Showing papers in "Ecology in 1979"
TL;DR: Ecology is currently published by The Ecological Society of America and your use of the JSTOR archive indicates your acceptance of JSTor's Terms and Conditions of Use, available at http://www.jstor.org/about/terms.html.
Abstract: Ecology is currently published by The Ecological Society of America. Your use of the JSTOR archive indicates your acceptance of JSTOR's Terms and Conditions of Use, available at http://www.jstor.org/about/terms.html. JSTOR's Terms and Conditions of Use provides, in part, that unless you have obtained prior permission, you may not download an entire issue of a journal or multiple copies of articles, and you may use content in the JSTOR archive only for your personal, non-commercial use. Please contact the publisher regarding any further use of this work. Publisher contact information may be obtained at http://www.jstor.org/journals/esa.html. Each copy of any part of a JSTOR transmission must contain the same copyright notice that appears on the screen or printed page of such transmission. JSTOR is an independent not-for-profit organization dedicated to creating and preserving a digital archive of scholarly journals. For more information regarding JSTOR, please contact support@jstor.org. http://www.jstor.org/ Thu Feb 2 13:29:01 2006
1,089 citations
TL;DR: The effects of disturbance on local species diversity were investigated in an algal- dominated intertidal boulder field in southern California and suggest that disturbances which open space are necessary for the maintenance of diversity in most commu- nities of sessile organisms.
Abstract: The effects of disturbance on local species diversity were investigated in an algal- dominated intertidal boulder field in southern California. In this habitat, the major form of disturbance occurs when waves, generated by winter storms, overturn boulders. These natural physical distur- bances open space, interrupt successional sequences, and determine local levels of species diversity. Because small boulders are more frequently overturned than larger ones, the plants and sessile animals of boulder fields are distributed in a patchwork of successional stages. Boulders which are subjected to intermediate disturbance frequencies are usually less dominated than those which are very frequently disturbed, and always less dominated than those which are seldom disturbed. In all seasons most small boulders have fewer species than those of intermediate size. Large boulders also usually have fewer species, except in the spring, when defoliation of the algal canopy during the previous winter has opened space for colonization. Species richness on these boulders declines during summer months, and is less than that on boulders of intermediate size in the fall. Small boulders, with a shorter disturbance interval, support only sparse early successional com- munities of the green alga, U/va, and barnacles. Large, infrequently disturbed boulders are dominated by the late successional red alga, Gigartina canaliculata. Intermediate-sized boulders support the most diverse communities composed of U/va, barnacles, several middle successional species of red algae, and Gigartina canaliclaata. Comparison of the pattern of succession on experimentally sta- bilized boulders with that on unstable ones confirms that differences in the frequency of disturbance are responsible for the above patterns of species composition. The frequency of disturbance also determines the degree of between-boulder variation in species composition and diversity. Small boulders which are frequently overturned sample the available pool of spores and larvae more often. As a result, a greater number of different species occur as single dominants on these boulders. Boulders with an intermediate probability of being disturbed are most variable in species diversity. Assemblages on these boulders range from being dominated by a single species to being very diverse while most communities on boulders which are frequently or seldom disturbed are strongly dominated. Observations on the local densities of three species of middle successional red algae over two year-long periods indicate that most of these are variable in time. More local populations went extinct or became newly established on boulders than remained constant in size. These species persist glob- ally in the boulder field mosaic by colonizing recent openings created by disturbances. These results lend support to a nonequilibrium view of community structure and, along with other studies suggest that disturbances which open space are necessary for the maintenance of diversity in most commu- nities of sessile organisms.
1,010 citations
TL;DR: A model is given for multiple recapture studies on closed populations which allows capture probabilities to vary among individuals and a nonparametric estimation procedure for population size is given that is robust to moderate variations in individual capture probabilities which may occur in commonly used short—term livetrapping studies.
Abstract: A model is given for multiple recapture studies on closed populations which allows capture probabilities to vary among individuals. The capture probability of each individual is assumed to be constant over time. Based on this model we give a nonparametric estimation procedure for population size. The estimator involves selecting one of a sequence of estimators which are each linear combinations of the capture frequencies. The individual estimators are derived from the generalized jackknife method. We also give a goodness of fit test for the model's assumption that individual capture probabilities do not change during the study. The robustness of this estimation procedure is investigated with a simulation study. By virtue of this study, and the theoretical nature of the estimator, it is judged to be robust to moderate variations in individual capture probabilities which may occur in commonly used short—term livetrapping studies. See full-text article at JSTOR
840 citations
TL;DR: While trophic status and weight modify the utilizable proportion of energy in the habitat, broad correlations also exist between size of home range and surrogate variables for productivity (precipitation and latitude).
