Thus, low-elevation semelparous populations depended primarily on seedling
recruitment and precocious reproduction, whereas alpine plants tended to be iteroparous and to produce more vegetative rosettes. These results showed an altitudinal variation in parity (number of reproductive events), and its demographic
consequences, indicating that plastic or evolutionary changes in this trait have a
clear influence on population performance along altitudinal gradients.
As the allocation of resources to reproduction results in a reduction of allocation
to vegetative growth and, therefore, an impact on future reproductive success, the
trade-off between allocation to reproduction and vegetative growth is also a
determinant of iteroparous perennial cycles within species. Hautier et al. (2009)
conducted a transplant experiment to assess the influence of both the altitudinal
origin of populations and the altitude of the growing site on vegetative growth and
reproductive investment in Poa alpina. According to the general trend in plants, the
variation in reproductive investment was mainly explained by plant size. However,
the vegetative growth and the relative reproductive allocation decreased in populations originating from higher altitudes compared to populations originating from
lower altitudes. They also found that the importance of plasticity was scarce in
relation to genetic effects and interpreted these results as a consequence of local
adaptations.
Gao-Lin et al. (2011) tested the hypothesis that seed mass was positively correlated with altitude within species in four congeneric Saussurea (Asteraceae) that
occur in the Tibetan Plateau. They found a general trend of a significant increase in
seed mass with altitude. Contrarily, Meng et al. (2014) showed that along an
altitudinal gradient in the Hengduan Mountains, mean seed weight of
Sinopodophyllum hexandrum decreased significantly. Pluess et al. (2005) compared
seed weights among populations of four species from different habitats and with
different life histories along an altitude gradient (Scabiosa lucida, Saxifraga
oppositifolia, Epilobium fleischeri and Carex flacca). In all the four species, they
found no indication for heavier seeds at higher altitudes. Similarly, in the cactus
Gymnocalycium monvillei seedling height increased with altitude, whereas seed
mass was not related to this variable (Bauk et al. 2015).
Assessing adaptive differentiation of plant populations along altitude gradients is
useful for predicting how they may respond to climatic change. Local adaptation
along altitudinal gradients has been demonstrated in several alpine plant species
after reciprocal transplant experiments (Byars et al. 2007; Kim and Donohue 2013;
Toräng et al. 2015) or transplants to a common garden (Stenström et al. 2002).
However, information about local adaptation in traits related directly to life history
is still scarce. Leimu and Fischer (2008) reviewed the information about local
adaptations and found that although local plants performed better than foreign
plants in 71% of the studies, local adaptation, sensu stricto, was demonstrated in
approximately 40% of the case studies.
Surprisingly, genetic diversity of alpine plant populations is not as depleted
as predicted from small population sizes and repeated vegetative multiplication,
270
P. Laiolo and J.R. Obeso
recruitment and precocious reproduction, whereas alpine plants tended to be iteroparous and to produce more vegetative rosettes. These results showed an altitudinal variation in parity (number of reproductive events), and its demographic
consequences, indicating that plastic or evolutionary changes in this trait have a
clear influence on population performance along altitudinal gradients.
As the allocation of resources to reproduction results in a reduction of allocation
to vegetative growth and, therefore, an impact on future reproductive success, the
trade-off between allocation to reproduction and vegetative growth is also a
determinant of iteroparous perennial cycles within species. Hautier et al. (2009)
conducted a transplant experiment to assess the influence of both the altitudinal
origin of populations and the altitude of the growing site on vegetative growth and
reproductive investment in Poa alpina. According to the general trend in plants, the
variation in reproductive investment was mainly explained by plant size. However,
the vegetative growth and the relative reproductive allocation decreased in populations originating from higher altitudes compared to populations originating from
lower altitudes. They also found that the importance of plasticity was scarce in
relation to genetic effects and interpreted these results as a consequence of local
adaptations.
Gao-Lin et al. (2011) tested the hypothesis that seed mass was positively correlated with altitude within species in four congeneric Saussurea (Asteraceae) that
occur in the Tibetan Plateau. They found a general trend of a significant increase in
seed mass with altitude. Contrarily, Meng et al. (2014) showed that along an
altitudinal gradient in the Hengduan Mountains, mean seed weight of
Sinopodophyllum hexandrum decreased significantly. Pluess et al. (2005) compared
seed weights among populations of four species from different habitats and with
different life histories along an altitude gradient (Scabiosa lucida, Saxifraga
oppositifolia, Epilobium fleischeri and Carex flacca). In all the four species, they
found no indication for heavier seeds at higher altitudes. Similarly, in the cactus
Gymnocalycium monvillei seedling height increased with altitude, whereas seed
mass was not related to this variable (Bauk et al. 2015).
Assessing adaptive differentiation of plant populations along altitude gradients is
useful for predicting how they may respond to climatic change. Local adaptation
along altitudinal gradients has been demonstrated in several alpine plant species
after reciprocal transplant experiments (Byars et al. 2007; Kim and Donohue 2013;
Toräng et al. 2015) or transplants to a common garden (Stenström et al. 2002).
However, information about local adaptation in traits related directly to life history
is still scarce. Leimu and Fischer (2008) reviewed the information about local
adaptations and found that although local plants performed better than foreign
plants in 71% of the studies, local adaptation, sensu stricto, was demonstrated in
approximately 40% of the case studies.
Surprisingly, genetic diversity of alpine plant populations is not as depleted
as predicted from small population sizes and repeated vegetative multiplication,
270
P. Laiolo and J.R. Obeso