Ecology
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Some Effects of Temperature and Oxygen Concentration on Phyllopod Ecology Seasonal distributional patterns of five phyllopods from southwest Texas are similar to those of the same species from more northern latitudes. At both latitudes a primary environmental cue controlling the appearance of phyllopods seems to be temperature. For instance, in Texas Branchinecta packardi was the only cold water species. In addition to the effects of temperature on phyllopod zoogeography, diurnal studies show that high temperatures contribute both directly and indirectly to oxygen depletion in temporary ponds. The comparative tolerance of phyllopods to near anaerobic conditions was as follows: calm shrimp, Caenestheriella setosa > tadpole shrimp, Triops longicaudatus > fairy shrimp, Streptocephalus texanus.
Ecology - Tập 52 Số 2 - Trang 343-347 - 1971
Some Notes on Estimating the Competition Matrix, a Recent theoretical and field work on communities of interacting species has employed various forms for estimating the competition matrix elements, αi j , from utilization coefficients pi a (which measure the relative utilization of the path resource category by the ith species). Some little—known properties of these forms are discussed. When more than one resource dimension is involved, there is in general no substitute for measuring the species' full multidimensional utilization functions; a critical discussion is given of the estimation of such multidimensional competition coefficient αi j by products of one—dimensional coefficients.
Ecology - Tập 56 Số 3 - Trang 737-741 - 1975
On the Measurement of Niche Breadth and Overlap Measures of niche breadth and overlap that depend on the distribution of individual among resource states (ecological categories) should be independent of the relative abundance of the species and of the number of resource states considered. Such measures should also take into account the degree of distinctness of the resource states from the point of view of the organisms concerned. An ecoassay of the distinctness of resource states may well be easier and more meaningful than measurements of physical and chemical factors. We propose that the species composition of communities utilizing different resource states may be used to develop weighting factors with which each state may be weighted in proportion to its degree of distinctness. The weighting factors are used in the development of indices of niche breadth and overlap that correct for variation in the range and distinctness of resource states and that suffer less from human subjectivity than do the measures used to date. The use of such indices and the relationship of niche overlap to competition are discussed.
Ecology - Tập 52 Số 4 - Trang 567-576 - 1971
COEXISTENCE OF THE NICHE AND NEUTRAL PERSPECTIVES IN COMMUNITY ECOLOGY
Ecology - Tập 87 Số 6 - Trang 1399-1410 - 2006
EFFECTS OF HABITAT COMPLEXITY AND COMPOSITION ON A DIVERSE LITTER MICROARTHROPOD ASSEMBLAGE
Ecology - Tập 81 Số 4 - Trang 1120-1132 - 2000
The Vegetational Structure of an Abandoned Field in Southeastern Michigan and Its Relation to Environmental Factors
Ecology - Tập 36 Số 4 - Trang 685-706 - 1955
Fire Intensity Effects on Germination of Shrubs and Herbs in Southern California Chaparral The study reported here investigates the effects of fire intensity and combustion products (ash and char) on shrub and herbaceous seedling emergence in the field in a mixed southern California chaparral, which was dominated by a facultative seeder, Adenostoma fasciculatum, and by an obligate seeder, Ceanothus greggii. Fire effects were studied in two winter burns, one of which as manipulated by adding brush to experimental plots to increase fire intensity. Adenostoma was very sensitive to increasing fire intensity, with decreasing seedling production as fire intensity increased. This was detected within the normal range of fire intensities of a winter burn, and to a greater extent when intensities were experimentally modified. Ceanothus germination was either stimulated by, or very resistant to, increasing fire intensity. Increasing fire intensity also promoted earlier germination of Ceanothus. Herb species were also differentially affected by increasing fire intensities. Among the abundant herbs, fire annuals like Phacelia brachyloba were more resistant to increasing fire intensity than opportunistic annuals like Cryptantha muricata. Seedling production of one opportunistic annual, Lotus strigosus, was however, stimulated by all levels of increased fire intensity. In most cases, ash and char did not affect field germination. Fire intensity can profoundly modify seedling production of shrubs and herbs after a fire. By substantially altering post—fire seedling populations, fire intensity may represent a major factor in controlling species composition and diversity in chaparral.
Ecology - Tập 72 Số 6 - Trang 1993-2004 - 1991
Can We Use Experiments and Models in Predicting the Invasiveness of Genetically Engineered Organisms?
Ecology - Tập 77 Số 6 - Trang 1670-1675 - 1996
OPTICAL CHARACTERISTICS OF NATURAL WATERS PROTECT AMPHIBIANS FROM UV-B IN THE U.S. PACIFIC NORTHWEST
Ecology - Tập 83 Số 11 - Trang 2951-2957 - 2002
Arthropod Community Responses to Manipulation of a Bitrophic Predator Guild We used replicated field enclosures to manipulate population densities of two species of bitrophic predators in a terrestrial old—field community: a mantid (Tenodera sinensis), and a wolf spider (Lycosa rabida). The treatments consisted of adding mantids alone (8 individuals/enclosure), lycosids alone (10 individuals/enclosure), and lycosids and mantids together (8 + 10 individuals). A control consisted of enclosures to which no predators were added. The impact of these predators on numbers and biomass of other arthropods in the community was examined on several levels: overall community, different size (body length) categories, and major taxa. We asked whether the impact of these predators in combination could be predicted from their separate effects. Mantids depressed total numbers (10—15%) and biomass (50%), in the arthropod community over the course of 10 d. This effect was confined to the largest size categories in the community. Lycosids had no measurable effect at this level of resolution. Mantids depressed abundance of acridids in both mantid and mantid/lycosid enclosures, but again lycosids had no impact. Lycosids alone enhanced abundance of gryllids, but not in the presence of mantids. Both mantids and lycosids depressed numbers of small spiders (also members of this guild), but this effect was not additive. Interactions among members of bitrophic generalist predator guilds may contribute to the commonness of nonadditive and higher order effects in manipulative experiments. Depending upon the level of resolution, it may be impractical to predict the impact of the whole guild from summing the individual effects of single predator species on terrestrial arthropod communities.
Ecology - Tập 71 Số 6 - Trang 2107-2114 - 1990
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