attributes have arisen largely as the result of selection between individuals. Breeding only once (rather than repeatedly) will reduce fitness because the additional fecundity necessary to balance the loss of later reproduction cannot be attained. Early maturity appears to be favored in ♂ ♂ and late maturity in ♂ ♂ these opposed selection pressures may contribute to the observed age variation at maturity. Finally, the sex ratio does not vary with population density, and is therefore thought to be controlled by natural selection.

ISSN:0012-9615    

DOI:10.2307/1942518

出版商:Ecological Society of America    

年代:1977

数据来源: WILEY

摘要:

The invasion of Mesembryanthemum crystallinum into coastal grassland was observed at Surf on the central coast of California, USA. The species became established in areas unoccupied or sparsely occupied by other plants, and then grew into surrounding areas. The following season, few grassland seedlings established beneath dried Mesembryanthemum as compared to adjacent grassland. The reduction in numbers of grassland seedlings did not appear to be the result of limiting levels of moisture, light or macronutrients which were found in lower levels in the grassland, nor to be due to grazing by small mammals, since the pattern persisted in the absence of grazing. The differential pattern of seedling establishment was correlated with high levels of salt found in the soil beneath dried Mesembryanthemum. Mesembryanthemum crystallinum is an annual plant which accumulates salt throughout its lifespan. After the plant dies, this salt is released with leaching by fog and rain. The salt produces a detrimental osmotic environment preventing growth of nontolerant species. The salt does not appear to have a direct toxic influence on grassland species. Osmotic interference resulting from accumulation and release of salt appears to be the means by which Mesembryanthemum crystallinum dominates areas previously occupied by grassland.

ISSN:0012-9615    

DOI:10.2307/1942519

出版商:Ecological Society of America    

年代:1977

数据来源: WILEY

摘要:

A breeding population of the Weddell seal (Leptonychotes weddelli) was studied annually during the 2 1/2—mo pupping and breeding season in McMurdo Sound, Antarctica, from 1969 through 1974. Components of the population were estimated by direct counts of adult ♂ ♂ with pups, by capture—recapture studies of nonparous ♀ ♀ and adult ♂ ♂, and by aerial counting. Total population size was estimated as being on the order of 2,500—3,000 seals. The Seber—Jolly method was adapted to circumstances of the present study. Reproductive rates (measured in terms of successful pupping) were ~ 0.5 pups/♀ for the entire breeding colony, and ~ 0.7 pups/♀ for a subset of tagged ♀ ♀ observed for 4 yr in sequence. Age—specific reproductive data were also obtained, and it appears that full reproductive activity of ♀ ♀ is achieved at ~ age 7. The annual survival rate for adult ♀ ♀ is in the range of 0.80 to 0.85, as determined (by several methods) from tagging data. Survival rates for adult ♂ ♂ are lower (perhaps 0.50), but are not as well established. Little information was obtained on the subadult class (1 to 3 yr of age). Underwater territories of adult °° on one breeding colony were studied by acoustic tagging and found to be steadily patrolled by dominant ♂ ♂.Two experimental colonies having different densities ties of ♂ ♂ with pups demonstrated increased interactions at higher densities, but lower weight losses on the part of the °° (presumably due to isolated location of the colonies). We infer from the available data that the McMurdo Sound population is somehow regulated by a physiological or social connection between the number of adult ♀ ♀ at the pupping colonies and subsequent years' pup population.

ISSN:0012-9615    

DOI:10.2307/1942520

出版商:Ecological Society of America    

年代:1977

数据来源: WILEY