Geoscience Reference
In-Depth Information
hence the latitude control will be ever-present. However,
the temperature model is a terrestrial model only; it does
not apply to marine phytoplankton, which some
authorities estimate to account for two-thirds of all
photosynthesis on Earth.
(b) mean annual precipitation
y
= 3,000(1-
e
-0.000664
x
)
where
y
= NPP g m
-2
yr
-1
,
x
= mean annual precipitation
mm
, and
e
= natural log base. The Nyquist line for
precipitation follows a Mitscherlich-type growth curve.
When using such models it must not be forgotten that
NPP depends on eco-physiological processes such as
respiration, internal nutrient cycling and water use as
well as photosynthesis. Respiration declines more rapidly
than photosynthesis at higher temperatures, due to a
combination of physiological effects including thin cell
walls, closure of stomata and the death of enzymes
necessary for photosynthesis at higher temperatures.
Changes in the distribution of communities and in
species ranges
Predicted changes in the distribution of species conse-
quent on climate change fall under six categories, namely:
National Nature Reserve (NNR). Military orchid is only found at
a handful of localities in Britain, and its future survival is very
insecure under environmental change.
Photo: Michael Raw
1
Changes in the geographical ranges of species
.Many
biogeographers predict that ranges will move poleward
and uphill, that different species will move at different
speeds, and that novel communities will arise (
Plate
2
Changes in the extent of many habitats
, with different
habitats reacting differently, depending on biological
interactions such as mutualism, parasitism, predation
and competition.
3
Changes in the abundance of species
, depending on
rates of dispersal, availability of habitat, and species'
ecophysiologies; some pessimistic estimates of
extinctions are that between 15 per cent and 37 per cent
of terrestrial species will be extinct by 2050.
4
Changes in genetic diversity
, because genetic variation
is influenced by environment at both the population
and the individual level.
5
Changes in the behaviour of migratory species
, and in the
location of breeding and over-wintering areas.
6
Changes in susceptibility to invasion
by non-native
species.
Plate 28.11
Walrus are sea-bed (benthic) feeders on clams,
beneficial to them.
Photo: Canadian Wildlife Service
In mountainous regions research has also been
conducted on vegetation changes consequent on climate
change. Biome-scale modelling in the Rocky Mountains
