ISSN:0012-9658    

DOI:10.2307/2265528

出版商:Ecological Society of America    

年代:1996

数据来源: WILEY

摘要:

The addition or deletion of a species from a community is likely to have effects on the trait values of other species and on their population densities. This article argues that current theory is insufficiently developed to provide guidance in predicting what might happen to either traits or population densities. In addition, there has been relatively little empirical work to examine many of the phenomena that have been predicted by the limited available theory. The example of character displacement of competitors is reviewed to reveal some of the gaps in our knowledge about the evolutionary consequences of additions or deletions. The example of evolution of traits related to predation in food webs is used to reveal gaps in our knowledge of the population—level consequences of evolutionary changes initiated by a species addition or deletion. Several approaches to studying combined evolutionary and ecological processes in multispecies communities are discussed. Some previous multispecies models have been too abstract to be easily related to more mechanistic two—species models, but recent methods derived from quantitative genetics may result in significant advances in understanding multispecies systems and their relationship to communities with fewer species.

ISSN:0012-9658    

DOI:10.2307/2265529

出版商:Ecological Society of America    

年代:1996

数据来源: WILEY

摘要:

Indirect effects occurring through chains of direct species interactions have been shown to be important in many communities. If indirect effects have strong ecological effects, then they must also have strong evolutionary effects through natural selection. We consider how indirect effects, both positive and negative, combine with positive and negative direct effects to influence evolution between interacting species. Any one species can evolve in response to direct interactions with other species by changing its “response” to the presence of the other species or changing its “effect” on the species. We argue that the direction (positive or negative) of the direct and indirect effects will determine whether traits related to “response” or “effect” are most likely to be subject to natural selection. Further, covariance patterns of species in the same community should increase when direct and indirect effects between species act in the same direction, resulting in greater compartmentalization of such communities.

ISSN:0012-9658    

DOI:10.2307/2265530

出版商:Ecological Society of America    

年代:1996

数据来源: WILEY

摘要:

Researchers have been using simple morphological measures as indicators of ecological features for some time. The utility of morphological variables as ecological indicators depends upon our understanding of how the variable effects the ability of the organism to perform a particular task. Functional morphological analyses identify those features that can be directly related to behavioral performance and help to distinguish causal functional relationships from spurious correlations. The behavioral abilities of the individual, in turn, shape patterns of resource use and fitness by placing limits on the range of resources that can be utilized and by shaping the cost/benefit curve for resource choices. Examples from research on the feeding biology of North American sunfishes are discussed to illustrate how functional morphology can be used to provide explanations for differences between species in patterns of prey use, patterns of habitat use, ontogenetic diet switches, and population size. Trends from analyses of the evolution of fish feeding mechanisms suggest specific functional features that are most likely to vary among taxa and underlie differences in feeding performance and diet. Included in this group of predictive variables are the organization of lever arms in the jaw opening and closing systems, the size of the mouth, and the size of muscles used in prey—crushing behaviors. The link between morphology and ecology will be made most firmly when variables are chosen that clearly reflect the ability of the organism to perform relevant behaviors.

ISSN:0012-9658    

DOI:10.2307/2265531

出版商:Ecological Society of America    

年代:1996

数据来源: WILEY

摘要:

Ecologists have long been interested in the differences that exist among communities. If species adapted rapidly and without constraint, and if any lineage could occur in any community, then we would expect differences in community structure to be indicative of environmental differences. Because lineages differ in their evolutionary potential and are geographically restricted, however, comparisons of community structure must take account of communities' histories. Phylogenetic information about the constituent lineages in a community can allow lineage effects to be factored out, thus allowing an assessment of environmental determinants of community structure. In addition, phylogenetic information permits understanding of how communities have evolved through time and suggests hypotheses that may be tested using extant communities. Methodological difficulties with the application of these methods to community ecological issues are also discussed.

ISSN:0012-9658    

DOI:10.2307/2265532

出版商:Ecological Society of America    

年代:1996

数据来源: WILEY

摘要:

Regional species diversity limits the diversity of local communities by defining the pool of species that are available to colonize sites. Biogeographical processes that influence speciation and extinction rates determine the size and composition of this regional species pool. Community ecologists are beginning to recognize the importance of these biogeographical processes in influencing diversity patterns among local communities, but the potential for local interactions to influence biogeographical processes, especially speciation, has been little considered. In this paper I discuss one mechanism by which variation in the strengths of local interactions can influence the potential for population differentiation and thus for influencing speciation rates in the allopatric model of speciation. When more than one selective agent acts on the phenotype, the shape of the overall fitness surface depends critically on the relative strengths of the various selective agents. If one selective agent, which imparts strong selection, acts in all populations of a species, population differentiation via adaptation to local ecological conditions or via differentiation of sexual systems is retarded because the overall fitness surface in all populations strongly resembles the shape of the strongest selective agent. Consequently, the potential for speciation is reduced. Alternatively, if selective agents in various populations impart relatively equitable strengths of selection, the potential for differences in the overall fitness surfaces among populations is enhanced, which will enhance the potential for population differentiation and thus speciation. Analogous results obtain when multiple selective agents impact genetically correlated characters. Because the strength of selection generated by a species interaction should increase with the strength of the interaction, and because fewer species can usually coexist when the strengths of interactions are greater, the number of coexisting species and the potential for speciation in component taxa may covary among communities. This analysis indicates that the relative strengths of interactions can be as important to diversification in communities as the number of niche dimensions along which differentiation can occur.

