Among mountain goats (Oreamnos americanus), females augment parental care
to enhance juvenile survival in high elevations (Festa-Bianchet et al. 1994). Male
parental care, although rare in mammals, emerges as a facultative behaviour at very
low population densities (Barash 1975) and in extreme cold, arid or seasonal
environments (Kleiman and Malcolm1981). In the dwarf hamster Phodopus
campbelli, for instance, male presence is essential to guarantee pup survival and
growth, because it alleviates female thermoregulatory stress and thus water loss due
to maternal hyperthermia, which compromises milking (Wynne-Edwards 1995,
1998). Similarly, pups of the alpine marmot Marmota marmota, due to small sizes,
have reduced thermal inertia and take advantage of the energy spent by all family
members during hibernation (‘social thermoregulation’; Arnold 1988). Young
survival, in particular, is positively associated with the number of subordinate
males, which also participate in the surveillance of the family’s territory (Arnold
1993; Allainé and Theuriau 2004).
11.5 Empirical Evidence in Plants
11.5.1 Interspecific Variation
In mountain and alpine environments, life histories are often characterised by
long-lived iteroparous perennial life cycles. A trade-off between allocation to
vegetative growth and sexual reproduction is expected as a consequence of nutrient
limitation. Thus, the increased allocation to vegetative growth should reduce the
availability of resources for reproduction (Obeso 2002). In general terms, alpine and
arctic plants invest more in maintenance and less in reproduction (Jónsdóttir 2011).
In the harsh climatic environment of high altitudes, new plant establishment is a
particularly risky (unsuccessful) mode of reproduction because of the high nutrient
demand of seed production (Watson 1984), infrequent germination and low seedling survival (Bliss 1971; Scherff et al. 1994). Accordingly, there may be a
reduction in seed rain and seed bank size as elevation increases (Molau and Larsson
2000). The demography of alpine plant populations is often characterised by low
seedling recruitment and high seedling mortality at early developmental stages
compared with lower-elevation populations (Bliss 1971; Hautier et al. 2009; Milla
et al. 2009). In general terms, this implies that the successful establishment ex-novo
of new genets (independent physiological units, or clonal colonies, sensu Watson
and Casper 1984) is infrequent. However, these paradigms regarding alpine plants
are currently changing and seedling establishment may be more common and
successful than previously thought (Jolls and Bock 1983; Chambers et al. 1990;
Forbis 2003, Forbis and Doak 2004; Giménez-Benavides et al. 2007; Venn and
Morgan 2009; Kim and Donohue 2011).
The main evidence of the rarity of seedling establishment in alpine plants is the
fact that the size-class distributions within the populations are often characterised
266
P. Laiolo and J.R. Obeso
to enhance juvenile survival in high elevations (Festa-Bianchet et al. 1994). Male
parental care, although rare in mammals, emerges as a facultative behaviour at very
low population densities (Barash 1975) and in extreme cold, arid or seasonal
environments (Kleiman and Malcolm1981). In the dwarf hamster Phodopus
campbelli, for instance, male presence is essential to guarantee pup survival and
growth, because it alleviates female thermoregulatory stress and thus water loss due
to maternal hyperthermia, which compromises milking (Wynne-Edwards 1995,
1998). Similarly, pups of the alpine marmot Marmota marmota, due to small sizes,
have reduced thermal inertia and take advantage of the energy spent by all family
members during hibernation (‘social thermoregulation’; Arnold 1988). Young
survival, in particular, is positively associated with the number of subordinate
males, which also participate in the surveillance of the family’s territory (Arnold
1993; Allainé and Theuriau 2004).
11.5 Empirical Evidence in Plants
11.5.1 Interspecific Variation
In mountain and alpine environments, life histories are often characterised by
long-lived iteroparous perennial life cycles. A trade-off between allocation to
vegetative growth and sexual reproduction is expected as a consequence of nutrient
limitation. Thus, the increased allocation to vegetative growth should reduce the
availability of resources for reproduction (Obeso 2002). In general terms, alpine and
arctic plants invest more in maintenance and less in reproduction (Jónsdóttir 2011).
In the harsh climatic environment of high altitudes, new plant establishment is a
particularly risky (unsuccessful) mode of reproduction because of the high nutrient
demand of seed production (Watson 1984), infrequent germination and low seedling survival (Bliss 1971; Scherff et al. 1994). Accordingly, there may be a
reduction in seed rain and seed bank size as elevation increases (Molau and Larsson
2000). The demography of alpine plant populations is often characterised by low
seedling recruitment and high seedling mortality at early developmental stages
compared with lower-elevation populations (Bliss 1971; Hautier et al. 2009; Milla
et al. 2009). In general terms, this implies that the successful establishment ex-novo
of new genets (independent physiological units, or clonal colonies, sensu Watson
and Casper 1984) is infrequent. However, these paradigms regarding alpine plants
are currently changing and seedling establishment may be more common and
successful than previously thought (Jolls and Bock 1983; Chambers et al. 1990;
Forbis 2003, Forbis and Doak 2004; Giménez-Benavides et al. 2007; Venn and
Morgan 2009; Kim and Donohue 2011).
The main evidence of the rarity of seedling establishment in alpine plants is the
fact that the size-class distributions within the populations are often characterised
266
P. Laiolo and J.R. Obeso