Abstract: Area of home range (H) can be related empirically to body weight (W) by the formu- lation H = a Wk. The computed values of exponent k have generated controversy concerning potential differences between trophic groups and whether they differ from 0.75 (the value expected if area of home range is a function of basal metabolic rate). When large mammals are considered, the empirical relationship assumes the form H = .002W1 02 for herbivores, H = .059W.92 for omnivores, and H = .11W136 for carnivores. By treating the animal's energetic requirements and the productivity of its habitat explicitly, empirical values of k > 0.75 are shown to result from declining rates of production of utilizable energy per unit area of habitat with increasing body weight. While trophic status and weight modify the utilizable proportion of energy in the habitat, broad correlations also exist between size of home range and surrogate variables for productivity (precipitation and latitude). Differences in weight alone account for a large portion of the differences between male and female or subadult and adult home ranges. Behavioral phenomena need not be invoked. Differences between herbivores and carnivores are in the direction suggested for birds and mammals. Criticisms regarding inter-class and inter-trophic comparisons appear resolved.
840 citations
553 citations
TL;DR: Foraging flocks of granivorous Yellow-eyed Juncos were studied for two winters to test hypothesized relationships between group size and time budgets, finding that Dominants apparently forage more efficiently than subordinates because of differences in habitat utilization and time allocation.
Abstract: Foraging flocks of granivorous Yellow-eyed Juncos (Junco phaeonotus) were studied for two winters to test hypothesized relationships between group size and time budgets Required feeding time is so large that it constrains aggression At low temperatures (high foraging requirements) a large flock forms in the area of maximal food availability Group size decreases at warmer temper- atures, since the constraints on aggression are reduced Group size variance responds similarly As group size increases, individuals scan less often for approaching predators The time saved is employed to increase feeding rates, unless aggression levels are extremely high Rates of aggressive interaction increase with group size, and with both ambient temperature and food density Dominants apparently forage more efficiently than subordinates because of differences in habitat utilization and time allocation These differences are consistent with the hypothesized correlation between increasing dominance and greater overwinter survivorship
405 citations
TL;DR: It is concluded that the most important problem faced by the foraging bees attempting to enhance food intake is that of assessing the resources, which often change rapidly.
Abstract: On their first 2 foraging trips out of the hive, young Boinhus x'iwtcans workers visited, on the average, 4 or 5 different kinds of rewarding as well as unrewarding flowers, and few of each kind in succession. But, after 3-7 foraging trips, most of the bees specialized on jewelweed, which was the most numerous flower available with high nectar reward. When jewelweed specialists became numerous, and the food rewards in jewelweed declined, the bees resampled the reward spectrum. They again visited, and continued to vist, at least 3-4 different kinds of flowers on successive foraging trips in an enclosure where patch size was limited. Flowers in open inflorescences (aster, goldenrod) were handled appropriately from the start, but handling accuracy at zygomorphic flowers jewelweedd, turtlehead) was initially 40-50% at the first 10 flowers encountered, and increased to >90%Xe in 60-100 flower visits. It is concluded that the most important problem faced by the foraging bees attempting to enhance food intake is that of assessing the resources, which often change rapidly. Individual bees specialize on flowers yielding rewards that are "perceived" to exceed some minimum. However, the difference between perceived and actual rewards is, in part, determined by handling skills that are affected by foraging experience. Thus, optimal foraging in the bees must be explored from the per- spective of long- rather than short-term energy balance.
350 citations
TL;DR: Stable carbon isotope ratio analysis appears to be a powerful tool in the evaluation of carbon pathways in estuarine food webs.
Abstract: The complex nature of, and importance of detritus consumption in, estuarine food webs make analysis of specific pathways of carbon in estuaries very difficult. We have evaluated the use of the natural abundances of the stable carbon isotopes in estuarine flora and fauna as a qualitative indicator of food sources in a Georgia salt marsh estuary. The salt marsh ecosystem is particularly amenable to this technique because of the wide span of distinctive 13C/12C ratios of the dominant plants h13C of -12 to -26%o). Laboratory experiments showed negligible further fractionation of the characteristic 813C of marsh plants during microbial degradation of dead plant material, and during assimilation of ingested detritus by estuarine invertebrates. Invertebrates having a variety of feeding habits were collected in monospecific and mixed species stands of marsh plants. Marsh snails and insects had 613C values close to those of the associated vascular plants. Deposit-feeding crabs had isotope ratios biased away from the marsh plant 613C values, likely a result of feeding on benthic diatoms and out-of-stand foraging. Mud snails and filter-feeding bivalves showed 13C/12C ratios similar to those of benthic and pelagic algae. The 613C values of marsh fiddler crabs varied from - 12 to -24%o in various habitats having predominately C4 or C3 food source plants. Individuals collected from populations of 3 crab species in a Spartina alterniflora marsh had t3C/t2C ratios with a standard deviation of only about 1%o from the mean 613C. Stable carbon isotope ratio analysis appears to be a powerful tool in the evaluation of carbon pathways in estuarine food webs.
338 citations
TL;DR: It is suggested that foraging opportunities vary with height in a forest and are influenced by the physical and chemical characteristics of the plant species, which in turn affect the kinds and distributions of foraging sub- strates, the ways in which birds search for and find food, and the abundances of food resources.
