Astrid Kodric-Brown

Turnover Rates in Insular Biogeography: Effect of Immigration on Extinction

Demographic and genetic contributions from nonspecific immigrants tend to reduce ex- tinction rates of insular populations. The MacArthur-Wilson model of island biogeography is modified to provide for this effect of immigration on extinction, which we call the rescue effect. This new model predicts that when immigration rates are high relative to extinction rates, turnover rate is directly related to the distance between an island and the source of colonizing species. A field study of the distribution of arthropods among isolated plants supports the model.

TRUTH IN ADVERTISING: THE KINDS OF TRAITS FAVORED BY SEXUAL SELECTION

The truth in advertising model describes a mechanism of sexual selection to account for the evolution of the kinds of traits used by males of polygynous species to compete for and attract mates. Sexual selection favors the display of male traits that vary phenotypically within and among individuals in such a way as to maintain a positive correlation between the degree of expression of the traits and overall genetic fitness. Because the exaggerated expression of these traits requires allocation of limited resources to reproduction, it reflects age, nutritional condition, social status, and resistance to predators and pathogens. It is advantageous to females to choose as mates individuals with such exaggerated traits (and also those that have won aggressive bouts with other males) because these traits honestly advertise desirable attributes that can be passed on to both male and female offspring. By stressing the relationship between sexual traits and overall male fitness, this model deemphasizes the traditional dichotomies between the effects of sexual selection and natural selection and between female choice and male-male competition as mechanisms of sexual selection. Necessary conditions and predicted consequences of the truth in advertising mechanism are illustrated with examples of antlers of deer and nuptial coloration in fishes.

Dietary carotenoids and male mating success in the guppy: an environmental component to female choice

SummaryThis study examined the relationship between dietary carotenoids, female choice, and male mating success in the guppy, Poecilia reticulata. Using a split-brood design, male siblings were either raised on a diet enhanced with astaxanthin and canthaxin or fed a basal diet without carotenoids. Males were photographed, and the location, size, and brightness of their red and orange pigment spots on the body were measured. Courtship behaviors were recorded during visual and mating trials. Males fed the carotenoid-enhanced diet had red and orange spots that averaged 2.5 times brighter, spent significantly more time near the female in visual response trials, were preferred by females in visual choice tests, and had a higher mating success than their siblings raised on the carotenoid-free diet. Diet did not affect male size, location or size of the red and orange pigment spots, or the intensity of courtship behavior. The results of this study show that females respond to environmentally-induced variation in the expression of a secondary sexual trait and that this has important consequences for male mating success.

Influence of Economics, Interspecific Competition, and Sexual Dimorphism on Territoriality of Migrant Rufous Hummingbirds

Migrant Rufous Hummingbirds (Selasphorus rufus) arrive in eastern Arizona in late summer and establish feeding territories from which other hummingbirds are excluded. Territories vary 100-fold in area and 5-fold in number of flowers. A simple cost-benefit model accounts for observed variation in territory size and number of flowers defended. Both sexes defend territories, but d d utilize denser flowers than Y Y. These differences appear to be related to sexual dimorphism in wing disc loading. Selasphorus rufus appears to have sacrificed efficient flight for aggressive ability as a strategy for competing with resident hummingbird species during its migration. Comparison of feeding territories of S. rufus and other nectarivorous birds indicate similarities which suggest that these systems may be subject to similar economic constraints.

CONVERGENCE, COMPETITION, AND MIMICRY IN A TEMPERATE COMMUNITY OF HUMMINGBIRD-POLLINATED FLOWERS'

We studied the pollination ecology of nine species of red, tubular flowers which bloom together in different combinations in the White Mountains of Arizona, USA. All species were strik- ingly convergent in floral color, size, and shape. Hummingbirds, the primary pollinators, usually did not visit flower species selectively, and individual birds often simultaneously carried four or more species of pollen. Flowers may have competed interspecifically for these shared pollinators, but competition was reduced because character displacement in orientation of anthers and stigma resulted in some species using different parts of the bird to transport their pollen. Most flower species secreted nectar at similar rates, particularly when they bloomed together in mixed stands. A population of Lobelia cardinalis secreted no nectar; it attracted hummingbirds by mimicing more abundant, nectar- producing species. This temperate flower community, which resembles some associations of conver- gent Mullerian and Batesian mimics, appears to have evolved its characteristic convergent structure because the advantages of using similar signals and rewards to share the same hummingbird pollinators outweigh the advantages of diverging to reduce interspecific competition.

