摘要:

Eggs of the chicken turtle (Deirochelys reticularia) were collected in South Carolina from clutches laid in the spring and fall. Clutch size averaged 8.0 eggs (2 SE = 1.6; n = 15) and was weakly correlated with body size of the female. Wet mass of the clutch averaged 72.4 g (2 SE = 11.6, n = 15). There were no significant differences in clutch size or wet mass between spring and fall nesting seasons. Individual eggs laid in the fall (° = 10.7 g) were significantly larger than those laid in the spring (° = 8.5 g). Fifteen eggs laid in the spring and incubated at 29° ± 2°C averaged 152 d to hatching. Hatchling plastron length averaged 24.3 mm, and body wet mass was 6.7 g. Hatchlings (dry mass) contained 27.4% lipid, and the lipids remaining in the neonate at hatching represented 61% of the lipids originally present in the egg. The wet mass of hatchling is highly correlated with wet mass of the egg. In contrast to clutch size, egg size had a strong positive relationship to body size. A morphological constraint, the width of the pelvic canal, is proposed as having an influence on this relationship. The negative relationship between an optimized egg size and clutch size was not evident, so current optimality models do not appear to be applicable to Deirochelys.

ISSN:0012-9658    

DOI:10.2307/1939959

出版商:Ecological Society of America    

年代:1983

数据来源: WILEY

摘要:

Levels of herbivory on young and mature leaves were determined for two tree species, Trichilia cipo (Meliaceae) and Cecropia insignis (Moraceae), in a lowland rain forest of Panama. Saplings of both species were studies in light gaps, and in addition, Trichilia was studies in the understory. Rates of leaf damage by insects were measured on marked plants during four 3—wk sample periods conducted at 5—mo intervals. Mature leaves of Cecropia suffered average damage rates that were five times greater than those suffered by Trichilia; the reverse was true for young leaves. Patterns of intraspecific variation in herbivory on mature leaves were similar for the two species, despite differences in life history, habitat, defensive characteristics, and levels of damage. Variation among individuals at any one sample period was high. Damage levels during sequential samples were not significantly correlated within an individual but were highly variable. For each sample period, a different group of individuals (with one exception) comprised the 20% most heavily grazed. These patterns of herbivory are discussed with respect to seasonal effects, possible causal mechanisms, and implications for escape of herbivores and selection of defenses.

ISSN:0012-9658    

DOI:10.2307/1939960

出版商:Ecological Society of America    

年代:1983

数据来源: WILEY

摘要:

Over a 20—yr period, 1959—60 to 1979—80, rhesus monkey populations in agricultural areas of northern India declined substantially. Roadside populations decreased 77%, from 5.7 rhesus groups to 1.3 groups/100 km. Canal bank populations declined 76% from 11.5 to 2.8 groups/100 km. Village populations of rhesus declined 89%, and a new sample of 245 additional villages in 1979—80 revealed no rhesus monkeys in or near these villages. Rhesus groups in towns showed the least decline: 24% over the past 20 yr. A few localities in India continue to have abundant rhesus. Banda District in southern Uttar Pradesh had one village with more than twice as many rhesus in 1979—80 as in 1959—60 (11 rhesus groups with 267 monkeys in 1980 compared to only 5 groups with 109 monkeys in 1960), but all of these groups were associated with Hindu temples or a sacred hill. In other sites of religious significance for Hindus, including temple areas around Ajodhya in central U.P., rhesus have declined over 90%. Although a few localities and special sites in India still have good populations of rhesus monkeys, they are no longer a common or widespread feature of agricultural India.

