Articles
Reproductive fitness, the probability that an individual will produce viable offspring of equal or greater replacement value, provides an avenue by which environmental influences on individuals transcend to population and higher-order phenomena. Life history strategies represent the suite of traits that optimize reproductive fitness of individuals within the environmental and phylogenetic constraints imposed on the species during its evolutionary history. A species' life history strategy is shaped by trade-offs among alternative, attainable expressions of traits, including (but not limited to) life span; time to maturation; number of lifetime breeding events; and parental investment in offspring number, size or energy content, or care (Stearns 1989, Congdon et al. 2001. The combination of traits and the specific expressions that optimize fitness are unique to a species, yet have classically been broadly categorized as "r-selected" or "K-selected" life history strategies (Pianka 1970). While these categorizations represent theoretical extremes bounding a vast diversity of trait combinations found in nature, and thus no realized life history strategy represents an "ideal" r-or K-selected strategy, the categorizations are conceptually useful for broadly assessing potential environmental influences on fitness resulting from a particular life history strategy.Species that possess r-selected strategies tend to be opportunistic, short-lived, rapid to mature, and semelparous (breeding only once), producing large numbers of small offspring. Such species typically exploit rapidly changing environmental conditions and are capable of establishing populations quickly in novel environments (Pianka 1970). Relative to r-selected species, those employing K-selected life history strategies are long-lived, slow to mature, iteroparous (breeding multiple times), and typically make large per capita parental investments in few offspring during a given breeding event (Pianka 1970). This life history strategy is optimized for environmental conditions that on average are relatively stable over an individual's long reproductive lifetime, yet it is resilient to periodic, stochastic fluctuations in habitat quality that may compromise a given breeding event (a "bet-hedging" strategy; Stearns 1976).Persistent, synthetic contaminants were developed and have been used widely only in the past century, yet already their use has resulted in contamination of habitats on a global scale (e.g., Schwarzenbach et al. 2006). Synthetic compounds such as organochlorine pesticides, polychlorinated biphenyls (PCBs), and brominated fire retardants (brominated diphenyl ethers, or BDEs) can persist in the environment for decades, Christopher L. Rowe (e-mail: rowe@cbl.umces.edu