r- ANDK-SELECTION REVISITED: THE ROLE OF POPULATION REGULATION IN LIFE-HISTORY EVOLUTION

Abstract

The theory of r‐ and K‐selection was one of the first predictive models for life‐history evolution. It helped to galvanize the empirical field of comparative life‐history and dominated thinking on the subject from the late 1960s through the 1970s. Large quantities of field data were collected that claimed to test predictions of the theory. By the early 1980s, sentiment about the theory had changed so completely that a proposal to test it or the use of it to interpret empirical results would likely be viewed as archaic and naïve. The theory was displaced by demographic models that concentrated on mortality patterns as the cause of life‐history evolution. Although demographic models are known for their density‐independent approach and focus on extrinsic mortality, these models can incorporate many ecological features captured by r‐ and K‐selection, such as density‐dependent population regulation, resource availability, and environmental fluctuations. We highlight the incorporation of these factors in recent theory, then show how they are manifest in our research on life‐history evolution in Trinidadian guppies (Poecilia reticulata). Explanations of the repeatable suites of life‐history differences across populations of guppies originate from demographic models of predator‐driven age‐specific mortality. Recently, careful examination of guppy demography and habitat has revealed that density‐dependent regulation and resource availability may have influenced the evolution of guppy life histories. In the field, these factors covary with predation risk; however, they can be uncoupled experimentally, providing insight into how they may have synergistically driven guppy life‐history evolution. Although life‐history theory has shifted away from a focus on r‐ and K‐selection, the themes of density‐dependent regulation, resource availability, and environmental fluctuations are integral to current demographic theory and are potentially important in any natural system.

Toward an Ecological Classification of Soil Bacteria

“…In general, rstrategists are adapted to maximize their intrinsic rate of growth when resources are abundant while K-strategists are adapted to compete and survive when populations are near carrying capacity and resources are limited (Pianka 1970). Although r-and K-selection theory is recognized as an over-simplification and it has largely been replaced with more elaborate models of life history evolution (Reznick et al 2002), the general concept is understood by all ecologists and the r-and K-categories provide a useful framework for comparing the ecological characteristics of different taxa. We expect that the concept of an r-to K-continuum should apply to both multicellular and unicellular taxa even though the specific ecological attributes used to distinguish r-and K-strategists may differ.…”

Transcriptome analysis of Haloquadratum walsbyi: vanity is but the surface

“…H. walsbyi HBSQ001, is a true halophile that under laboratory conditions grows optimally at a doubling time of about 10 days in near saturated NaCl media (3.3 M) with high concentrations of MgCl 2 (2 M) [4, 6]. In natural brines, H. walsbyi succeeds as a K -strategist, species with overall lower energy demands that are capable of efficiently utilizing a vast number of scarce resources [9, 10], in contrast to R -strategists, that are mainly fast-growing organisms adapted for high resource utilization. The essential resources for H. walsbyi are mainly provided by the main primary producer in hypersaline ecosystems, the halophilic microalgae Dunaliella salina [11].…”

Survivorship patterns in captive mammalian populations: implications for estimating population growth rates

“…Pearl (1940) expanded this classification by adding two more categories (''high-low-high'' and ''low-high-low'') to describe mammalian mortality, although as noted by Caughley (1966), there was, and arguably still is, a dearth of empirical evidence to suggest any such classification of survivorship patterns for either captive or wild mammals. Textbooks in particular frequently couch discussions of survivorship shape in the context of r vs. K selection, a dichotomy that was popular following its introduction but has more recently been criticized (as reviewed by Boyce [1984] and Reznick et al [2002]). Textbooks in particular frequently couch discussions of survivorship shape in the context of r vs. K selection, a dichotomy that was popular following its introduction but has more recently been criticized (as reviewed by Boyce [1984] and Reznick et al [2002]).…”