摘要:

We compared principal components derived from sets of real data with dimensions of 120 x 7, 120 x 4, 150 x 11, 150 x 8, 150 x 5, 454 x 12, 454 x 8, and 454 x 5, to those from sets of randomly generated data of corresponding size. Principal components from subsets of 25, 50, 75, and 100 observations from the 120— and 150—observation data sets and those from subsets of 25, 50, 75, 100, 150, 200, 300, and 400 observations from the 454—observation data sets were compared. Percent variance association with components from real data was relatively constant over all sample sizes; percent variance decreased with larger samples of random data. A bootstrap method was used to develop standard error estimates on percent variance and percent of remaining variance associated with components from real data. Percent of remaining variance associated with the first four components from real data was significantly higher than analogous components from random data.

ISSN:0012-9658    

DOI:10.2307/2937364

出版商:Ecological Society of America    

年代:1985

数据来源: WILEY

摘要:

Preferential orientation, pursuit, and capture by a predator have been proposed for the establishment of prey preference and prey switching; however, very little is known about which of these behaviors is actually involved in active prey selection. Based on laboratory arena experiments in which the proportions of two prey types were manipulated, I distinguished the specific foraging process underlying prey preference and prey switching in nymphs of the dragonfly Anax junius. Dragonfly nymphs showed a higher probability of pursuing the more abundant of two prey types than predicted from relative prey frequencies. An increase pursuit probability was correlated with an increased capture success on the abundant prey type. I hypothesize that prey selection in Anax junius nymphs results from a simple behavioral rule of thumb;Continue to pursue only those prey types you have successfully captured in the immediate past."

ISSN:0012-9658    

DOI:10.2307/2937365

出版商:Ecological Society of America    

年代:1985

数据来源: WILEY

摘要:

The aquatic larvae of the salamanders Ambystoma maculatum and A. opacum (Ambystomatidae) co—occur in temporary ponds. Both species are generalized predators and, as previously reported, the size ratio of the two as larvae makes A. maculatum vulnerable as prey to A. Opacum. Earlier results suggested that predation by A. opacum can be a major contributor to A. maculatum mortality. To determine the extent of natural variation in the relative size and density of the two species, and to investigate the possible relationship between predator and prey larval densities in the field, egg and larval densities of both species were monitored in 13 natural ponds during two years. The effects of alternative prey (anuran tadpoles) and prey refuges (leaves or pondweed) on the number of prey surviving were also studied in laboratory aquaria. It was determined that several factors may modify the rate of predation on A. maculatum by A. opacum larvae. Although many of the ponds surveyed had high densities of A. opacum, others had none or low densities. An apparent negative association between prey density and predator density in four ponds was found. The growth rate of A. opacum larvae was shown to be the density—dependent, so the size of the predators to which A. maculatum hatchlings are exposed varies. In laboratory experiments the presence of alternative prey for A. opacum, and ofphysical refuge for A. maculatum, improved A. maculatum survival. Since the presence of alternative prey and refuge was found to vary among ponds, these factors could contribute to variation in the rate of predation by A. opacum in nature. It was concluded that interpond and interyear differences may be important in the ability of A. opacum.

ISSN:0012-9658    

DOI:10.2307/2937366

出版商:Ecological Society of America    

年代:1985

数据来源: WILEY

摘要:

