John M. Eadie

Density Dependence, Frequency Dependence, and Alternative Nesting Strategies in Goldeneyes

We develop a simple model to explore the conditions under which intraspecific brood parasitism would be evolutionarily stable in a cavity-nesting bird, the Barrows goldeneye. Our results show that parasitism can be maintained by negative frequency-dependent selection, which is consistent with recent speculations. However, when we include the effects of density dependence, we find a density threshold below which frequency-dependent effects on fitness are negligible but above which frequency dependence plays a prominent role. Patterns consistent with either a mixed evolutionarily stable strategy (ESS) or a conditional ESS can therefore be obtained simply by varying population density. These results may provide an explanation for contradictory patterns found in a previous field study of brood parasitism in goldeneyes. More generally, our results indicate that conclusions about the adaptive basis of alternative reproductive behaviors can be influenced strongly by population demography. Evolutionarily stable strategy theory holds that mixed and conditional ESSs are mutually exclusive, yet we suggest that attempts to test between these alternatives in field studies may meet with limited success if population density varies.

Cooperation, Conflict, and Crèching Behavior in Goldeneye Ducks

Crèching behavior, or brood amalgamation, results in offspring being reared by adults other than their genetic parents. Although a variety of hypotheses have been proposed to explain this behavior, most assume either that brood amalgamation is accidental (i.e., nonselected) or that adoption of young is selected for because of social benefits to the young and/or adopting parents. We propose, instead, that brood amalgamation is a function of two separate processes: brood desertion and brood adoption. To examine brood desertion, we develop a graphic model to predict when parents should abandon their young and we test this model experimentally for the Barrows goldeneye (Bucephala islandica). As predicted, females deserted their offspring when the size of the brood was experimentally reduced. Brood adoption occurred when deserted ducklings joined other broods. However, the success of ducklings in doing so was strongly dependent on the availability of potential host broods and on the age of the recipient broods. Foreign ducklings were readily accepted into young broods (<10 d old) but invariably were rejected from old broods. We could detect no benefits or costs of brood adoption to the host females, contrary to the expectations of a social benefit hypothesis. Our experiments indicate that Crèching behavior is driven by selection on adults to abandon their brood when the benefits of continued investment are outweighed by the reduction in future reproduction and selection on deserted ducklings to join other broods to obtain parental care. Rather than a form of cooperative brood care, Crèching in goldeneyes is perhaps best considered as a form of reproductive parasitism, entailing parent‐offspring conflict over brood desertion and intergenerational conflict over adoption of abandoned young.

The allometric relationship between resting metabolic rate and body mass in wild waterfowl (Anatidae) and an application to estimation of winter habitat requirements

Abstract We examined the allometric relationship between resting metabolic rate (RMR; kJ day−1) and body mass (kg) in wild waterfowl (Anatidae) by regressing RMR on body mass using species means from data obtained from published literature (18 sources, 54 measurements, 24 species; all data from captive birds). There was no significant difference among measurements from the rest (night; n = 37), active (day; n = 14), and unspecified (n = 3) phases of the daily cycle (P > 0.10), and we pooled these measurements for analysis. The resulting power function (aMassb) for all waterfowl (swans, geese, and ducks) had an exponent (b; slope of the regression) of 0.74, indistinguishable from that determined with commonly used general equations for nonpasserine birds (0.72–0.73). In contrast, the mass proportionality coefficient (b; y-intercept at mass = 1 kg) of 422 exceeded that obtained from the nonpasserine equations by 29%–37%. Analyses using independent contrasts correcting for phylogeny did not substantially alter the equation. Our results suggest the waterfowl equation provides a more appropriate estimate of RMR for bioenergetics analyses of waterfowl than do the general nonpasserine equations. When adjusted with a multiple to account for energy costs of free living, the waterfowl equation better estimates daily energy expenditure. Using this equation, we estimated that the extent of wetland habitat required to support wintering waterfowl populations could be 37%–50% higher than previously predicted using general nonpasserine equations.

Size Ratios and Artifacts: Hutchinson's Rule Revisited

We show that size ratios within the range predicted by Hutchinsons rule invariably result, given only that animal sizes are distributed lognormally and that the variances of these distributions are small. We argue that both these conditions are properties of a wide variety of animate and inanimate objects in nature, and therefore size ratios tell us little about the processes structuring animal communities. Our results confirm previous suggestions that Hutchinsons constant is an artifact, and we present a reasonable mechanism to suggest how such an artifact might arise.

USING SPECIES-HABITAT MODELS TO TARGET CONSERVATION: A CASE STUDY WITH BREEDING MALLARDS

To make effective conservation decisions, managers must understand the ecology of species targeted for conservation and be able to apply that knowledge in decision-making. Most conservation research to date has focused on the first of these requirements, but lately ecologists and others have begun to address more systematically the decision-making component of conservation. In this paper, we develop an explicit model of species– habitat relations and incorporate it into an optimization framework for prioritizing sites for management. We then present a case study that applies these concepts to choosing sites for wetlands restoration to benefit breeding Mallards (Anas platyrhynchos) in the Central Valley of California, USA. First, a model of habitat selection by Mallards was estimated using count regression techniques. Our results indicate that breeding Mallard abundances depend not only on the amount of each land use type present, but also on the interspersion of particular land use types in the vicinity o...