Abstract: We examined the similarities and differences in the foraging patterns of 22 insectivo- rous bird species during their breeding season in the Hubbard Brook Experimental Forest, New Hampshire, USA. Using multivariate techniques (clustering of hyperdimensional Euclidean distances, principal components analysis, and Varimax rotated factor analysis), we distinguish 4 groups of species or guilds, each of which exploits food resources in a distinctly different way. Partitioning occurs primarily by (1) foraging height and height-related characters, (2) foraging locations within the forest canopy, and (3) differential use of tree species, foraging substrates and foraging maneuvers. The results indicate that the importance of vegetation height to bird species diversity is related (1) to foraging opportunities which differ along a gradient from ground level to the upper canopy and which are roughly indexed by measures of foliage height diversity (FHD), and (2) to the presence of the supporting branch and bole framework which provides a major distinct foraging region. We suggest that foraging opportunities vary with height in a forest and are influenced by the physical and chemical characteristics of the plant species, which in turn affect the kinds and distributions of foraging sub- strates, the ways in which birds search for and find food, and the abundances of food resources. The implications of these findings for understanding the structure of forest bird communities are discussed.
337 citations
TL;DR: The patterns of habitat switching indicate that the addition of a competitor which is more effective in a given habitat can change the profitability ranking for a species to the extent that the preferred habitats are abandoned, providing mental evidence for the compression hypothesis as a mechanism for the development and maintenance of resource partitioning by habitat.
Abstract: A series of experiments are presented which elucidate competitive interactions among 3 congeneric sunfishes (Centrarchidae). In the absence of competitors all species rank 2 habitats (vegetation, sediments) in the same order according to profitability but differ in their relative effi- ciencies at utilizing these habitats. The ordinal ranking of foraging efficiencies of these species in the 2 habitats permits qualitative predictions of the occurrence and order of habitat shifts as resources decline (competitive pressure increases). We present an experiment demonstrating such habitat shifts which corroborate these predictions. The patterns of habitat switching indicate that the addition of a competitor which is more effective in a given habitat can change the profitability ranking for a species to the extent that the preferred habitats are abandoned. Thus these results provide experi- mental evidence for the compression hypothesis as a mechanism for the development and maintenance of resource partitioning by habitat. Further, the ecological flexibility exhibited by the sunfish indicates that overlap or co-utilization of habitats can be a very dynamic process, determined by the relation between resource levels and differences in foraging efficiencies among species. The implications of these results to competition, optimal use of a patchy environment, and species abundance relations in natural lakes are discussed.
336 citations
TL;DR: A clear relationship between larval growth and growth form of the food plants quantified as leaf water content was revealed, and it was found that larvae grew faster and more efficiently on herbaceous plants than on the foliage of shrubs and trees.
Abstract: Larvae of 9 species of swallowtail butterflies (Papilionidae), 10 species of bombycoid moths (Saturniidae and Bombycidae), and of the southern armyworm (Noctuidae: Spodoptera eri- dania) were reared under standardized conditions on mature leaves of many of their typical food plants. Growth rates, feeding rates and efficiencies of food and nitrogen utilization of larvae in their penultimate and final instars were measured by standard techniques. The study revealed a clear relationship between larval growth and growth form of the food plants quantified as leaf water content. Larvae grew faster and more efficiently on herbaceous plants than on the foliage of shrubs and trees. These differences were greater than could be accounted for by variation in the degree of feeding specialization among the insect species tested. The particular leaf characteristics responsible for the relationship between plant growth form and larval growth are not known, but they probably include leaf water content, nitrogen content, tough- ness, and fiber content. Since trees are likely to be more apparent to enemies than are most herbaceous plants, our results are consistent with recent suggestions that the mature foliage of apparent plants is generally poorer food for herbivores than is the foliage of unapparent plants. However, the extent to which the low food value of mature tree leaves is actually a consequence of the selective action of herbivores remains an open question.
TL;DR: Results indicate that consistent patterns do exist in the organization of these stream communities, and that the species currently living together are not a random assortment of species and do not randomly divide their resources.
Abstract: This study uses morphological data relating to many aspects of the niche to study community organization in assemblages of stream fishes from three separate drainages. Mean values for all morphological features were compared statistically for coexisting species pairs, and those features which had significantly different means were assumed to indicate ecological differentiation that exists between the species under consideration. Average niche overlap as defined by the percentage of morphological features not differing significantly between species pairs was constant for these assemblages regardless of a nearly twofold difference in number of species present. Similarly, the average Euclidean distance between the centers of morphologically defined niches for all sympatric common species was approximately the same for all three assemblages. Moreover, the distribution of Euclidean distances between species was the same in all three drainages and different than a distribution that would result from a random division of resources. Together, these results indicate that consistent patterns do exist in the organization of these stream communities, and that the species currently living together are not a random assortment of species and do not randomly divide their resources. The presence of higher numbers of species in a community seems not to be accompanied by increased packing of the niches, but rather by an occupation of more total niche space by the community as a whole.
