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T W Schoener

Publications and source records attributed to T W Schoener.

11 recordsLinked to original sources
PubMed2001

Natural restoration of the species-area relation for a lizard after a hurricane.

We document the decimation and recovery of the commonest lizard species, Anolis sagrei, on 66 islands in the Bahamas that were directly hit by Hurricane Floyd in September 1999. Before the hurricane, an island's area was a better predictor of the occurrence of A. sagrei than was its altitude. Immediately after, altitude was a better predictor: Apparently all lizards on islands lower than about 3 meters maximum elevation perished in the storm surge. After about 1 year, area again became the better predictor. By 19 months after the hurricane, A. sagrei populations occurred on 88% of the islands they formerly occupied. Recovery occurred via overwater colonization and propagation from eggs that survived inundation, mechanisms that were enhanced by larger island area. Thus, natural processes first destroyed and then quickly restored a highly regular species-area distribution.

Altitude↗
PubMed2001

Predators increase the risk of catastrophic extinction of prey populations.

There has been considerable research on both top-down effects and on disturbances in ecological communities; however, the interaction between the two, when the disturbance is catastrophic, has rarely been examined. Predators may increase the probability of prey extinction resulting from a catastrophic disturbance both by reducing prey population size and by changing ecological traits of prey individuals such as habitat characteristics in a way that increases the vulnerability of prey species to extinction. We show that a major hurricane in the Bahamas led to the extinction of lizard populations on most islands onto which a predator had been experimentally introduced, whereas no populations became extinct on control islands. Before the hurricane, the predator had reduced prey populations to about half of those on control islands. Two months after the hurricane, we found only recently hatched individuals--apparently lizards survived the inundating storm surge only as eggs. On predator-introduction islands, those hatchling populations were a smaller fraction of pre-hurricane populations than on control islands. Egg survival allowed rapid recovery of prey populations to pre-hurricane levels on all control islands but on only a third of predator-introduction islands--the other two-thirds lost their prey populations. Thus climatic disturbance compounded by predation brought prey populations to extinction.

Animals↗
PubMed2001

Experimental studies of adaptive differentiation in Bahamian Anolis lizards.

Populations of the lizards Anolis carolinensis and A. sagrei were experimentally introduced onto small islands in the Bahamas. Less than 15 years after introduction, we investigated whether the populations had diverged and, if so, whether differentiation was related to island vegetational characteristics or propagule size. No effect of founding population size was evident, but differentiation of A. sagrei appears to have been adaptive, a direct relationship existed between how vegetationally different an experimental island was from the source island and how much the experimental population on that island had diverged morphologically. Populations of A. carolinensis had also diverged, but were too few for quantitative comparisons. A parallel exists between the divergence of experimental populations of A. sagrei and the adaptive radiation of Anolis lizards in the Greater Antilles; in both cases, relative hindlimb length and perch diameter are strongly correlated. This differentiation could have resulted from genetic change or environmentally-driven phenotypic plasticity. Laboratory studies on A. sagrei from a population in Florida indicate that hindlimb length exhibits adaptive phenotypic plasticity. Further studies are required to determine if the observed differences among the experimental populations are the result of such plasticity. Regardless of whether the differences result from plasticity, genetic change, or both, the observation that anole populations differentiate rapidly and adaptively when exposed to novel environmental conditions has important implications for understanding the adaptive radiation of Caribbean anoles.

Adaptation, Biological↗
PubMed2000

The relationship between sexual size dimorphism and habitat use in Greater Antillean Anolis lizards.

Sexual size dimorphism (SSD) is the evolutionary result of selection operating differently on the body sizes of males and females. Anolis lizard species of the Greater Antilles have been classified into ecomorph classes, largely on the basis of their structural habitat (perch height and diameter). We show that the major ecomorph classes differ in degree of SSD. At least two SSD classes are supported: high SSD (trunk-crown, trunk-ground) and low SSD (trunk, crown-giant, grass-bush, twig). Differences cannot be attributed to an allometric increase of SSD with body size or to a phylogenetic effect. A third explanation, that selective pressures on male and/or female body size vary among habitat types, is examined by evaluating expectations from the major relevant kinds of selective pressures. Although no one kind of selective pressure produces expectations consistent with all of the information, competition with respect to structural habitat and sexual selection pressures are more likely possibilities than competition with respect to prey size or optimal feeding pressures. The existence of habitat-specific sexual dimorphism suggests that adaptation of Anolis species to their environment is more complex than previously appreciated.

Animals↗
PubMed1987

Leaf pubescence in buttonwood: Community variation in a putative defense against defoliation.

Plants have a variety of putative defenses against defoliation by herbivores, among which are pubescent leaves. Buttonwood (Conocarpus erectus), a Caribbean tree, shows considerable between-individual variation in this trait, and pubescent leaves have less herbivore damage. Surveying 97 island communities, I documented three patterns expected were pubescent individuals more frequent where herbivory is great. (i) Larger islands have a higher percentage of pubescence (larger islands have more herbivores). (ii) Islands nearer to a mainland have a higher percentage of pubescence (nearer islands receive more herbivore immigrants). (iii) Islands having an extremely abundant predator on foliage arthropods, arboreal lizards, have a smaller percentage of pubescence than no-lizard islands. The third effect, though statistically significant, is weak relative to the direct effects of lizards on one category of their prey (spiders) measured in the same system.

Journal Article↗
PubMed1974

The compression hypothesis and temporal resource partitioning.

Contingency models of feeding compare the energy per unit time gained from utilizing a resource unit of a particular kind (food types, habitat patches, time periods) against that energy/time expected if the unit is skipped. Optimally, an animal should reject the particular unit if and only if the former energy/time is less than the latter. Consequently, food or habitat types should be excluded if the prospect of finding and consuming better types is sufficiently high. In contrast, feeding periods should be skipped only if it is less costly to wait than to feed.In situations of high food abundance, contingency models imply that animals should be maximally specialized with respect to food or habitat type, but maximally generalized with respect to time period. As food decreases in abundance, food and habitat types should be added to the diet or itinerary, but time periods should be omitted from feeding activity. In contrast, animals with fixed caloric intake should broaden diet, habitat, and feeding times as abundance decreases.According to contingency models, competitors cannot cause item kinds to be dropped from the diet, but because they can affect the values of patches once found, can cause habitat kinds to be dropped from the itinerary. Competitors also reduct the value of feeding during particular time periods, but ordinarily fairly severe depletion must occur before it is optimal to feed no longer in a period frequented by competitors.These arguments imply that temporal resource partitioning on a diel basis should be relatively rare. In fact, specialization according to feeding period should differentially occur in animals of limited abilities to use or process available food, whereas that need not be the case for food-type or habitat specialization. It should also occur in animals sensitive to and found in variable climates.

Journal Article↗