ISSN:0012-9658    

DOI:10.2307/1934811

出版商:Ecological Society of America    

年代:1976

数据来源: WILEY

摘要:

Behavioral and demographic parameters were studied in Microtus longicaudus and M. mexicanus during 1969 and 1970. Microtus longicaudus was at peak density (120/ha) in 1969 and decline density (30/ha) in 1970. Microtus mexicanus remained at low density (30/ha) during both years. Sex ratios, and survival rates were different between years in M. longicaudus, not different in M. mexicanus. Intraspecific agonistic behavior in M. longicaudus was consistent with hypotheses of intrinsic regulation. Behavioral reactions related to contention for space were measured. These values support an hypothesis relating space to interspecific competition in these species.

ISSN:0012-9658    

DOI:10.2307/1934812

出版商:Ecological Society of America    

年代:1976

数据来源: WILEY

摘要:

Two sympatric species of Plenthodon (P. hoffmani and P. punctatus), dissimilar in size as adults, were used to investigate the general problem of how two species that differ in size as adults but overlap in certain life history stages may avoid significant, size—related overlap in ecological requirements. The following three hypotheses were tested: (1) that size differences between adults lead to resource partitioning adequate to explain the coexistence of adults; (2) that co—occurring, similarly sized juveniles of the large species and adults of the smaller lack significant resource partitioning; and (3) that alternatives to resource partitioning are likely to be of importance in promoting coexistence in these salamanders. Analysis of food and surface habitat utilization shows overlap values that are low enough for adults of the two species to coexist but too high for coexistence between juveniles of the larger species and adults of the smaller. Because subadults and juveniles make up a substantial proportion of the population of the largest species, it appears that salamanders with long developmental periods and without temporal staggering during periods of development, probably cannot use adult size differences alone as an avenue along which to ameliorate interspecific competition for food or space. On the other hand staggered feeding schedules (noncoincident feeding) in all individuals, coupled with the partioning of the structural habitat by adults of the two species, appear to be factors of major importance in reducing inter— and intraspecific competition.

ISSN:0012-9658    

DOI:10.2307/1934813

出版商:Ecological Society of America    

年代:1976

数据来源: WILEY

摘要:

Comparisons were made of the energy budgets of three ectothermic vertebrates found in the Southeastern United States. The three species studied were Elaphe guttata (corn snakes), Heterodon platyrhinos (eastern hognose snakes), and Bufo terrestris (southern toads). Values for assimilation efficiency, ingestion, excretion, growth, shedding, metabolism, and reproduction were converted to caloric units and integrated into energy flow models for each species.

ISSN:0012-9658    

DOI:10.2307/1934814

出版商:Ecological Society of America    

年代:1976

数据来源: WILEY

摘要:

The limpet Acmaea insessa lives on and east only the kelp Egregia. In the intertidal zone around Santa Barbara, California, USA the grazing activities of this limpet caused extensive and conspicuous damage to the majority of the larger Egregia. Severe damage weakened the main axis of the algae and was associated not only with loss of parts of Egregia, but also with one—third of the individuals found cast ashore; the remaining two—thirds suffered detachment from the substratum. The distribution of Acmaea insessa among Egregia was not uniform. Settlement of the limpet on experimental groups of algae was greater on old, post—reproductive Egregia than on new Egregia, was greater on crowded algae than on isolated algae, and was greater on individuals with adult limpets already on them than on individuals without limpets. The density of limpets increased with increasing algal length. Results of these settlement patterns were that crowded algae suffered limpet—related mortality than isolated algae, and loss of parts of individuals was more prevalent among large algae. These risks associated with loss and mortality of Egregia were countered by better survival and faster growth of small limpets in grazing scars than on intact surfaces. Experimental tests of other effects of limpet on Egregia revealed that damage by the limpet did not affect growth rate of algae or the timing and numbers of reproductive sporophylls. However, Egregia did respond to loss of parts by producing more branch rachises than those plants remaining intact. Evidence from this and other studies suggests that, although isolated Egregia suffered less mortality from limpets and had several other advantages over crowded algae, their large size was associated with mortality by detachment which may have balanced or outweighed the advantages of isolation. Loss of rachises because of grazing damage, a form of pruning by the limpet, could have served the beneficial function of preventing an Egregia from becoming so large that it was susceptible to detachment. Egregia has several escape mechanisms from the prudent predator Acmaea insessa.

