other reproductive features, such as eggshell thickness and clutch size, both
decreasing with the degree of viviparity and elevation (Mathies and Andrews
1995). Moreover, pregnant females pay metabolic costs for maintaining higher
body temperatures, as visibly appreciable in postpartum body condition. However,
the ultimate consequences for survival depend upon a combination of factors, from
stored reserves and thermal conditions to the capability of using current food intake
during reproduction (Lourdais et al. 2002; Cox et al. 2010). Many reptiles are in
fact predominant ‘capital breeders’, i.e. they use reserves gathered over long
periods prior to the year of reproduction, but nevertheless are able to optionally
integrate energy from current feeding (‘income’) (Shine 2005).
In oviparous species, a decrease in clutch size translates into an increase in
offspring size (Sinervo et al. 1992), infrequent reproduction (Shine 2005) and
enhanced annual survival rate (Adolph and Porter 1993). Lizards exhibit indeterminate and fully plastic growth (Sears and Angilletta 2003) with a few documented
cases of countergradient variation (Sinervo 1990). Although no comparative analyses have addressed interspecific variation along elevation gradients, a trend for
‘slow’ life strategies in cold-environment or slow-metabolism taxa, in contrast to
‘fast’ strategies in hot-environment or fast-metabolism taxa, has been highlighted
(Bauwens and Díaz-Uriarte 1997; Shine 2005).
11.4.5 Birds
Several comparative reviews on avian intra- and interspecific patterns highlight a
strategy of reduced annual fecundity, e.g. reduced clutch size or reproductive
attempts per year, with elevation. As an opposite pattern, the duration of the
incubation and nesting phases increase with elevation (Krementz and
Handford1984; Badyaev 1997a; Badyaev and Ghalambor 2001; Boyle et al. 2015;
Hille and Cooper 2015; Laiolo et al. 2015b). Ruling out the effect of body size, low
predation pressures and poor food availability likely contribute to prolonged parental care, as a result of bird parents spending increasingly longer periods outside
the nest (Boersma 1982). This fact inevitably slows the development of young, but
protects parental survival (Martin 2002) and improves food provisioning where
resources are scarce and scattered and where chicks have increased metabolic
demands because of cold weather.
At the intraspecific level, survival has been shown to increase with elevation in
some study cases (e.g. Bears et al. 2009), but pairwise comparisons of closely
related species, subspecies or populations are not conclusive in this respect
(Badyaev and Ghalambor 2001; Boyle et al. 2015). It is possible that large variations in extrinsic (environmental) mortality, essentially independent of the choices
made by individuals, override slight differences in intrinsic mortality between
entities with a great degree of shared history. Tests with phylogenetically and
functionally diverse bird assemblages indeed suggest remarkable variation in survival patterns (Laiolo et al. 2015b; Bastianelli et al. 2017).
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P. Laiolo and J.R. Obeso
decreasing with the degree of viviparity and elevation (Mathies and Andrews
1995). Moreover, pregnant females pay metabolic costs for maintaining higher
body temperatures, as visibly appreciable in postpartum body condition. However,
the ultimate consequences for survival depend upon a combination of factors, from
stored reserves and thermal conditions to the capability of using current food intake
during reproduction (Lourdais et al. 2002; Cox et al. 2010). Many reptiles are in
fact predominant ‘capital breeders’, i.e. they use reserves gathered over long
periods prior to the year of reproduction, but nevertheless are able to optionally
integrate energy from current feeding (‘income’) (Shine 2005).
In oviparous species, a decrease in clutch size translates into an increase in
offspring size (Sinervo et al. 1992), infrequent reproduction (Shine 2005) and
enhanced annual survival rate (Adolph and Porter 1993). Lizards exhibit indeterminate and fully plastic growth (Sears and Angilletta 2003) with a few documented
cases of countergradient variation (Sinervo 1990). Although no comparative analyses have addressed interspecific variation along elevation gradients, a trend for
‘slow’ life strategies in cold-environment or slow-metabolism taxa, in contrast to
‘fast’ strategies in hot-environment or fast-metabolism taxa, has been highlighted
(Bauwens and Díaz-Uriarte 1997; Shine 2005).
11.4.5 Birds
Several comparative reviews on avian intra- and interspecific patterns highlight a
strategy of reduced annual fecundity, e.g. reduced clutch size or reproductive
attempts per year, with elevation. As an opposite pattern, the duration of the
incubation and nesting phases increase with elevation (Krementz and
Handford1984; Badyaev 1997a; Badyaev and Ghalambor 2001; Boyle et al. 2015;
Hille and Cooper 2015; Laiolo et al. 2015b). Ruling out the effect of body size, low
predation pressures and poor food availability likely contribute to prolonged parental care, as a result of bird parents spending increasingly longer periods outside
the nest (Boersma 1982). This fact inevitably slows the development of young, but
protects parental survival (Martin 2002) and improves food provisioning where
resources are scarce and scattered and where chicks have increased metabolic
demands because of cold weather.
At the intraspecific level, survival has been shown to increase with elevation in
some study cases (e.g. Bears et al. 2009), but pairwise comparisons of closely
related species, subspecies or populations are not conclusive in this respect
(Badyaev and Ghalambor 2001; Boyle et al. 2015). It is possible that large variations in extrinsic (environmental) mortality, essentially independent of the choices
made by individuals, override slight differences in intrinsic mortality between
entities with a great degree of shared history. Tests with phylogenetically and
functionally diverse bird assemblages indeed suggest remarkable variation in survival patterns (Laiolo et al. 2015b; Bastianelli et al. 2017).
264
P. Laiolo and J.R. Obeso