TL;DR: A three—component competing—rick model for animal mortality is presented, in which the additive hazards include a new model, dominant during the prematurity period; a constant hazard, dominant During the period of maturity; and the conventional Gompertz hazard, dominates during senescence.
Abstract: A three—component competing—rick model for animal mortality is presented, in which the additive hazards include a new model, dominant during the prematurity period; a constant hazard, dominant during the period of maturity; and the conventional Gompertz hazard, dominant during senescence. A good fit of the model is obtained to survival data for a variety of species, with both laboratory and field data being represented. Interpretation of the model parameters in terms of animal adjustment to hazards is offered. See full-text article at JSTOR
TL;DR: Although variability characterizes most aspects of P dynamics in Bear Brook, processing of P is consistent and monthly transport patterns or annual mass balances generated from only 1 yr of record may lead to erroneous conclusions on stream ecosystem function.
Abstract: A phosphorus budget was constructed to examine P retention and processing during I yr (1974-1975) in Bear Brook, an undisturbed headwater stream in the Hubbard Brook Experimental Forest, New Hampshire, USA. Year-to-year variation in the P mass balance was also estimated for a 13-yr period using an empirical model of the annual budget. In the model, fluvial inputs and exports of P were calculated using the 13-yr record of streamflow and the regressions between P concentration and discharge developed from measurements made during 1974-1976. Precipitation and streamflow were average in the 1974-75 water year, and the relative importance of P input vectors during this year were: tributary streams (62%) > falling and blowing litter (23%) > subsurface water (10%) > precipitation (5%). Geologic export of P in stream water was the only export vector of consequence. Under these average hydrologic conditions, there was no annual net retention of P in the stream: annual inputs of 1.25 g P/i2 were essentially balanced by exports of 1.30 g P/M2. However, during most days of this year inputs exceeded exports: P accumulated, was pro- cessed in the ecosystem, and was exported during episodes of high stream discharge. Because of the pulsed nature of P flux, a mass balance provides an overestimate of the P entering functional pathways of a stream ecosystem. Over the 13-yr period (1963-1975), annual mass balances calculated with the model were variable; the ratio of P exports to inputs varied from 0.56 to 1.6 and was directly related to annual streamflow. Thus monthly transport patterns or annual mass balances generated from only 1 yr of record may lead to erroneous conclusions on stream ecosystem function. Although variability characterizes most aspects of P dynamics in Bear Brook, processing of P is consistent. Inputs of dissolved P (DP, 1 mm) exceeded exports, while exports of fine particulate P (FPP, 0.45 /.m-l mm) exceeded inputs. Thus there was a net conversion of other forms of P to the FPP fraction, which was the predominant form (62% of the total) exported downstream.
TL;DR: The short mean intervals between fires suggest that pre-1875 mixed conifer forests did not usually have heavy accumulations of litter or dense thickets of under- story trees, and that the lack of frequent, low-intensity fires has resulted in a major increase in understory forest and fuels.
Abstract: Data on the years in which fires burned, on fire frequency, and on intensity and areal extent of fires were gathered from 935 scars on 220 stumps of mixed conifer forest species in an 1800- ha study area in the Sierra Nevada, California, USA. Before 1875, fires scarred clusters of living trees every 9 yr on west-facing slopes at Redwood Mountain and every 16 yr on east-facing slopes. Mean fire-free intervals between 1700 and 1875 varied by habitat phase from 5 yr in ponderosa pine on a dry ridge to 15-18 yr in more moist sites with white fir. For most 1-ha sites, the maximum time without fire was 14-28 yr. From 1700 to 1875, fires of various sizes were found every 2-3 yr somewhere in a given drainage (not necessarily the same site) and every 5-9 yr in 3- to 16-ha sites. This compares with fires every 8-18 yr in 1-ha clusters and every 11-39 yr on individual trees. Scar records of pre- 1700 fires suggest intervals fairly comparable to those from 1700 to 1875. Evidence of fires diminished greatly after Indian burning was eliminated in the early 1870's, and such fire records became almost nonexistent after 1900, when fire suppression became more effective. Most of the pre-1875 fires were small and of low intensity. Even the larger fires were usually confined to I slope or 1 drainage area. The short mean intervals between fires suggest that pre-1875 mixed conifer forests did not usually have heavy accumulations of litter or dense thickets of under- story trees. Instead, small-acreage, low-intensity surface fires must have consumed accumulated litter at frequent intervals and at the same time killed most of the conifer regeneration which had become established since previous fires. Such frequent fires would have led to an intricate mosaic of age classes and vegetation subtypes which, in turn, insured that a subsequent fire would not burn large areas with great intensity. Intense fires which moved from crown to crown were absent in the study area for the past 400 to 2000 yr. If frequency of lightning ignition of fires over the past 50 yr is typical, ignitions by Indians must have augmented lightning-caused fires to yield the pre-1865 frequency of fires in the Sierra mixed conifer forest. Since 1900, the lack of frequent, low-intensity fires has resulted in a major increase in understory forest and fuels.
