- Which facts contradict the classical view that sexual reproduction
in alpine plants is of reduced importance?
The proportion of species pollinated by animals does
not decrease with altitude. Relatively, alpine plants invest more in
sexual reproductive structures than lowland species. At the level of
shoots clonal plants do not reduce their effort to reproduce sexually.
- Why, in the long run, is vegetative reproduction not an alternative
to sexual reproduction in plants?
Genetic uniformity of vegetative offspring does not
allow for evolutionary adaptation to environmental changes. Seeds intimately
linked to sexual reproduction are a necessity for the colonization of
new habitats, especially in the highly fragmented alpine landscape.
- Which pollinator group becomes most frequent at highest altitudes?
Flies.
- Why are bumblebees of particular relevance for the pollination of
alpine plants?
Because they have high visitation rates, high pollen
loads, fly over large distances and at temperatures as low as 4° C.
- How do alpine plants compensate low pollination visiting rates?
By high pollen loads and long stigma receptivity.
- What has been called a "pollen risk strategy"?
Early flowering including the risk that it is too
cold for the activity of pollinators.
- Why is seed set constrained by low temperature?
Because of reduced pollen tube growth, reduced speed
of seed maturation and higher abortion rates.
- Why does life history theory predict a seed size vs. seed number "trade
off"?
Because resources for reproduction are limiting,
a tendency towards smaller seeds is always present unless selection
pressure for larger seeds is strong. An optimum seed size results from
larger seeds having an increased establishment success.
- Why are alpine seeds better dispersed by wind than seeds in the lowland?
Because of more vertical turbulance and convective
updrafts at high altitudes.
- Why are "safe sites" of particular relevance for the establishment
of seeds in alpine habitats?
Because environmental conditions like topsoil desiccation,
heat on bare soils, nighttime needle ice formation, frost heaving and
during winter cryogenic processes in the soil permit only few seedlings
to survive.
hide answers |
back
to top