ISSN:0012-9658    

DOI:10.2307/1939961

出版商:Ecological Society of America    

年代:1983

数据来源: WILEY

摘要:

Growth of stonefly nymphs was investigated in Ovre Heimdalsvatn, a subalpine lake a 1090 m above sea level in the Jotunheimen Mountains of central southern Norway. The lake is ice covered from mid—October until early June. Four species, Nemoura cinerea, Nemoura avicularis, Capnia atra, and Diura bicaudata, were studied at regular intervals over a 2—yr period. Nymphal growth curves were divided into periods during which exponential growth was constant. Specific growth rates were measured in terms of both length (GL) and dry mass (GM). The following respective ranges of GLand GMwere recorded: N. cinerea, 0.3—1.5 and 0.8—3.6%/d; N. avicularis, 0.2—0.7 and 0.3—1.1%/d; C. atra 0.1—1.3 and 0.3—3.6%d; bicaudata, 0.2—1.7 and 0.8—5.9%/d. While most species had low specific growth rates (GM= 0.3—0.9%/d) during ice cover, C. atra had a growth rate (GM) of 1.6%/d when the mean water temperature was only 0.6°C. There were no significant differences between the growth rates in the 2 yr for each particular period of constant growth. However, there was considerable variation in growth rate throughout the year, there being a strong positive correlation (P<.001) and a monotonically increasing relationship between specific growth rate and mean water temperature.

ISSN:0012-9658    

DOI:10.2307/1939962

出版商:Ecological Society of America    

年代:1983

数据来源: WILEY

摘要:

Changes were recorded in population and species density of a 3—ha permanent Trachypogon savanna plot, protected against fire and cattle grazing for 16 yr (1961—1977). This savanna is a grassland (mainly Trachypogon species), with scattered trees and groves. Under protection it is gradually changing into a denser arboreal community; trees in the grassland and in the groves increased 14.6— and 3.7—fold, respectively. In places, ironstone outcrops limit woody plant invasion and prevent the whole area from developing into a savanna woodland. Experimental explosions (using dynamite) in the ironstone outcrop led to the growth of trees in soil pockets formed in the artificial fissures.

ISSN:0012-9658    

DOI:10.2307/1939963

出版商:Ecological Society of America    

年代:1983

数据来源: WILEY

摘要:

Attention is drawn to some useful but not generally known properties of principal components analysis (PCA). Noncentered PCA of proportion data gives site ordinations that display approximate alpha diversities of sites and beta diversities of groups of sites, as measured by the Simpson index and mean squared Euclidean distance, respectively. Species centering allows a better approximation to beta diversities. Alpha diversities can still be visualized after centering if the true origin is projected into the plane of the ordination. The approximate species composition of each site can also be visualized if the site ordination is combined with a species ordination. The resulting plot of site scores and species loadings is called a PCA biplot. Finally, in a PCA biplot that displays both species composition and diversity, diversity values can be explained in terms of the main species contributing to diversity. In such a biplot the sum of squares of the species loadings must be scaled to unity, while the site scores must be scaled to a sum of squares equal to the corresponding eigenvalue. This type of biplot is termed a "distance biplot." For a simple illustration noncentered and species—centered distance biplots were produced for some diatom samples taken from Dutch moorland pools in the 1920s and 1978. The distance biplot is concluded to be among the most powerful analytical tools for species—composition data and derives some of its power from properties not possessed by, for example, reciprocal averaging. One problem is that it attaches little weight to rare species, but this problem can be solved by various possible data transformations based on the theory of diversity indices.

ISSN:0012-9658    

DOI:10.2307/1939964

出版商:Ecological Society of America    

年代:1983

数据来源: WILEY

摘要:

Seasonal differences in the body temperatures (Tb) of free—ranging Galapagos land iguanas (Conolophus pallidus) were detected by temperature sensitive telemetry transmitters. Midday Tb's of iguanas average 4.4°C lower in the Garua (cool) season than in the Hot season. Measured Tb's and those predicted from biophysical models permitted the following conclusions: (1) lower Tb's during the Garua season represent an active shift in thermoregulation by the iguanas rather than a passive result of a cooler season; (2) the average midday Tbselected by the iguanas in either season is the Tbthat allows maintenance of a constant Tbfor the longest possible portion of the day; (3) by exploiting the warmer microclimate created by a cliff face, the iguanas are able to maintain a constant Tbfor a full hour longer than they could elsewhere in their home range. Census data demonstrated that the iguanas exploited the warmer microclimate created by the cliff extensively during the Garua season, and the cliff face was visited by the iguanas relatively infrequently during the Hot season. Thus, the exploitation of the microclimate created by the cliff results in seasonal differences in the pattern of space utilization within the home ranges of the iguanas. Within the Garua season the iguanas moved away from the cliff more often on sunny days than during cloudy days. It is concluded that the physical environment is an important determinant of patterns of space utilization both within and between seasons.