Power of the Concentrated Changes Test for Correlated Evolution

The concentrated changes test (CCT) calculates the probability that changes in a binary character are distributed randomly on the branches of a cladogram. This test is used to examine hypotheses of correlated evolution, especially cases where changes in the state of one character influence changes in the state of another character. The test may be sensitive to the addition of branches that lack either trait of interest (white branches). To examine the effects of the proportion of white branches and of tree topology on the CCT probability, we conducted a simulation analysis using a series of randomly generated 100-taxon trees, in addition to a nearly perfectly balanced (symmetrical) and a completely imbalanced (asymmetrical) 100-taxon tree. Using two models of evolution (gains only, or gains and losses), we evolved character pairs randomly onto these trees to simulate cases where (1) characters evolve independently (i.e., no correlation among the traits) or (2) all changes in the dependent character occur on branches containing the independent trait (i.e., a strong correlation among the traits). This allowed us to evaluate the sensitivity of the CCT to type I and type II errors, respectively. In the simulations, the CCT did not appear to be overly sensitive to the inclusion of white branches (low likelihood of type I error with both CCT probabilities < 0.05 and < 0.01). However, the CCT was susceptible to type II error when the proportion of white branches was < 20%. The test was also sensitive to tree shape and was positively correlated to Collesss tree imbalance statistic I. Finally, the CCT responded differently for simulations where only gains were allowed and those where both gains and losses were permitted. These results indicate that the CCT is unlikely to detect a correlation between characters when no such correlation exists. However, when a trait can be gained but not lost, the CCT is conservative and may fail to detect true correlations among traits (increased type II error). Determination of the sampling universe (the taxa included in the comparative analysis) can strongly influence the probability of making such type II errors. We suggest guidelines to circumvent these limitations.

An obligate brood parasite trapped in the intraspecific arms race of its hosts

Reciprocal selection pressures often lead to close and adaptive matching of traits in coevolved species. A failure of one species to match the evolutionary trajectories of another is often attributed to evolutionary lags or to differing selection pressures across a geographic mosaic. Here we show that mismatches in adaptation of interacting species—an obligate brood parasitic duck and each of its two main hosts—are best explained by the evolutionary dynamics within the host species. Rejection of the brood parasites eggs was common by both hosts, despite a lack of detectable cost of parasitism to the hosts. Egg rejection markedly reduced parasite fitness, but egg mimicry experiments revealed no phenotypic natural selection for more mimetic parasitic eggs. These paradoxical results were resolved by the discovery of intraspecific brood parasitism and conspecific egg rejection within the hosts themselves. The apparent arms race between species seems instead to be an incidental by-product of within-species conflict, with little recourse for evolutionary response by the parasite.

Another genetically promiscuous ‘polygynous’ mammal: Mating system variation in Neotoma fuscipes

Polygyny is widely thought to be the dominant mating system in mammals. However, more recent genetic work casts doubt on this view. Variation in mating systems has been found in both males and females within and across mammalian species. The causes and consequences of mating system variation have important implications for understanding the population and evolutionary dynamics of species. To better understand mating system variation, both in mammals and more generally, this study analyses genetic mating system variation in dusky-footed woodrats, Neotoma fuscipes. Contrary to expectation, there was little support for polygyny at the genetic level. Instead, the study populations were characterized by promiscuity and monogamy, in both males and females. At higher densities, variance in the numbers of mates and offspring were higher in breeding males than in females, as is often observed. However, this trend was reversed in low-density, coniferous forest habitat. Model selection revealed that the best model of successfully mated pairs includes population density, operational sex ratio and individual pairwise distances as predictors. Higher densities coupled with male-biased sex ratios appear to decrease the probability of mating and decrease opportunities for polygamy, particularly in females. Although woodrats display sexual size dimorphism, male body size had no detectable effect on mating success. This study questions the prevalence of polygyny in mammals and demonstrates the need for more detailed, genetic investigations of mating systems. Future studies are needed to explore the complex interactions among mating system determinants and test hypotheses of sex-specific mating system variation.

Local genetic structure and relatedness in a solitary mammal, Neotoma fuscipes

Due to a publisher’s error, this article incorrectly credits the Ecology Graduate Group with authorship. The correct citation of this article is the following: McEachern MB, Eadie JM, Van Vuren DH (2007) Local genetic structure and relatedness in a solitarymammal,Neotoma fuscipes. Behav Ecol Sociobiol. DOI 10.1007/s00265-0070378-2. Behav Ecol Sociobiol (2007) 61:1507 DOI 10.1007/s00265-007-0401-7

Reverse sex‐biased philopatry in a cooperative bird: genetic consequences and a social cause

The genetic structure of a group or population of organisms can profoundly influence the potential for inbreeding and, through this, can affect both dispersal strategies and mating systems. We used estimates of genetic relatedness as well as likelihood‐based methods to reconstruct social group composition and examine sex biases in dispersal in a Costa Rican population of white‐throated magpie‐jays (Calocitta formosa, Swainson 1827), one of the few birds suggested to have female‐biased natal philopatry. We found that females within groups were more closely related than males, which is consistent with observational data indicating that males disperse upon maturity, whereas females tend to remain in their natal territories and act as helpers. In addition, males were generally unrelated to one another within groups, suggesting that males do not disperse with or towards relatives. Finally, within social groups, female helpers were less related to male than female breeders, suggesting greater male turnover within groups. This last result indicates that within the natal group, female offspring have more opportunities than males to mate with nonrelatives, which might help to explain the unusual pattern of female‐biased philopatry and male‐biased dispersal in this system. We suggest that the novel approach adopted here is likely to be particularly useful for short‐term studies or those conducted on rare or difficult‐to‐observe species, as it allows one to establish general patterns of philopatry and genetic structure without the need for long‐term monitoring of identifiable individuals.