ISSN:0012-9658    

DOI:10.2307/1940004

出版商:Ecological Society of America    

年代:1992

数据来源: WILEY

摘要:

Predator—prey theory is traced from its origins in the Malthus—Verhulst logistic equations, through the Lotka—Volterra equations, logistic modifications to both prey and predator equations, incorporation of the Michaelis—Menten—Holling functional response into the predator and prey equations, and the recent development of ratio—dependent functional responses and per—capita rate of change functions. Some of the problems of classical predator–prey theory, including the paradoxes of enrichment and biological control, seem to have been caused by the application of the principle of mass action to predator–prey interactions. Predator–prey models that evolved from logistic theory or that incorporate ratio—dependent functional responses do not have these problems and also seem to be more biologically plausible.

ISSN:0012-9658    

DOI:10.2307/1940005

出版商:Ecological Society of America    

年代:1992

数据来源: WILEY

摘要:

Ratio—dependent and prey—dependent models of trophic interactions make very different predictions about the steady—state (equilibrial) properties of ecosystems, such as the response of equilibrium abundance and biomass of organisms in each trophic level to increased primary productivity or nutrient input. Prey—dependent theory predicts alternating positive, negative, and zero responses of trophic levels to increased productivity, whereas ratio—dependent theory predicts proportional increase in all trophic level biomasses. We analyzed data on the nutrient input and the biomasses of phytoplankton, zooplankton, and fish across lakes to distinguish between ratio—dependent and prey—dependent models. The results show parallel increases in all trophic levels as a result of increased nutrient input, demonstrating that natural systems are closer to ratio dependence than to prey dependence.

ISSN:0012-9658    

DOI:10.2307/1940006

出版商:Ecological Society of America    

年代:1992

数据来源: WILEY

摘要:

Classical models describing the number of prey consumed by predators rest on an analogy with the law of mass action and, consequently, the functional response of predators depends only on the density of prey. An alternative model is that the functional response depends on the ratio of prey and predator densities. We hypothesize that the applicability of one or the other model depends on the degree of heterogeneity of predators and prey in space, the prey—dependent model being appropriate in homogeneous situations while the ratio—dependent model is appropriate in heterogeneous situations. We have designed experiments to test this hypothesis, using cladocerans filter—feeding on algae. The design is such that the two types of dependence can be discriminated by observation of equilibrium patterns. Daphnia magna and Simocephalus vetulus, the two cladoceran species tested, differ in their spatial distributions. Daphnia has homogeneous distribution whereas Simocephalus has heterogeneous distribution. Experimental results support the hypothesis: D. magna follows the prey—dependent model and S. vetulus follows the ratio—dependent model. By artificially modifying the environment of the two species, we forced D. magna to a heterogeneous distribution and S. vetulus to a homogeneous distribution. As a consequence, each species changed its dependence, further confirming our hypothesis.

ISSN:0012-9658    

DOI:10.2307/1940007

出版商:Ecological Society of America    

年代:1992

数据来源: WILEY

摘要:

Ratio—dependent models of predators and prey are approximations of the biology of resource acquisition and allocation and their consequences for population birth and death rates. A demand—driven functional response model that has a physiological basis in mass (energy) dynamics is reviewed (i.e., the metabolic pool model), and its obvious links to the logistic model are outlined. To demonstrate the utility of this approach, a distributed maturation time age—structure model of the dynamics of A. J. Nicholson's classic laboratory population data on the sheep blow fly (Lucilia cuprina Weidman) is developed. The model provides sufficient information on the dynamics of the intermediate life stages to show that the blow fly oscillations were due to the effects of larval competition for food on size, fecundity, and pupation success. These results agree with Nicholson's conclusions. The advantage of this model, in contrast to prior models, is that the dynamics emerge by considering the processes of resource acquisition and allocation as they affect growth, reproduction, and survival. No explicit time delays, which automatically lead to oscillations, were included. Lastly, the notions of the metabolic pool model are found in Nicholson's original model for equilibrium population density. The metabolic pool paradigm in an age—structure setting is used to model the tri—trophic dynamics of Acyrthosiphon aphids in an alfalfa ecosystem. The model explains the role of the various natural enemies in the regulation of the aphids.