ISSN:0012-9658    

DOI:10.2307/1939965

出版商:Ecological Society of America    

年代:1983

数据来源: WILEY

摘要:

In even—aged monocultures, distributions of seedling mass shift from symmetric to right—skewed as plants grow. One explanation for the shift is that numerous small individuals and few large ones reveal underlying dominance and suppression caused by depletion of resources. A second explanation is that the asymmetry represents a shift from normal to lognormal mass distributions because of variance in exponential growth rate. As a consequence of the first mechanism but not the second, the presence of resource depletion should increase both the skewness and the variance of distributions of individual plant mass. Even—aged populations of the prairie grass Festuca paradoxa were grown in the greenhouse for 44 d with and without competition (dense flats or one individual to a container), and with and without augmented nutrients. At each harvest, plants grown densely were smaller than isolated plants, demonstrating that resource depletion occurred. Distributions of mass of isolated plants skewed first and remained more highly skewed throughout the experiment. At a given mean mass, the standard deviation of mass for crowded and isolated plants did not differ. At a given mean mass, the skewness of mass for crowded plants was not greater than for isolated ones. The second explanation is supported, and shifts in distribution shape can be attributed to growth alone, in the absence of dominance and suppression. Competition in this case did not promote skewing but actually retarded its appearances. Consistency of these results with previous findings is discussed.

ISSN:0012-9658    

DOI:10.2307/1939966

出版商:Ecological Society of America    

年代:1983

数据来源: WILEY

摘要:

At the end of their breeding season, male side—blotched lizards, Uta stansburiana, from western Colorado decreased their home range to a size not different from that of females. Both males and females showed a high degree of overlap in home ranges, not found in populations previously studied in Texas. Uta's sprint speed was dependent on body temperature, with maximum sprint speed occurring at body temperatures between 35° and 38°C, with lower speeds at higher and lower temperatures. An energy budget model was used to predict the range of body temperatures (and thus sprint speeds) available to lizards in four microhabitats within each animal's home range. Predicted body temperatures were converted to a space—time index. The distribution of the space—time index in each microhabitat was used to predict the spatial and temporal distributions of lizards. Predicted distributions accurately reflected the measured distributions of lizards in the morning and late afternoon, but did not reflect the measured distributions during midday. These inconsistencies are thought to be the result of lizard responses to other temperature—dependent processes, such as evaporative water loss.

ISSN:0012-9658    

DOI:10.2307/1939967

出版商:Ecological Society of America    

年代:1983

数据来源: WILEY

摘要:

The vegetation and soil chemistry of 15 abandoned mounds of Formica canadensis were compared to control quadrats in a meadow at 2900 m near Gothic, Colorado, USA. Principal Components Analysis indicated the mound vegetation was relatively homogeneous and distinct from nonmound vegetation. Discriminant Analysis indicated that mounds were characterized by Bromus polyanthus and Achillea millefolium, and nonmounds by Poa interior. A parallel analysis of 15 soil chemicals indicated some statistically significant chemical differences between mounds and nonmounds. Several micronutrients (Fe, Zn, Mn), were lower in mounds but were unlikely to be deficient. Ant—dispersed plants (myrmecochores) were almost entirely restricted to nonmound quadrats.

ISSN:0012-9658    

DOI:10.2307/1939968

出版商:Ecological Society of America    

年代:1983

数据来源: WILEY