Female choice of multiple male criteria in guppies: interacting effects of dominance, coloration and courtship

SummaryI experimentally examined the relative importance of social dominance, color patterns, and courtship behavior in male mating and reproductive success in the guppy Poecilia reticulata. Female choice of males is based on a complex set of behavioral and morphological traits. The results of 59 paired-male one-female visual choice and mating trials showed that male mating success was positively correlated with dominance, courtship intensity, and male coloration. Only dominant males engaged in full copoulations, and they sired two-thirds of the broods. An analysis of the paternity of broods and results of mating trials showed that a females visual response when the sexes are separated by a glass partition is a good predictor of a males reproductive success when the partition is removed and they are allowed to mate. A canonical correlation analysis of male behavioral and morphological traits indicated that female visual response and male mating success were positively correlated with male courtship and with agonistic behavior. However, the relative importance of color varied. Carotenoid and iridescent spots were important both in attracting the females attention and in enhancing male mating success. Melanins were not correlated with either mating success or female response. There was a relatively low correlation (48%) between male behavioral and morphological variables and female response variables (full copulation and female visual response). These results suggest that female choice is subtle, and is based on a complex suite of male behavioral and morphological traits as well as on competitive interactions among males.

Metabolic Ecology:A Scaling Approach

Most of ecology is about metabolism: the ways that organisms use energy and materials. The energy requirements of individuals - their metabolic rates - vary predictably with their body size and temperature. Ecological interactions are exchanges of energy and materials between organisms and their environments. So metabolic rate affects ecological processes at all levels: individuals, populations, communities and ecosystems. Each chapter focuses on a different process, level of organization, or kind of organism. It lays a conceptual foundation and presents empirical examples. Together, the chapters provide an integrated framework that holds the promise for a unified theory of ecology.

Female choice in the guppy (Poecilia reticulata): the interaction between male color and display

Abstract. The effect of two components of male courtship, color and display behavior, on female choice of mates was investigated in the guppy (Poecilia reticulata). Computer-modified videos were constructed to determine the relative importance of a static trait, the presence or absence of carotenoid pigment (C and NC), and a dynamic trait, high and low display rate (HD and LD), on female response. Females were given a choice between all combinations of male display and color in a binary choice design. Preference was determined by the time females spent visually inspecting the animation. Females preferred animations with high display rates when both animations displayed color (CHD vs CLD), but not in the absence of color (NCHD vs NCLD). Equal numbers of females chose the color/low-display animation and the no-color/high-display animation when the two were paired. Conversely, color became a criterion of choice when both animations showed a low display rate (CLD vs NCLD), but not when both displayed at a high rate (CHD vs NCHD). These results suggest that females use both static and dynamic traits to evaluate males, but their rankings are affected by the choices available. Results of these experiments provide insights into how females use multiple traits to assess males.

Highly structured fish communities in Australian desert springs

To assess the pattern and causes of community structure, we sampled 38 isolated springs in the Dalhousie Basin of South Australia to determine the distributions of five taxa of native fishes. We visited each spring on at least two consecutive days, used several collecting methods to determine the presence of absence of each taxon, and took standardized measurements of abiotic environmental variables. Community organization was highly predictable: (1) number of species increased with spring size, (2) each species occurred in nearly all springs larger than a certain size, and (3) species composition exhibited nearly perfect nestedness. These results suggest that much of the variation in the composition of other communities may not be stochastic. When the influence of historical and environmental factors can be assessed, the colonization—extinction processes and ecological relationships that determine community structure may be highly deterministic.

Repeatability of female choice in the guppy: response to live and videotaped males

The degree to which females are consistent in their mate preferences has implications for studies of sexual selection. Because choice of females for particular males may be affected by temporal changes in male characteristics, consistency of mate preferences of individual females of Poecilia reticulata was studied by presenting them with the same male pairs in consecutive trials under three experimental procedures: live males behind clear glass, live males behind one-way glass and images of males on videotape. Although females did not habituate to males in any of the experiments, they spent significantly more time in proximity to males behind clear glass than in the video and one-way glass presentations. Females preferred the bright male over the pale one in the video and the clear glass presentations, but not in the one-way glass experiment. Repeatability of preferences by individual females for a male was high in the video and one-way glass presentations but low in the clear-glass experiment. Behavioural interactions with the male in the clear-glass experiment affected both the time that females spent viewing males as well as female visual preferences. Results indicate that the video playback is not only useful for detecting differences between female preferences for morphological traits of male guppies, but is also much more effective in detecting preferences than the other two techniques, because it eliminates temporal variation in male behaviour.