TL;DR: Overall predation rate and ant species richness were found to be positively correlated on a latitudinal scale, but this relationship broke down at the level of habitats and microhabitats.
Abstract: Predation by ants on wasp larva baits was assessed at five latitudes from 43°N to 2°S. Rates of predation were significantly greater in the tropics; that is, a food item was exploited by ants in significantly less time in the tropics than in the temperate zone. It was also found that predation rates were higher in low second—growth vegetation than in forests and higher on the ground than on vegetation, and that these differences were more pronounced in the temperature zone than in the tropics. Rates of predation occuring on buildings were lower than in natural situations at every latitude. The number of ant species taken at the baits increased from 22 at the northernmost locality to 74 at the southernmost. In all localities but the northernmost the forest habitat produced a greater diversity of species than the field habitat. There was greater degree of microhabitat specificity among ants in the tropics than in the temperate zone. The proportion of forest canopy specialists also increased toward the tropics. Overall predation rate and ant species richness were found to be positively correlated on a latitudinal scale, but this relationship broke down at the level of habitats and microhabitats.
TL;DR: For all 3 species shady habitats appear to be more suitable for juvenile development and survival than sunny habitats.
Abstract: A simple hypothesis about habitat choice by ovipositing butterflies is that females prefer to lay their eggs on plants in habitats where juvenile growth and survival are best. This hypothesis was evaluated by studying 3 Aristolochia—feeding swallowtail butterflies (Papilionidae: Troidini). Results show that the eggs and larvae of all 3 butterfly species survive significantly better in shady habitats than in sunny habitats. Pupal survival is similar in the 2 habitats for at least 1 species. Larval growth rates were similar in the 2 habitats for all 3 species. Thus, for all 3 species shady habitats appear to be more suitable for juvenile development and survival than sunny habitats. Only Parides montezuma lays most of its eggs in shady habitats, however; Battus philenor and B. polydamus females lay most of their eggs in sunny habitats. The original hypothesis is therefore not upheld by this study. Three alternative explanations for the discrepancy between the relative suitability of habitats for the juvenil...
TL;DR: Data from dimension analysis of forest biomass and production are combined with analyses of plant tissues, soil, and precipitation to describe nutrient cycling in a cool-temperate deciduous forest on a podzol.
Abstract: Data from dimension analysis of forest biomass and production are combined with analyses of plant tissues, soil, and precipitation to describe nutrient cycling in a cool-temperate deciduous forest on a podzol. Mean concentrations of nutrient elements measured (N, P, S, Ca, K, Mg, Mn, Na, Fe, Zn, Cu) in tissues are relatively low, and nutrient stocks in vegetation are low compared with other forests because of the low concentrations and the relative youth of the forest (cut in 1909-17). The largest fractions of nutrients in aboveground net primary production (NPP) go into leaves-58-78% of all nutrients except Na (45%)-although leaves are only 40% of aboveground NPP. Net community (woody) growth included -30% of aboveground NPP, but smaller fractions of nutrients (7% of N and K to 21% of Ca and 28% of Na). Nitrogen, P, and some other elements are retracted from dying leaves; but concentrations of Ca, Mn, and Na increase from living to dead leaves, branches, and stem wood. Return to the soil from aboveground is primarily by leaching for K and Na but by litterfall for other elements. "Throughflow" is defined as nutrient uptake needed beyond that in NPP to provide for both leaching and increase in dead tissues before they fall. For Na, throughflow exceeds uptake into NPP; but negative throughflows for N and P reflect conservation of these elements. Belowground plant nutrient stocks are 0.25 to 0.5 x and belowground uptake rates into NPP are 0.1 to 0.2x aboveground values for most elements, but belowground values are higher for N, P, Na, and Fe. Significant amounts of some elements, especially S, Ca, K, and Na, are exuded from roots as part of the total, above- and belowground throughflow. Behaviors of nutrient elements can be characterized by ratios expressing concentration into leaves vs. woody tissues and relative leachability and throughflow vs. conservation. Relative turnover rates compare litterfall plus leaching with aboveground stocks or with nutrient contents of NPP. Turnover rates increase in the sequence: N and P; Ca; Mg, K, Fe, and Mn; S; and Na. Means and coefficients of variation of foliage nutrient concentrations express some differences between ecosystems. Com- paring different ecosystems, coefficients of variation are low for N and P, intermediate for Ca, K, Mg, and Al, and high for Si, Mn, Fe, Cl, and Na. Differences in these and other expressions of element behavior can be interpreted on the basis of function in plants.