ISSN:0012-9658    

DOI:10.2307/1934815

出版商:Ecological Society of America    

年代:1976

数据来源: WILEY

摘要:

The recovery patterns of hermatypic corals following an unpredicted catastrophic low tide were studied on two reef flats in the northern Gulf of Eilat, Red Sea: (1) the nature reserve of Eilat, Israel which is chronically polluted, and (b) a control reef which is pollution—free. The coral community structure and species diversity in both reefs were studied in 1969 and served as a base for comparing the extent of mortality during the low tide (1970), and the extent of recovery 3 years later (1973). In 1969 no significant differences were found (p>0.05) between the coral community structure of the nature reserve and the control reef when the average number of species, number of colonies, living coverage, and diversity (H'n) per transect were taken into account. During the low tide both reefs suffered mass mortalities of corals (85% at the nature reserve and 81% at the control reef). Although the extent of mortality in both reefs did not differ significantly (p>0.05), a marked difference was observed in their recovery 3 years later. The extent of coral recolonization was 23 X greater at the control reef, but no significant difference (p 0.05) was found in the extent of coral community regeneration in both places (15% at the nature reserve and 19.2% at the control reef). While the number of colonies, number of species, living coverage, and H'nare drastically decreased at the nature reserve 3 years after the catastrophic low tide, the control reef exhibited an outstanding fast recovery (full recovery is expected 5—6 years from the low tide). The commonest species on the control reef in 1969 showed the highest rates of recruitment in 1973, which might indicate the opportunistic life history of these species. I conclude that one of the differences between man—made polluting activities and natural catastrophes on coral reefs, is the possibility that the human—perturbed environment will not return to its former configuration, while reconstruction of reef areas denuded by natural disturbances is mainly a function of time. The higher coral diversity recorded on the control reef in 1973 (H'N= 2.403) as compared to 1969 (H'N= 2.206) may reflect a succession pattern in which diversity continues to increase in time after a catastrophe, until space becomes limiting and competitive interactions between species cause a decline in diversity. The unpredictable and extremely low tides at the Gulf of Eilat seem to interfere with this scheme and prevent monopolization of the reef flat by competitively superior species. I suggest that catastrophic low tides act as an important diversifying force on the reef flats of Eilat, in a similar way as other biological and physical disturbances affect coral communities (Porter 1974)

ISSN:0012-9658    

DOI:10.2307/1934816

出版商:Ecological Society of America    

年代:1976

数据来源: WILEY

摘要:

Between 1969 and 1972 and during 1974 I obtained data on population density, territory size, habitat, food taken, and food available to four species of Dendroica warblers (Parulidae). Densities usually were: Black—throated Green (D. virens)>Blackburnian (D. fusca)>Yellow—rumped (D. coronata)>Magnolia (D. magnolia). Black—throated Green Warblers were commoner in red spruces than in white spruces; they showed a preference for red spruce foilage. Populations of all four species were stable between 1969 and 1972, but following two poor breeding seasons populations declined in several areas. Species with dense populations had small territories and vice versa. Territory sizes of Black—throated Green Warblers in red spruces were smaller than in white spruces. Territory size usually fluctuated even less than population density, although some territories eventually increased markedly after strong declines in abundance. The food supply usually peaked in early July. Food was more abundant in white spruces than red spruces early in June but did not consistently differ subsequently. Warblers took lepidopteran larvae in preference to other prey. The number of Dendroica species in an area was closely related to the physical characteristics of the forest, but interactions among these species mediated many of the differences in density or species composition. Mature undistributed forests in this geographic area support four of these species on a long—term basis.