ISSN:0012-9658    

DOI:10.2307/2265533

出版商:Ecological Society of America    

年代:1996

数据来源: WILEY

摘要:

The fossil record provides a wealth of data on the role of regional processes and historical events in shaping biological communities over a variety of time scales. The Quaternary record with its evidence of repeated climatic change shows that both terrestrial and marine species shifted independently rather than as cohesive assemblages over scales of thousands of years. Larger scale patterns also show a strong individualistic component to taxon dynamics; assemblage stability, when it occurs, is difficult to separate from shared responses to low rates of environmental change. Nevertheless, the fossil record does suggest that some biotic interactions influence large—scale ecological and evolutionary patterns, albeit in more diffuse and protracted fashions than those generally studied by community ecologists. These include: (1) the resistance by incumbents to the establishment of new or invading taxa, with episodes of explosive diversification often appearing contingent on the removal of incumbents at extinction events; (2) steady states of within—habitat and global diversity at longer time scales (107—108yr), despite enormous turnover of taxa; and (3) morphological and biogeographic responses to increased intensities of predation and substratum disturbance over similarly long time scales. The behavior of species and communities over the array of temporal and spatial scales in the fossil record takes on additional significance for framing conservation strategies, and for understanding recovery of species, lineages, and communities from environmental changes.

ISSN:0012-9658    

DOI:10.2307/2265534

出版商:Ecological Society of America    

年代:1996

数据来源: WILEY

摘要:

Numerous insects, including Drosophila nigrospiracula, that inhabit necrotic cacti of the Sonoran desert are host to Macrocheles subbadius, a cosmopolitan mesostigmatid mite. This paper shows that the mite pierces Drosophila integument and ingests haemolymph while attached to the abdomen of its host. Among field—caught flies, there was a strong negative relationship between mite load and wet mass of adult flies of both sexes. Thus, M. subbadius is an ectoparasite of D. nigrospiracula, contrary to the widespread belief that macrochelids form only phoretic associations with adult flies. The parasite harms its host in many ways. Under laboratory conditions, there was a significant negative effect of mite load on survivorship. In the field, there was a significant negative relationship between mite load and number of eggs carried by sexually mature females, suggesting that infested females resorb their oocytes to compensate for nutritional stress imposed by feeding mites. Likewise, in the laboratory, infestation lengthened somewhat the period prior to onset of oviposition, and decreased the number of eggs laid by females over their life. However, mite—infested females maintained on a yeast—supplemented diet overcame the potentially debilitating effects of mites, and were actually slightly, but not significantly, more fertile than uninfested females. Since the dietary conditions of flies influenced the degree to which fecundity was affected, the debilitating effect of mites is comparable to that of starvation. This conclusion derives support from the observation that laboratory females infested for 4 d, but whose mites were subsequently removed, produced fewer progeny than uninfested females. Although this effect was significant only among old females, it nevertheless indicates that the observed effects of mites on fecundity are not the result of mechanical constraints on oviposition behavior. Since intensities of infestation used in laboratory experiments were similar to those encountered in nature, observed ectoparasitic effects on fly fitness suggest that M. subbadius can reduce fly numbers in nature.

ISSN:0012-9658    

DOI:10.2307/2265535

出版商:Ecological Society of America    

年代:1996

数据来源: WILEY

摘要:

Parasites that are transmitted from prey to predator are often associated with altered prey behavior. Although many concur that behavior modification is a parasite strategy that facilitates transmission by making parasitized prey easier for predators to capture, there is little evidence from field experiments. We observed that conspicuous behaviors exhibited by killfish (Fundulus parvipinnis) were associated with parasitism by larval trematodes. A field experiment indicated that parasitized fish were substantially more susceptible to predation by final host birds. These results support the behavior—modification hypothesis and emphasize the importance of parasites for predator—prey interactions.

ISSN:0012-9658    

DOI:10.2307/2265536

出版商:Ecological Society of America    

年代:1996

数据来源: WILEY

摘要:

While the role of parasites in shaping population and community dynamics has been increasingly appreciated, researchers have largely ignored the ecology of parasitic plants. Parasitic plants obtain water, sugar, nitrogen compounds, and a variety of secondary metabolites from their host plants. In a greenhouse study, I examined the direct interactions of a parasitic plant, Castilleja wightii (Scrophulariaceae), with three plant hosts and the indirect effects of this parasitism on the performance of a parasite—feeding herbivore. The three host species, Lupinus arboreus, Artemisia pycnocephala, and Eriophyllum staechadifolium, directly and differentially affected C. wightii flower production, although parasite biomass was not affected by host species. Surprisingly, parasite performance was weakest when attacking a leguminous host, although parasite total nitrogen was highest when growing on a legume. Parasites also exerted a strong direct effect on host performance: host dry mass was negatively correlated with parasite mass for all three host species tested. However, this effect differed among hosts: for E. staechadifolium, proportionately larger parasite mass was correlated with smaller overall biomass of the host and parasite combined, while for the other two hosts, overall host—parasite mass was not correlated with parasite mass, indicating that E. staechadifolium was more affected by parasite attack than were the other host species. Finally, host plant chemistry had strong indirect effects on the performance of an aphid, Nearctaphis kachena, that feeds on C. wightii. Aphids feeding on C. wightii that were parasitizing L. arboreus (alkaloid—producing, high nitrogen), A. pycnocephala (alkaloid—free, intermediate nitrogen), and E. staechadifolium (terpenoid—producing, low nitrogen) experienced 68.2, 65.3, and 49.5% survival, respectively. Further, aphids feeding on parasites using L. arboreus and A. pycnocephala produced 2.43 and 1.77 times more offspring on average than those feeding on parasites using E. staechadifolium. My results indicate that interactions between plant parasites and different host species can have strong direct effects on both host and parasite performance, as well as marked effects on the tritrophic interactions among plant hosts, parasitic plants, and their herbivores.

ISSN:0012-9658    

DOI:10.2307/2265537

出版商:Ecological Society of America    

年代:1996

数据来源: WILEY