John N. Thompson

Evolutionary ecology of the relationship between oviposition preference and performance of offspring in phytophagous insects

The relationship between oviposition preference and growth, survival, and reproduction of offspring is the crux of the problem in the evolution of host associations between phytophagous insects and plants. Observed relationships between oviposition preference and performance of offspring range from good to poor. At least four hypotheses have been suggested to explain observed use of particular host plants that may not result in the fastest growth rates or greatest pupal masses: time, patch dynamics, parasite versus grazer lifestyles, and enemy‐free space. Our current understanding of these relationships, however, is hampered by an almost complete lack of data on how preference and performance are related genetically. These data are needed to understand the origins of covariance between preference and performance and constraints on the evolution of host associations.

Rapid evolution as an ecological process

Rapid evolution of interspecific interactions (during a timespan of about 100 years) has the potential to be an important influence on the ecological dynamics of communities. However, despite the growing number of examples, rapid evolution is still not a standard working hypothesis for many ecological studies on the dynamics of population structure or the organization of communities. Analysis of rapid evolution as an ecological process has the potential to make evolutionary ecology one of the most central of applied biological sciences.

Specific Hypotheses on the Geographic Mosaic of Coevolution

Coevolution is one of the major processes organizing the earths biodiversity. The need to understand coevolution as an ongoing process has grown as ecological concerns have risen over the dynamics of rapidly changing biological communities, the conservation of genetic diversity, and the population biology of diseases. The biggest current challenge is to understand how coevolution operates across broad geographic landscapes, linking local ecological processes with phylogeographic patterns. The geographic mosaic theory of coevolution provides a framework for asking how coevolution continually reshapes interactions across different spatial and temporal scales. It produces specific hypotheses on how geographically structured coevolution differs from coevolution at the local scale. It also provides a framework for understanding how local maladaptation can result from coevolution and why coevolved interactions may rarely produce long lists of coevolved traits that become fixed within species. Long‐term field studies of the same interaction across multiple communities and spatially structured mathematical models are together beginning to show that coevolution may be a more important ongoing process than had been indicated by earlier empirical and theoretical studies lacking a geographic perspective.

Patch dynamics and the design of nature reserves

Abstract Island biogeographic theory has been applied to the design of nature reserves. However, immigration, which is important in maintaining species equilibrium on true islands, will not contribute significantly to the maintenance of equilibrium on reserves in the future because of the disappearance of recolonisation sources. Consequently, extinction becomes the dominant population process, and the internal disturbance dynamics become the critical design feature of reserves. The design of reserves should be based on ‘minimum dynamic area’, the smallest area with a natural disturbance regime which maintains internal recolonisation sources and hence minimises extinctions. Determination of minimum dynamic area must be based on knowledge of disturbance-generated patch size, frequency, and longevity, and the mobilities of the preserved species. These features have not all been explicitly considered in the previous island biogeographic design recommendations.

Statistical Analysis of Survival and Removal Rate Experiments

We consider both parametric and nonparametric statistical analyses of survivorship curves and of removal rates, including assumptions, tests, ecological applications, and the difference between censored and uncensored survival data. For censored data, the Gehan—Wilcoxon test, the longrank test, and the likelihood ratio test and appropriate and are readily available in mainframe computer statistical packages. In cohort analyses, these tests can determine if cohorts of different ages have different age—specific death rates or different death rates over the same time period. See full-text article at JSTOR

EVOLUTION IN STEPPE WITH FEW LARGE, HOOVED MAMMALS

The morphology of rhizomatous and caespitose grasses reflects the two extremes to which perennial grasses have evolved at least in partial response to continuous high versus low selection pressure by large congregating mammals. In North America steppe of the Bouteloua Province east of the Rockies is dominated by a mix of mainly rhizomatous C3 and C4 grasses which have long been associated with large herds of Bison and more recently with cattle. Introduction of cattle into these grasslands had much less effect on community structure than did livestock introduction into steppe of the Agropyron Province west of the Rockies which lacked large herds of mammals throughout the Holocene (and perhaps earlier). The underlying cause of native ungulate sparseness may have been related to the moisture cycle of the Prevailing Westerlies, which may have largely excluded C4 species, thereby severely controlling Bison numbers. In these communities both the dominant C3 caespitose grasses and the prominent cryptogam layer were soon destroyed by domestic ungulates and replaced largely by alien winter annuals. The relative changes in these two Provinces over the past 200 yr illustrate the importance in plants of herbivore-adapted traits in generating the overall physiognomy of some steppes and the resiliency of those grasslands to the introduction of novel selection pressure.