TL;DR: This temperate flower community, which resembles some associations of conver- gent Mullerian and Batesian mimics, appears to have evolved its characteristic convergent structure because the advantages of using similar signals and rewards to share the same hummingbird pollinators outweigh the disadvantages of diverging to reduce interspecific competition.
Abstract: We studied the pollination ecology of nine species of red, tubular flowers which bloom together in different combinations in the White Mountains of Arizona, USA. All species were strik- ingly convergent in floral color, size, and shape. Hummingbirds, the primary pollinators, usually did not visit flower species selectively, and individual birds often simultaneously carried four or more species of pollen. Flowers may have competed interspecifically for these shared pollinators, but competition was reduced because character displacement in orientation of anthers and stigma resulted in some species using different parts of the bird to transport their pollen. Most flower species secreted nectar at similar rates, particularly when they bloomed together in mixed stands. A population of Lobelia cardinalis secreted no nectar; it attracted hummingbirds by mimicing more abundant, nectar- producing species. This temperate flower community, which resembles some associations of conver- gent Mullerian and Batesian mimics, appears to have evolved its characteristic convergent structure because the advantages of using similar signals and rewards to share the same hummingbird pollinators outweigh the advantages of diverging to reduce interspecific competition.
TL;DR: Laboratory-determined larval growth rates of the detritivore (collector-gatherer) Par- atendipes albimanus (Chironomidae) responded proportionally to the microbial densities of 4 food sources as well as to the temperature and the interaction of temperature and food quality.
Abstract: Laboratory-determined larval growth rates of the detritivore (collector-gatherer) Par- atendipes albimanus (Chironomidae) responded proportionally to the microbial densities of 4 food sources. Substrates with higher microbial activities and biomasses produced greater growth rates in the order: pignut hickory (Carya glabra) leaves > white oak (Quercus alba) > insect feces > natural stream detritus. Laboratory growth rates of P. albimanus were linearly related to quantitative esti- mates of food quality based on substrate adenosine triphosphate (ATP) and respiration rates but were not statistically related to total N or C. Although P. albimanus is univoltine in Augusta Creek, Michigan, an experimental laboratory population of first-instar larvae completed a 2nd generation during the summer when fed detritus generated from hickory leaves. A second experimental popu- lation failed to develop past the first instar when fed natural detritus. The natural growth pattern of P. albimanus involves the interaction of temperature and food quality.
TL;DR: Interactions between time budgets, group size and overwinter survivorship for members of avian foraging flocks are considered and predictions relate time budgets qualitatively to both the expectation and variance of foraging group sizes.
Abstract: This paper considers interactions between time budgets, group size and overwinter survivorship for members of avian foraging flocks. Individuals should respond to the social environ- ment and energetic requirements by varying their allocation of time to predator detection, feeding and aggression. Predictions relate time budgets qualitatively to both the expectation and variance of foraging group sizes. Optimal group sizes for dominants and subordinates are compared to the ex- pected group size.
TL;DR: The energetics of four fossorial mammals, Spalacopus cyanus, Cannomys radius, Aplodontia rufa, and Scalopus aquaticus, are examined and compared to data available in the liter- ature.
Abstract: The energetics of four fossorial mammals, Spalacopus cyanus, Cannomys radius, Aplodontia rufa, and Scalopus aquaticus, are examined and compared to data available in the liter- ature. Basal rates of metabolism are lower than expected from mass if fossorial mammals weigh >80 g, but they are higher than expected if they weigh 100 g. Small burrowers may have low basal rates unrelated to burrowing habits. Minimal thermal conductances in fossorial and burrowing mammals are usually near the expected values at masses 1 kg have high minimal conductances. The temperature differential maintained at the lower limit of thermoneutrality and at temperatures above thermoneutrality is proportional to the ratio of basal rate to minimal conductance. Adaptations to a burrowing habit include (1) maintaining a small temperature differential independent of mass, which is accomplished by matching the mass sensitivity of the basal rate to that of the minimal conductance, (2) reducing basal rate, (3) increasing minimal conductance, and (4) reducing mass. The limits that exist to a reduction in mass and a reduction in basal rate of metabolism and to an increase in minimal conductance result in geographical limits to the distribution of fossorial mammals, but not necessarily to the distribution of other burrowing mammals.
TL;DR: Annual patterns in hydrology, phosphorus circulation, and sediment dynamics were studied in a southern Illinois, USA floodplain swamp dominated by bald cypress and swamp tupelo, corresponding to the rise in water level caused by beaver activity.
