Lizards speed up visual displays in noisy motion habitats

Extensive research over the last few decades has revealed that many acoustically communicating animals compensate for the masking effect of background noise by changing the structure of their signals. Familiar examples include birds using acoustic properties that enhance the transmission of vocalizations in noisy habitats. Here, we show that the effects of background noise on communication signals are not limited to the acoustic modality, and that visual noise from windblown vegetation has an equally important influence on the production of dynamic visual displays. We found that two species of Puerto Rican lizard, Anolis cristatellus and A. gundlachi, increase the speed of body movements used in territorial signalling to apparently improve communication in visually 'noisy' environments of rapidly moving vegetation. This is the first evidence that animals change how they produce dynamic visual signals when communicating in noisy motion habitats. Taken together with previous work on acoustic communication, our results show that animals with very different sensory ecologies can face similar environmental constraints and adopt remarkably similar strategies to overcome these constraints.

Growth-mortality tradeoffs and 'personality traits' in animals

Consistent individual differences in boldness, reactivity, aggressiveness, and other 'personality traits' in animals are stable within individuals but vary across individuals, for reasons which are currently obscure. Here, I suggest that consistent individual differences in growth rates encourage consistent individual differences in behavior patterns that contribute to growth-mortality tradeoffs. This hypothesis predicts that behavior patterns that increase both growth and mortality rates (e.g. foraging under predation risk, aggressive defense of feeding territories) will be positively correlated with one another across individuals, that selection for high growth rates will increase mean levels of potentially risky behavior across populations, and that within populations, faster-growing individuals will take more risks in foraging contexts than slower-growing individuals. Tentative empirical support for these predictions suggests that a growth-mortality perspective may help explain some of the consistent individual differences in behavioral traits that have been reported in fish, amphibians, reptiles, and other animals with indeterminate growth.

The silver spoon effect and habitat selection by natal dispersers

The silver spoon effect in the context of habitat selection occurs when dispersers in good condition are more likely to settle in high-quality habitats than dispersers in poor condition. Positive relationships between disperser condition and the quality of post-dispersal habitats are predicted by at least two non-exclusive ultimate hypotheses. The competition hypothesis assumes that a disperser's condition affects its chances of competing for space or joining an established group after arriving at a high-quality habitat, while the search hypothesis assumes that a disperser's condition affects its selectivity, and hence its chances of accepting a lower-quality habitat when it is searching for a new habitat. Thus far, silver spoon effects in the context of habitat selection have been reported in only a handful of species (several birds and marine invertebrates), but this study suggests that they may be relatively common in particular species and situations.

Territory acquisition in lizards. IV. Obtaining high status and exclusive home ranges

We released juvenile Anolis aeneus lizards into vacant patches of habitat in the field and observed as they established territories. Individuals settling in the presence of few competitors obtained more exclusive home ranges than did individuals settling at higher densities. When settling at high densities, juveniles that eventually attained high social status fought and chased their opponents more frequently than did juveniles that were subordinate to other residents at the end of the settlement period. With respect to predicting an individual's final status and space use, however, the fact that it fought other settlers was more important than the outcome of those fights. Results from this and previous studies in this series are consistent with a general model of territory establishment that includes assumptions about the value of familiar space, the costs of aggressive interactions and the ability of settlers to form predictable social relationships with one another.Copyright 1998 The Association for the Study of Animal Behaviour.

Estimating asymptotic size using the largest individuals per sample

Estimates of asymptotic size are especially useful for comparative studies of taxonomic groups in which animals mature at small sizes relative to their final asymptotic sizes. The largest individuals per sample can provide reasonable estimates of asymptotic size if three conditions are met: 1) at least some adults in a population are near their final asymptotic size, 2) samples of a reasonable size are likely to contain a 'largest individual' that is near the average asymptotic size for the members of its sex, and 3) the coefficient of variation in asymptotic size is small for the members of each sex. In the current study, we show that all three of these conditions are met for one species of Anolis lizards (A. limifrons). For a series of samples from the genus Anolis, the largest individual per sample produces estimates of asymptotic size that are virtually identical to those produced by fitting field data on growth rates to nonlinear growth equations. These results suggest that the largest individual method can provide reasonable estimates of asymptotic size for the members of this genus, and imply that this method may also be useful for estimating asymptotic sizes in other taxa that satisfy the criteria listed above.