Behavioral experiments were carried out in flow—through observation boxes in New York and Colorado streams to determine whether interactions between pairs of predaceous stoneflies were characterized by exploitative or interference competition and to determine the effect of prey density on such interactions. The presence of a competitor generally reduced the number of attacks and the time that predaceous stoneflies spent eating mayflies (Baetidae). Coexisting perlids (Acroneuria carolinensis and Agnetina capitata) in the New York stream and perlodids (Megarcys signata and Kogotus modestus) in the Colorado stream had mutual negative effects on each other's foraging behavior despite significant size differences between species (first larger athan second). A larger omnivorous stonefly (Pteronarcella badia, Pteronarcydae) also suppressed the feeding behavior of Megarcys, but a reciporcal effect was not observed. Most competitive encountes resulted in submissive or evasive behavior by one or both stoneflies ultimately leading to avoidance of further contact. Some stoneflies, however, were occassionally aggressive, either toward consecifics (Kogotus) or toward a smaller species or predator (Megarcys toward Kogotus). This behavior is consistent with the hypothesis that interference is a mechanism of competition among these stoneflies. The frequency of aggressive interactions increased for all stoneflies when prey density increased from 0 to 15 individuals per box but declined at 30 prey individuals per box. This observation suggests that the level of aggression is variable with availability of a food resource. As prey density increased, behavior associated wth predator—prey interactions (attacks, feeding) increased for some stoneflies, and other activities (dispersal, cleaning, stationary behavior) decreased, generally increasing the predator's probability of finding and consuming prey. Large species of stoneflies had shorter prey handling times than small species, and all stoneflies had very low rates of capture (successful captures 10—25% of total attacks. We postulate that direct interference competition from other stoneflies and predator—mediated dispersal of prey (unstable prey patches) reduce the benefit of aggregating in regions of high prey density.

ISSN:0012-9658    

DOI:10.2307/2937367

出版商:Ecological Society of America    

年代:1985

数据来源: WILEY

摘要:

Planktivorous bluegill sunfish (Lepomis macrochirus) are known to consume large prey preferentially. Disagreement exists in the literature over whether this size—selectivity reflects optimal foraging behavior by the fish or relative prey encounter probability as predicted by a model in which apparent size of the prey determines foraging preferences. As bluegills grow larger, their visual resolution increases, and this should affect prey choice under the apparent size model. In laboratory experiments, three sizes or fish were fed identical diets made up of three sizes of Daphnia magna. Large and medium—size fish consumed relatively more large prey than predicted by the apparent size model, whereas the diet of small fish deviated only sightly from the apparent size model. For fish to be more selective than allowed by the apparent size model, they must be able to estimate absolute prey size. To do this requires good vision. Since diet selectivity was highly significantly correlated with the fishes' visual resolution in our experiments, we suggest that visual capability imposes a constraint on the ability of small bluegills to choose prey.

ISSN:0012-9658    

DOI:10.2307/2937368

出版商:Ecological Society of America    

年代:1985

数据来源: WILEY

摘要:

Two abundant, widely co—occurring aphid species exposed to natural or reduced predation of goldenrod transplanted as either solitary stems or small, discrete patches of plants. Local interplant movement increased colonization rates for both species, resulting in more larger aphid colonies on patch plants than on solitary plants. Predator reduction increased aphid densities and produced evidence of increased resource limitation and interspecific competition, although the specific response differed between plant spacing treatments. On solitary plants, predator reduction resulted in a significant negative spatial association between the aphid species. Predator reduction in patches resulted in an increase in one species but a reduction in colony size of the other. In all cases, aphid abundance was negatively associated with plant health. Patterns of spatial association between the aphid species varied with experimental treatments. Aphids on solitary plants at reduced predation, aphids on patch plants showed no overall patterns of association. With natural predation, aphids on patch plants were positively associated, as were aphids within natural goldenrod patches in the field. The results show that predation and local interplant movement determine patterns of spatial overlap and mediate and impact of interspecific competition. Although resource limitation can influence aphid dynamics on a single goldenrod shoot, predation and interplant movements are considered to have a greater influence on community structure at a large spatial scale. These results are discussed in terms of several recent models of predator—mediated coexistence of a subdivided resource.

ISSN:0012-9658    

DOI:10.2307/2937369

出版商:Ecological Society of America    

年代:1985

数据来源: WILEY

摘要:

Manly's measure of selectivity is a particularly useful measure of resource selectivity by resource users because it is often simply related to biologically meaningful parameters in resource use models. This papers describes how Manly's measure is naturally suited for log—linear model analysis. If resources users can be cross—classified by factors such as age and sex, log—linear models provides a convenient method for examining how selectivities depend on these factors. The techniques are applicable when resource usages occur independently and do not affect the resource availabilities.