Abstract: Annual patterns in hydrology, phosphorus circulation, and sediment dynamics were studied in a southern Illinois, USA floodplain swamp dominated by bald cypress (Taxodium disti- chum) and swamp tupelo (Nyssa aquatica). The study emphasized the swamp's interactions with the adjacent river. For the year, major inputs of water to the swamp were throughfall (74.3 cm) and runoff (69.4 cm) with minor contributions due to groundwater (21.6 cm). Outflows were by evapo- transpiration (72.3 cm), surface outflow (56.5 cm), and groundwater (21.0 cm), with the latter two draining primarily to the river. A flood occurred during the study period, passing 1.6 x 107 m3 of river water over the swamp and depositing 0.06 cm of sediments. An annual phosphorus budget was developed for the swamp from field measurements. The greatest input of phosphorus to the swamp was 3.6 g P.m-2 yr-1, due to deposition of high-phosphorus sediments during the flood. This was 10 times greater than the outflow of phosphorus to the river, 0.34 g P.m-2 yr-', and 26 times greater than the throughfall input of 0.14 g P.m-2 yr-1. Total tree uptake from sediments was estimated to be 0.87 g P.m-2 yr-t of which 0.77 g P.m-2 yr-t returns as litterfall to the swamp sediments. Duckweed productivity was estimated to take 3.3 g P.m-2 yr-t from the water column and deposit this in the sediments during die-off. For the period 1937-1967, cypress growth, based on tree ring analyses, was closely correlated with several measures of flooding frequency and magnitude, all obtained from past river data. Tree ring data prior to 1937 showed poor correlation with flooding, probably because of logging activity. Cypress growth has decreased dramatically in recent years, corresponding to the rise in water level caused by beaver activity.
TL;DR: Differences in body size, ephippial production and habitat preferences between the 2 species are consistent with the hypothesis that planktivory is a strong selective force in their evolution.
Abstract: During 1976, midsummer reductions in densities of Daphnia pulicaria and Daphnia galeata mendotae populations occurred in Wintergreen Lake, Michigan Previous attempts to deter- mine the causes of such declines have indicated correlations between predator populations, the pres- ence of unpalatable algae or high midsummer water temperatures, and the reduction or disappearance of the daphnid populations In this study, in situ life table experiments were performed to assess the influence of natural food and temperature conditions on population growth A weekly sampling program showed that D pulicaria was dielly concentrated, after early summer, at depths between the anaerobic hypolimnion and the warmer epilimnion, consistent with previous information indicating it to be a cold-water species However, in situ life table data showed that D pulicaria was capable of surviving in epilimnetic water up to 27C, although reproduction was greatly reduced for a 6-day period in mid-July This reduction in reproduction appeared to be the result of an interaction of high temperatures, declining standing crops of small algae and increasing amounts of Anabaena, Ceratium and Volvox Daphnia galeata mendotae did not show any adverse response to these mid-July algae-temperature conditions Analysis of predator gut contents suggested that both daphnids were heavily preyed upon by bluegills (Lepomis macrochirus) Shifts in the size structure of the daphnid populations were also consistent with intense size-selective predation by bluegills, as was the tendency for the age distri- bution of parthenogenic eggs to become skewed to younger eggs as the midsummer decline proceeded Differences in body size, ephippial production and habitat preferences between the 2 species are also consistent with the hypothesis that planktivory is a strong selective force in their evolution
TL;DR: Green turtle hatching success and nest predation were investigated at Tortuguero, Costa Rica, during July-November 1977; proportionally more nests were destroyed near the end of the nesting season than during the beginning.
Abstract: Green turtle hatching success and nest predation were investigated at Tortuguero, Costa Rica, during July-November 1977. Forty-two percent of 350 study area nests and 57% of 237 beach survey nests produced emerging young; 38%. and 24%, respectively, were destroyed by dogs, coatis, and vultures. The mean emergence percentage for the successful study area nests was 83%. About 13% of all eggs deposited did not hatch. A mean incubation period of 62 d and a mean clutch size of 104 eggs were recorded. Emergence success was not influenced by other recorded parameters (nest position on beach, rainfall, turtle's tag year, time of season, incubation period, and clutch size). Incubation period was related to nest position and clutch size. Dogs, coatis, and black and turkey vultures were the chief predators at Tortuguero; dogs did the most damage. Dogs and coatis found nests at all stages of development, but destroyed more nests containing hatchlings than nests containing unhatched eggs. Predation was related to nest position, but not to nest density. Nests were destroyed in equal proportion on the entire 35.4 km of beach. Predator activity was not consistent throughout the season; proportionally more nests were destroyed near the end of the nesting season than during the beginning.
TL;DR: Three—year experiments using exclosures which excluded either ants, rodents, both taxa, or neither taxon, indicated that either taxon alone, or both taxon together, have a severe impact on the density of seeds in the soil.