ISSN:0012-9658    

DOI:10.2307/1934817

出版商:Ecological Society of America    

年代:1976

数据来源: WILEY

摘要:

The feeding ecology of five oribatid mite taxa from an aspen woodland soil was examined. Ceratozetes kananaskis, Ceratozetes gracilis, and Scheloribates spp. were predominant in the fermentation (F) and humus (H) horizons while Eremaeus spp. and Eupterotegaeus rostratus were restricted to the litter (L) horizon. In laboratory studies the five mite taxa were fed and reared upon the seven most common fungal species which had been isolated from the aspen soil. The mite inhabitants of the F and H—horizons showed variation in amount of feeding and reproductive success among the fungi tested. There was no direct relationship between the amount of mite feeding and reproductive success on any given fungus. The L inhabitants fed very little on fungus in culture and showed no reproduction. Gut content analyses from field specimens showed that all taxa fed on fungi and demonstrated that laboratory feeding studies were a poor indication of feeding type. All taxa fed predominately on the pigmented fungi with the F and H inhabitants showing a higher proportion of hyaline fungi than the L inhabitants; this difference was probably related to the fungal distribution in the soil. Seasonal variation in amount of gut contents was directly related to a postulated level of microbial activity in the soil. Only 2% of the fungal standing crop would be consumed in 1 yr by the total oribatid mite community emphasizing the importance of assessing the effect of the oribatid mites in conjunction with the other mycophagous members of the soil fauna. Possible interactions between oribatid mites and the fungal community were given and the consequences of the interactions related to organic matter decomposition.

ISSN:0012-9658    

DOI:10.2307/1934818

出版商:Ecological Society of America    

年代:1976

数据来源: WILEY

摘要:

Body size of chuckwallas, Sauromalus obesus (measured as the upper decile snout—vent length, UDL) at 12 locations throughout the species' range is highly correlated with average winter rainfall. The coefficient of variation of rainfall and average seasonal temperatures did not significantly aid winter rainfall in accounting for populational body size differences. Two populations with the highest (Little Lake) and the next to lowest (Amboy) UDL were studied in detail. The larger Little Lake chuckwallas appear to grow faster but do not live longer than chuckwallas at Amboy. This enhanced growth was allied to the more diverse and abundant food regime at Little Lake. Surprisingly, chuckwallas at Little Lake maintain relatively smaller fat bodies than animals at Amboy. This may be an adaptation to Amboy's more severe and less productive environment.

ISSN:0012-9658    

DOI:10.2307/1934819

出版商:Ecological Society of America    

年代:1976

数据来源: WILEY

摘要:

Root exudates from the unsuberized tips of new woody roots were collected from mature Betula alleghaniensis, Fagus grandifolia, and Acer saccharum in a northern hardwood forest. Numbers of new woody root tips were also determined for these three species. Exudates were fractioned into carbohydrates, amino acids/amides, organic acids, and 9 inorganic ions. Considerable species variation characterized the quantitative and qualitative nature of the organic fraction. Organic acids were the most abundant component. Fagus grandifolia released the largest amount of amino and organic acids per hectare, while B. alleghaniensis exuded the largest amount of carbohydrates. Sodium (possibly anomalous), K, and Ca dominated the cationic fraction, while the anionic fraction was chiefly SO4and Cl. Betula alleghaniensis and F. grandifolia released considerably greater quantities of inorganic ions than A. saccharum, but the inorganic root exudate patterns of the three species were relatively uniform. These results indicate root exudates have some role in intrasystem nutrient cycling.

ISSN:0012-9658    

DOI:10.2307/1934820

出版商:Ecological Society of America    

年代:1976

数据来源: WILEY