Geographic structure and dynamics of coevolutionary selection

Coevolution of species is one of the major processes organizing the Earths biodiversity. Recent coevolutionary theory has indicated that the geographic structure of species has the potential to impose powerful and continuing effects on coevolutionary dynamics, if that structure creates selection mosaics and coevolutionary hotspots across landscapes. Here we confirm that current coevolutionary selection in interspecific interactions can be highly divergent across both narrow and broad geographic scales, thereby fuelling continuing coevolution of taxa. Study of a widespread plant–insect interaction across a broad range of habitats for several years showed that an insect functioning both as a pollinator and a floral parasite can be strongly mutualistic in some habitats but commensal or antagonistic in neighbouring habitats. The results for one of the habitats span seven years, demonstrating that the local structure of coevolutionary selection can remain stable across multiple generations. Conservation of the evolutionary processes maintaining long-term biological diversity may require preservation of the conditions that allow a long-term shifting geographic mosaic of coevolutionary hotspots and coldspots.

The dynamics of evolutionary stasis

Abstract The fossil record displays remarkable stasis in many species over long time periods, yet studies of extant populations often reveal rapid phenotypic evolution and genetic differentiation among populations. Recent advances in our understanding of the fossil record and in population genetics and evolutionary ecology point to the complex geographic structure of species being fundamental to resolution of how taxa can commonly exhibit both short-term evolutionary dynamics and long-term stasis.

Nutritional Values of Wild Fruits and Consumption by Migrant Frugivorous Birds

To learn some of the bases for consumption of temperate fleshy fruits by birds, we examined nutritional and morphological traits of temperate fleshy fruits and made laboratory obser? vations on consumption of individual fruit species using 18 fruit species and 11 migrant frugivorous bird species in Illinois. The only seasonal trends in fruit traits were interspecific increases in absolute quantity of potassium and protein per fruit. Fruit energy content did not differ among species having bicolored vs. monochrome or small vs. large fruit displays. The fruit mass consumed was correlated best with dry pulp mass per fruit, providing significant positive correlations in 6 of 11 frugivorous species. Large fruit size relative to bill size did not appear to affect fruit consumption over the range of fruit sizes and bird species used. Because retained energy was correlated with mass consumed, the fruit pulp mass consumed was in most cases a good index of the energy obtained. Some significant differences occurred in digestive efficiency of a bird species eating different fruit species, and among different bird species eating a single fruit species, but no trends were apparent. Regurgitated seeds generally spent less time in a bird than did defecated seeds, facilitating more rapid disposal of seed ballast. Smaller birds defecated only small seeds and regurgitated some small seeds as well as all large ones, whereas larger birds defecated all smaller seeds and many larger ones. Consequently, resultant seed shadows may depend upon both bird and seed size.

EVOLUTION OF TEMPERATE FRUIT/BIRD INTERACTIONS: PHENOLOGICAL STRATEGIES

Evolving relationships between animals and plants are often patchy in their occurrence in both space and time. If the relationship is mutualistic, selection should act to maximize the probability of interaction between the participants. In the mutualistic interactions between temperate fleshy fruits and birds, the timing of fruit ripening affects the probability of seed dispersal by birds. Rapid removal of ripe fruits is important for some summer and fall fruiting species because of a high probability of fruit destruction by invertebrates (Thompson and Willson, 1978). Production of fruits at a time when birds do not remove them may be selectively disadvantageous in that destruction by invertebrates precludes successful dispersal. Therefore, bird-dispersed plants in temperate regions are commonly supposed to ripen their fruits in fall, after the avian breeding season during which birds often concentrate on insects (Morton, 1973) and during the fall migration (Snow, 1971; Stebbins, 1971). This paper examines the selective pressures acting on the seasonal timing of mutualistic interactions between temperate fleshy fruits and birds. Specifically, it (1) compares the removal rates of mid-latitude fruits before, during and after fall bird migrations, (2) analyzes seasonal variation in the ripening patterns of plants in the context of frugivore availability, and (3) provides a theoretical framework for future work on the phenology of temperate fruit/bird interactions. A fleshy