Abstract: Field experiments were conducted to determine the foraging behaviors of granivorous desert ants and rodents and to ascertain the impact of these foraging efforts on the density and distribution of seeds in the soil. Foraging experiments were performed which involved providing seeds within taxon—specific enclosures in scattered and clumped distribution on the soil surface and 1.5 cm below the surface. These experiments indicated that ants only foraged on the surface, whereas rodents were able to garner seeds from below the ground. Ants foraged °85% of the experimental seed distributions on the surface and were able to retrieve °45% of the seeds they detected during any 24—h experimental run. Rodents detected 100% of all distributions and got °96% of the seeds from all distributions except scattered/belowground, from which they gathered only 75% of the seeds. Three—year experiments using exclosures which excluded either ants, rodents, both taxa, or neither taxon, indicated that either taxon alone, or both taxon together, have a severe impact on the density of seeds in the soil. When neither is present, seed densities remain high. Furthermore, any combination of granivores greatly reduces the number of samples with either high numbers of seeds or high biomass of seeds, although the ants tend to leave a greater number of large clumps of seeds than the rodents. Clumping indices are also extremely high in the absence of granivores. In opposition to the apparently detrimental effect of seed use by the granivores, surface seed—caching by rodents appears to enhance seed germination.
TL;DR: Currently used niche measures of overlap and breadth are shown to be inappropriate for analyzing field data and Comparisons of different measures of either breadth or overlap are not valid.
Abstract: Currently used niche measures of overlap and breadth are shown to be inappropriate for analyzing field data. Previously proposed measures assume resources are equally available, but this assumption is unwarranted in field studies. Comparisons of different measures of either breadth or overlap are also not valid. A measure of niche breadth is derived by asking how likely it is that a species' utilization of resources could have been drawn from the available resources in the environment. An overlap mea- sure is derived in a similar manner and represents the likelihood that the utilization of resources by one species is identical to the utilization by another species. Tests for comparing different measures are given.
TL;DR: Production of shrubs and trees, obtained from size-biomass correlations and growth measures, is compared with herb production to give an insight into the ecological balance of the savanna communities.
Abstract: Lamto savannas (Ivory Coast) are characterized by the heterogeneity of their structure and by their dynamic evolution towards forest. Life-forms and phonological cycles of herbs, shrubs, and trees reflect the constraining factors of the environment. Biomass and productivity are largely dependent on soil and climate. The specific cycles of above- and belowground biomass allow an estimate of the primary productivity. Production of shrubs and trees, obtained from size-biomass correlations and growth measures, is compared with herb production to give an insight into the ecological balance of the savanna communities.
TL;DR: The influx of large numbers of alewife, Alosa pseudoharen gus, into relatively small freshwater systems may have a considerable impact upon pre-established food chains and nutrient cycles.
Abstract: The influx of large numbers of alewife, Alosa pseudoharen gus, into relatively small freshwater systems may have a considerable impact upon pre-established food chains and nutrient cycles. We estimate the total nutrient input to Pausacaco Pond, Rhode Island, USA, from alewives amounted to 0.43 g P. 2.7 g N, and 16.8 g C/M2 over a 2-mo period. This is largely through mortality of the spawning fish, and to a lesser extent through excretion. These inputs were much greater than the eventual nutrient loss to the system through emigration of juvenile fish. In tank experiments using pond microcosms, the initial response to the addition of the fish was a large phytoplankton bloom and an increase in litter respiration. The phytoplankton bloom was short- lived, and the most lasting effect was an increase in production and respiration in the leaf litter. This increased production in the litter community would support a long lasting supply of insect and benthic invertebrate food for young fish. The respiration rate of autumn leaves incubated in alewife streams during the migration was significantly higher than that of leaves incubated simultaneously in a stream which had no alewife run. Respiration rates of leaves incubated in the same streams before the arrival of alewives did not differ significantly. The increase in litter respiration, an indication of microbial and invertebrate activity on the leaf surface, was attributed to the additional nutrients supplied by the fish.
TL;DR: It is argued that savannah P. anubis has a higher rate of exchange of individuals between groups than has been recorded for the rain forest primates under consideration, and the differing rates of exchange are due to disease-related selection against traits which result in high rates of individual exchange among rain forest primate groups.
Abstract: The intestinal protozoan faunas of 11 social groups of Cercocebus albigena, 3 groups of Cercopithecus mitis, 3 groups of Cercopithecus ascanius, 2 groups of rain forest and 4 groups of savannah Papio anubis are documented. All individuals in a particular social group exhibit identical protozoan faunas. All social groups of each species, except the savannah P. anubis, exhibit intergroup differences in the composition of their protozoan faunas. The number of intestinal, protozoan species in Cercocebus albigena social groups is a function of group size. The similarity between the protozoan faunas of different C. albigena groups is related to the density of social groups and types of land tenure in particular localities. Past social history of C. albigena groups may have some influence on the level of similarity of different groups' faunas. Entrance of a nongroup member into a group of Cercopithecus mitis resulted in an increase in the species richness of the group's protozoan fauna. Group fission may result in reduction of a group's protozoan species richness. All groups of savannah Papio anubis exhibit identical protozoan faunas. I argue that this is because savannah P. anubis has a higher rate of exchange of individuals between groups than has been recorded for the rain forest primates under consideration. I hypothesize that the differing rates of exchange are due to disease-related selection against traits which result in high rates of individual exchange among rain forest primate groups. Primate social groups are functionally biological islands; the species richness of their protozoan faunas changes according to group size and levels of protozoan migration between groups.