Alexandra Rose

Alexandra (Alex) Rose is interested in exploring patterns in avian clutch size. In particular, her dissertation research is focused on understanding to what extent avian taxa show a latitudinal gradient in clutch size and the potential role for day length to explain that pattern. She is using three complementary approaches to addressing her questions about clutch size: a synthetic review of clutch size gradients in North American birds; a bio-energetic model of the relationship of clutch size to day length; and a comparative field study of Tree swallow populations in California and Alaska .

Alex joined the Lyon lab in 2005. She has a diverse background in ecological research and has done field work with raptors, seabirds and songbirds as well as small mammals and white-tailed deer. For more details, see her C.V.

Dissertation Work:

The focus of my research is one of the most striking and puzzling patterns in the field of ecology--the latitudinal gradient in avian clutch size. This pattern describes the observation that populations of bird species that breed at high latitudes tend to lay more eggs in a nesting attempt than populations of the same species that breed closer to the equator. This pattern is displayed by an impressive diversity of bird taxa across both hemispheres (Lack 1947) . And yet, the relative simplicity of the pattern is contrasted by how complicated the search for an explanation of the pattern has been; many different explanations have been proposed and rejected since David Lack described it in his classic 1947 series of monographs in the Ibis. Lack originally proposed that the cline in clutch size could be explained by latitudinal changes in day length. This intuitively appealing hypothesis proposes that birds at high latitudes have more hours in a day to forage and can therefore provision more offspring than birds at lower latitudes. This explanation was soon rejected—prematurely, in my opinion--in favor of more complicated explanations (e.g. seasonality of resources (Ricklefs 1980) , nest predation (Skutch 1949) , adult mortality (Cody 1971) , constraints on egg physiology (Cooper et al. 2005) , and various life-history trade-offs (Cody 1966) ). While a number of studies have shown that these ecological interactions explain some of the observed variation in clutch size (e.g. Martin et al. 2000, Ghalambor and Martin 2001, Martin et al. 2001) , none have been conclusive.

I am carefully testing the original idea that day length is a critical force generating this pervasive life history pattern. The apparent reason for Lack's rejection of day length as a causal factor for clutch size patterns is clearly erroneous, based on a lack of recognition of the maintenance costs for parents and of the possibility of nonlinear effects of daylight across latitudes (Hussell 1985) . Surprisingly, there appears to be only a few experimental tests of the day length hypothesis, and all of these high-latitude studies seem to support the day length hypothesis (e.g. Hussell 1972) .

My dissertation research is aimed at exploring to what extent the amount of daylight during the breeding season does matter for birds and in what way. I am using three complementary approaches to evaluate the causal factors driving clutch size variance. First, I am in the process of using nest card records from the Cornell Lab of Ornithology, and other sources, to conduct a large, comparative analysis of clutch size in a diversity of avian taxa and guilds from tropical to arctic latitudes. The purpose of this project is to quantify which birds actually demonstrate a clutch size gradient, what the shape and strength of the relationship of clutch size to latitude is for different species, and how well ecological factors such as guild and nesting habitat predict the clutch size gradient for a given species. Second, I am using a bio-energetics approach to modeling how day length translates into foraging success and nestling growth, allowing a quantitative prediction of day length effects on clutch size that can be tested with my data. Third, I am performing a two year comparative study in California and Alaska of two breeding populations of Tree Swallows. The purpose of this part of my work is to test whether differences in day length translate into differences in how breeding birds provision their young across latitudinal gradients. While many of the hypotheses for clutch size patterns, such as food limitation and predation risk, have been tested experimentally via comparisons of tropical and temperate populations (e.g. Martin et al. 2000, e.g. Ghalambor and Martin 2001) , I am performing a comparative study across a large latitudinal gradient within the temperate zone.

WORKS CITED

 

Cody, M. L. 1966. A general theory of clutch size. Evolution 20 :174-184.

Cody, M. L. 1971. Ecological aspects of reproduction. Pages 461-512 in D. S. Farner and J. R. King, editors. Avian Biology. Academic Press, New York.

Cooper, C. B., W. M. Hochachka, G. Butcher, and A. A. Dhondt. 2005. Seasonal and latitudinal trends in clutch size: Thermal constraints during laying and incubation. Ecology 86 :2018-2031.

Ghalambor, C. K., and T. E. Martin. 2001. Fecundity-survival trade-offs and parental risk-taking in birds. Science 292 :494-497.

Hussell, D. J. T. 1972. Factors Affecting Clutch Size in Arctic Passerines. Ecological Monographs 42 :317-364.

Hussell, D. J. T. 1985. Clutch Size, Daylength, and Seasonality of Resources - Comments on Ashmole Hypothesis. Auk 102 :632-634.

Lack, D. 1947. The significance of clutch-size, parts 1 and 2. Ibis 89 :302-352.

Martin, T. E., P. R. Martin, C. R. Olson, B. J. Heidinger, and J. J. Fontaine. 2000. Parental care and clutch sizes in North and South American birds. Science 287 :1482-1485.

Martin, T. E., A. P. Moller, S. Merino, and J. Clobert. 2001. Does clutch size evolve in response to parasites and immunocompetence? Proceedings of the National Academy of Sciences of the United States of America 98 :2071-2076.

Ricklefs, R. E. 1980. Geographical Variation in Clutch Size among Passerine Birds - Ashmoles Hypothesis. Auk 97 :38-49.

Skutch, A. F. 1949. Do tropical birds rear as many young as they can nourish? Ibis 91 :430-455.