ISSN:0012-9658    

DOI:10.2307/2937370

出版商:Ecological Society of America    

年代:1985

数据来源: WILEY

摘要:

Laboratory experiments were conducted with the periphyton—grazing mayfly Baetis tricaudatus to test the hypothesis that stream drift results from the passive removal of individuals from substrates. This hypothesis accounts for entry into the water column and diel drift periodicities, based on changes in the positioning of individuals on substrates and changes in their activity rates. A factorial design that incorporated food abundance (low or high), food distribution (low, intermediate, or high degree of patchiness), and forager hunger level (starved or well fed) was used to produce contrasting diel behavioral patterns necessary to test the hypothesis. Nymph behavior was monitored during the day and night using time—lapse cinematography and direct visual observations. Nymphs fed ad libitum had greater proportions of individuals on top surfaces at night that during the day. Starved nymphs showed little day—night variation in activity or positioning behavior, and their behavior during the day was similar to that of fed nymphs at night. Therefore, if drift—entry was passive, diurnal drift of starved nymphs should have been greater than or equal to nocturnal drift of fed nymphs in comparisons made within food levels. In all cases this prediction was not supported. These results refute the passive drift—entry hypothesis and support the alternative hypothesis of active entry into the water column. Drift patterns and foraging behaviors in these experiments and in an additional set of experiments were analyzed to identify proximate factors responsible for active drift—entry by Baetis. Drift was greatest at night and at the low food level. Periphyton patchiness and nymph hunger level did not significantly affect drift in the factorial experiments. In additional experiments, over a wide range of food abundance (2.5 x 105to 107diatom cells/cm2), the proportion drifting at night was significantly greater than zero when food was patchily distributed on substrates, but not when food was uniformly distributed. Based on these results and behavioral observations suggesting that food patches were less readily encountered with increasin degree of patchiness, I suggest that active drift is a component of Baetis food searching behavior and that individuals abandon habitats by enterin the water column when their estimate of habitat quality falls to some threshold level.

ISSN:0012-9658    

DOI:10.2307/2937371

出版商:Ecological Society of America    

年代:1985

数据来源: WILEY

摘要:

We constructed a patch dynamics model which can be used to simulate the changing sizes of resident populations in a series of interconnected habitat patches. We applied the model to white—footed mice (Peromyscus Leucopus) inhabiting patches of forest in an agricultural landscape. The model predicts that mouse populations in isolated woodlots have lower growth rates and are thus more prone to extinction than those in connected woodlots. Field data support this prediction.

ISSN:0012-9658    

DOI:10.2307/2937372

出版商:Ecological Society of America    

年代:1985

数据来源: WILEY

摘要:

Previous studies on the Texas coastal prairie implicated habitat as the primary factor producing variation in demography and resource use of the cotton rat (Sigmodon hispidus). In this community, secondary succession has resulted in a patchy distribution of habitat types. Hence, dietary responses, individual occurrence, and the process of habitat selection were investigated to elucidate interactions with habitat. Diet measurements for animals constrained to known habitats in each season revealed little variation in diet relative to variation in resource availability. This pattern was maintained by dynamic shifts in resource selectivity. Grasses were most frequent in the diet, forbs were maintained at low levels, and berries were consumed opportunistically. Results of a 2—yr livetrapping census showed that individual cotton rats were nonrandomly distributed on the livetrapping grid. They were positively associated with habitat dominated by monocots and exhibited density—dependent occurrence in dicot and mixed habitat types. Overall, females were more specific to monocot habitat than males, but when lactating they occurred most frequently in mixed habitat, possibly to facilitate acquisition of a balance diet. Habitat selection was analyzed as a simple Markov chain or which transition probabilities were estimated from capture—recapture data. Transition matrices were stationary with respect to density and sex, but not age. Adults were most likely to select a monocot habitat, subadults selected both mixed and monocot habitats, and juveniles were least selective. Behavioral interactions were suggested to account for these age effects.

ISSN:0012-9658    

DOI:10.2307/2937373

出版商:Ecological Society of America    

年代:1985

数据来源: WILEY