The Evolutionary Ecology of Life History Variation in the Garter Snake Thamnophis elegans

Ecology ◽  
1999 ◽  
Vol 80 (7) ◽  
pp. 2314 ◽  
Author(s):  
Anne M. Bronikowski ◽  
Stevan J. Arnold
Keyword(s):  
Life History ◽  
Evolutionary Ecology ◽  
Garter Snake ◽  
Life History Variation ◽  
Thamnophis Elegans

scholarly journals Density Dependence, Evolutionary Optimization, and the Diversification of Avian Life Histories

The Condor ◽  
2000 ◽  
Vol 102 (1) ◽  
pp. 9-22 ◽  
Author(s):  
Robert E. Ricklefs
Keyword(s):  
Life History ◽  
Life Table ◽  
Life Histories ◽  
Life History Traits ◽  
Evolutionary Ecology ◽  
Reproductive Rate ◽  
Empirical Modeling ◽  
Adult Survival ◽  
Life History Variation ◽  
Evolutionary Response

Abstract Although we have learned much about avian life histories during the 50 years since the seminal publications of David Lack, Alexander Skutch, and Reginald Moreau, we still do not have adequate explanations for some of the basic patterns of variation in life-history traits among birds. In part, this reflects two consequences of the predominance of evolutionary ecology thinking during the past three decades. First, by blurring the distinction between life-history traits and life-table variables, we have tended to divorce life histories from their environmental context, which forms the link between the life history and the life table. Second, by emphasizing constrained evolutionary responses to selective factors, we have set aside alternative explanations for observed correlations among life-history traits and life-table variables. Density-dependent feedback and independent evolutionary response to correlated aspects of the environment also may link traits through different mechanisms. Additionally, in some cases we have failed to evaluate quantitatively ideas that are compelling qualitatively, ignored or explained away relevant empirical data, and neglected logical implications of certain compelling ideas. Comparative analysis of avian life histories shows that species are distributed along a dominant slow-fast axis. Furthermore, among birds, annual reproductive rate and adult mortality are directly proportional to each other, requiring that pre-reproductive survival is approximately constant. This further implies that age at maturity increases dramatically with increasing adult survival rate. The significance of these correlations is obscure, particularly because survival and reproductive rates at each age include the effects of many life-history traits. For example, reproductive rate is determined by clutch size, nesting success, season length, and nest-cycle length, each of which represents the outcome of many different interactions of an individual's life-history traits with its environment. Resolution of the most basic issues raised by patterns of life histories clearly will require innovative empirical, modeling, and experimental approaches. However, the most fundamental change required at this time is a broadening of the evolutionary ecology paradigm to include a variety of alternative mechanisms for generating patterns of life-history variation.

scholarly journals Evolutionary ecology of endocrine-mediated life-history variation in the garter snakeThamnophis elegans

Ecology ◽  
2009 ◽  
Vol 90 (3) ◽  
pp. 720-728 ◽  
Author(s):  
Amanda M. Sparkman ◽  
Carol M. Vleck ◽  
Anne M. Bronikowski
Keyword(s):  
Life History ◽  
Evolutionary Ecology ◽  
Life History Variation

scholarly journals An empirical test of evolutionary theories for reproductive senescence and reproductive effort in the garter snake Thamnophis elegans

2007 ◽  
Vol 274 (1612) ◽  
pp. 943-950 ◽  
Author(s):  
Amanda M Sparkman ◽  
Stevan J Arnold ◽  
Anne M Bronikowski
Keyword(s):  
Life History ◽  
Reproductive Effort ◽  
Empirical Test ◽  
Reproductive Failure ◽  
Fast Growth ◽  
Garter Snake ◽  
Evolutionary Divergence ◽  
Reproductive Senescence ◽  
The Difference ◽  
Thamnophis Elegans

Evolutionary theory predicts that differential reproductive effort and rate of reproductive senescence will evolve under different rates of external mortality. We examine the evolutionary divergence of age-specific reproduction in two life-history ecotypes of the western terrestrial garter snake, Thamnophis elegans . We test for the signature of reproductive senescence (decreasing fecundity with age) and increasing reproductive effort with age (increasing reproductive productivity per gram female) in replicate populations of two life-history ecotypes: snakes that grow fast, mature young and have shorter lifespans, and snakes that grow slow, mature late and have long lives. The difference between life-history ecotypes is due to genetic divergence in growth rate. We find (i) reproductive success (live litter mass) increases with age in both ecotypes, but does so more rapidly in the fast-growth ecotype, (ii) reproductive failure increases with age in both ecotypes, but the proportion of reproductive failure to total reproductive output remains invariant, and (iii) reproductive effort remains constant in fast-growth individuals with age, but declines in slow-growth individuals. This illustration of increasing fecundity with age, even at the latest ages, deviates from standard expectations for reproductive senescence, as does the lack of increases in reproductive effort. We discuss our findings in light of recent theories regarding the phenomenon of increased reproduction throughout life in organisms with indeterminate growth and its potential to offset theoretical expectations for the ubiquity of senescence.

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