ISSN:0012-9658    

DOI:10.2307/1940008

出版商:Ecological Society of America    

年代:1992

数据来源: WILEY

ISSN:0012-9658    

DOI:10.2307/1940009

出版商:Ecological Society of America    

年代:1992

数据来源: WILEY

摘要:

Most theoretical models of the evolution of conditional responses require some form of cost to balance the benefits of an intermittently deployed character. The inducible spines, keels, and helmets of marine and freshwater invertebrates have proven to be tractable subjects for testing this hypothesis. Membranipora membranacea, a marine bryopzoan, produces large spines within 2 d of detecting chemical cues from a predatory mollusc. The spine response, which increases with the level of predator attack and varies with colony size, is associated with reduced growth of colonies in short—term laboratory experiments. Because of the plastic nature of allocation shifts in colonial invertebrates, lifetime fitness consequences for inducibly defended colonies in the field were measured in this study. In two successive years, spined colonies grew somewhat more slowly, but also reproduced sooner than less—spined colonies. Spined colonies also senesced sooner than unspined colonies in the one year measured. The differences in growth trajectories between spined and less—spined colonies detected in the field were small relative to those predicted from short—term laboratory experiments, emphasizing the importance of field studies to evaluate the costs of defense in nature.

ISSN:0012-9658    

DOI:10.2307/1940010

出版商:Ecological Society of America    

年代:1992

数据来源: WILEY

摘要:

The distance over which propagules can successfully colonize new sites depends on processes that increase the time they remain competent while being dispersed. As do feeding larvae, algal spores can contribute to their own nutrition (via photosynthesis) during dispersal. We explored the dispersal potential of the kelps Macrocystis pyrifera and Pterygophora californica in laboratory experiments by examining (1) how long their spores can swim, (2) the contribution of energy derived from photosynthesis to spore swimming duration, and (3) the ability of spores to germinate and attach after they stop swimming. Results indicate that under photosynthetically saturating irradiance no spores of either species can swim longer than 120 h;<10% of the spores were still swimming after 72 h. When placed in the dark, spores did not swim longer than 72 h;<10% remained swimming after 48 h. More importantly, spores did not die after they stopped swimming; most germinated in the water column and retained their capacity to produce viable sporophyte recruits. The ability of spores to attach after they stopped swimming differed between the two species; settlement density declined in Macrocystis and increased in Pterygophora. Thus, the viable planktonic stage of these algae is not necessarily restricted to the spore but may include later life history stages. These results provide biological evidence that the spores and germlings of these kelps can remain competent in the plankton for extended periods of time, which is consistent with our previous findings that their dispersal can occur over greater distances than previously thought possible.

ISSN:0012-9658    

DOI:10.2307/1940011

出版商:Ecological Society of America    

年代:1992

数据来源: WILEY

摘要:

Reproductive investment of the intertidal kelp Alaria nana was manipulated experimentally to investigate costs of reproduction. Allocation patterns were examined using treatments that employed vegetative and reproductive tissue removal. Growth, survivorship, size, reproductive investment, carbon, nitrogen, and phenolic secondary metabolities were monitored in tagged experimental plants. Further experiments investigated the contribution of reproductive tissue to drag forces on the plant in intertidal environments. Carbon, nitrogen, and phenolics were all higher in reproductive tissue (sporophylls) compared to vegetative tissue (the frond) in control plants. When some vegetative tissue was removed, carbon and nitrogen in the sporophylls decreased while percent phenolics remained unchanged. Reproductive tissue removal had no effect on plant survirorship, growth, or size compared with control plants. When the entire frond was kept clipped, sporophyll number decreased, often to the point of complete attrition. Although allocation patterns in Alaria nana are consistent with reproductive costs (i.e., the sporophylls are not self—supporting), there is no evidence that reproduction imposes costs on the plant that are demographically important such as growth, size, and survivorship. Instead, both reproductive investment and percent phenolics were positively correlated with growth and size in control plants.

ISSN:0012-9658    

DOI:10.2307/1940012

出版商:Ecological Society of America    

年代:1992

数据来源: WILEY

摘要:

The sea urchin Diadema antillarum increases the relative size of Aristotle's lantern (length of demipyramid) when food limited. This provides a tool for investigating algal abundance and biotic interactions in the past. A field collection of D. antillarum provided a baseline relationship between demipyramid length and body size (test diameter). Experimental manipulations of food availability and population density resulted in shifts in relative demipyramid length. The baseline and experimental data provide a range of responses that was compared to museum specimens collected over the past 100 yr from 30 locations in the Caribbean. The relative demipyramid lengths from the museum specimens were also compared over time, and with human population density, human fishing pressure, and geographic region. The results indicate that relative demipyramid size is indirectly influenced by human activity and varies with geographic region. This suggests that human fishing pressure has influenced Caribbean coral reef community structure by affecting predator—herbivore relationships. However, this human impact may be small relative to naturally occurring variation in demipyramid size.

ISSN:0012-9658    

DOI:10.2307/1940013

出版商:Ecological Society of America    

年代:1992

数据来源: WILEY