11.1 Introduction
Mountain environments present a challenge to any living organism, and elevation
gradients, with their sharp physical and ecological transitions, have been a favourite
scenario for approaching general questions about adaptive change in life histories.
Growth, development, maturation, reproduction and survival patterns of organisms
are remarkably diversified along elevation, but also tend to converge in similar
environmental conditions. Literature on the subject is abundant, but also widely
dispersed and poorly integrated with respect to the plant and animal realms, and
also between endotherms (animals that primarily produce their own heat) and
ectotherms (in which body temperature tends to match environmental temperature,
or requires behavioural thermoregulation). Undeniably, focal organisms differ in
substantial ways, but the similarities in scope, objective, and often in findings
among studies along elevation gradients provide an opportunity for a synergic
appraisal with insights from both vascular plants and animals. Here, we first
highlight those abiotic and biotic factors that are major determinants of life-history
variation in elevation. We then illustrate the primary mechanisms of evolutionary
adaptation to such variation, involving environmental and genotypic variation, their
interaction and covariation. We discuss the limitations to environmental fit within
and among species, like those imposed by intrinsic or evolutionary constraints. We
review published literature on elevation patterns in growth, reproduction and survival in populations and species of plants and animals, and discuss the elevation
life-history continuum in these taxonomic contexts. Our intention is neither to
provide an extensive survey of literature on specific taxonomic groups, which in
some cases are adequately covered (e.g. insects and birds: Hodkinson 2005; Hille
and Cooper 2015; Boyle et al. 2015), nor to perform a meta-analysis given the
literature bias towards specific taxa. Rather, we aim to provide a broad and synthetic appraisal of life-history variation along elevation. We discuss whether the
climatic and ecological shifts occurring along elevation select some strategy within
the life-history continuum and whether responses are, to a certain degree, comparable within and between unitary animals and modular plants. In spite of obvious
connections with life histories, we intentionally omit to canter on seasonality of
plant and animal life-cycle events, i.e. phenology per se, as this would require
different spatial and temporal perspectives from those adopted here.
11.2 Environmental Variation in Elevation
11.2.1 Temperature
Among the abiotic factors that vary among mountainsides, temperature is the most
critical for both plants and animals given the magnitude of variation it displays, and its
profound effect on biochemical or physiological processes (Sibly and Calow 1986).
254
P. Laiolo and J.R. Obeso
Mountain environments present a challenge to any living organism, and elevation
gradients, with their sharp physical and ecological transitions, have been a favourite
scenario for approaching general questions about adaptive change in life histories.
Growth, development, maturation, reproduction and survival patterns of organisms
are remarkably diversified along elevation, but also tend to converge in similar
environmental conditions. Literature on the subject is abundant, but also widely
dispersed and poorly integrated with respect to the plant and animal realms, and
also between endotherms (animals that primarily produce their own heat) and
ectotherms (in which body temperature tends to match environmental temperature,
or requires behavioural thermoregulation). Undeniably, focal organisms differ in
substantial ways, but the similarities in scope, objective, and often in findings
among studies along elevation gradients provide an opportunity for a synergic
appraisal with insights from both vascular plants and animals. Here, we first
highlight those abiotic and biotic factors that are major determinants of life-history
variation in elevation. We then illustrate the primary mechanisms of evolutionary
adaptation to such variation, involving environmental and genotypic variation, their
interaction and covariation. We discuss the limitations to environmental fit within
and among species, like those imposed by intrinsic or evolutionary constraints. We
review published literature on elevation patterns in growth, reproduction and survival in populations and species of plants and animals, and discuss the elevation
life-history continuum in these taxonomic contexts. Our intention is neither to
provide an extensive survey of literature on specific taxonomic groups, which in
some cases are adequately covered (e.g. insects and birds: Hodkinson 2005; Hille
and Cooper 2015; Boyle et al. 2015), nor to perform a meta-analysis given the
literature bias towards specific taxa. Rather, we aim to provide a broad and synthetic appraisal of life-history variation along elevation. We discuss whether the
climatic and ecological shifts occurring along elevation select some strategy within
the life-history continuum and whether responses are, to a certain degree, comparable within and between unitary animals and modular plants. In spite of obvious
connections with life histories, we intentionally omit to canter on seasonality of
plant and animal life-cycle events, i.e. phenology per se, as this would require
different spatial and temporal perspectives from those adopted here.
11.2 Environmental Variation in Elevation
11.2.1 Temperature
Among the abiotic factors that vary among mountainsides, temperature is the most
critical for both plants and animals given the magnitude of variation it displays, and its
profound effect on biochemical or physiological processes (Sibly and Calow 1986).
254
P. Laiolo and J.R. Obeso