Current warming and likely future impacts - Climate Change: Biological and Human Aspects - page 279

of climate change is that there is climate buffering that enables lower-altitude and
lower-latitude plants to survive, even though those at the higher-altitude and higher-
latitude end of the species' range may migrate. An example of this was provided
in 2010 by US bioscientists Daniel Doak and William Morris, of the University of
Wyoming and Duke University, respectively. They studied the climate response over
6 years of two tundra plant species, the cushion plant moss campion ( Silene acaulis )
and the geophyte alpine bistort ( Polygonum viviparum ; a geophyte is a herb with
perennating buds below the surface). Doak and Morris suggested that an analogous
situation may occur with some animal species and so explain why range shifts with
climate change are faster at higher latitudes and altitudes than at lower latitudes and
altitudes for a given species range. Nonetheless, irrespective of a climate-buffering
response, current global warming is a long-term phenomenon (in the biological as
opposed to the geological sense) and buffering will only enable species to cope with
just so much change. Ultimately, the lower-altitude and lower-latitude ends of species'
ranges will shift and the disruption of existing ecological communities could result.
The ecological consequences of variation in species responses (or rate of response)
to climate change can be particularly significant. Changes in response to climate
change at the lower trophic levels of a community (towards the bottom of the food
chain) are likely to have profound effects at higher trophic levels (towards the top).
This can happen in time (phenologically as part of the annual cycle) as well as in
space (as part of a species' range shift).
This is aptly illustrated, for example, with the results of a long-term (1958-2002)
monitoring of marine pelagic species (that is, found on middle levels or surface of
the sea) in the North Sea (Edwards and Richardson, 2004). The study looked at the
following five functional groups (with their trophic level in parentheses): diatoms
and dinoflagellates (the primary producers in this case), copepods (the secondary
producers) and non-copepod holozooplankyton (secondary and tertiary producers)
and mere plankton, including fish larvae (some of the North Sea secondary and
tertiary producers). Because the tertiary producers feed on the secondary producers,
which in turn feed on the primary producers, which photosynthesise, species in each
trophic level are dependent on the one below. As is fairly common in temperate
species, abundance varies throughout the year. Consequently, if the abundance of one
species changes at a particular time then the others would have to similarly change if
the ecosystem's structure is to remain unaltered, maintaining proportionality between
populations. Edwards and Richardson found that species responded differently over
the four-decade study period, with some species advancing their abundance peaks
and others barely changing. This mismatch in time and between trophic levels as
well as functional groups could disrupt energy/nutrient flow to the highest trophic
levels. This may explain why (in addition to fishing pressures) North Sea cod ( Gadus
morhua ) stocks have declined so markedly in recent years.
Of course, not all marine change can be attributed to climate change. Other things,
including anthropogenic factors such as fishing, affect marine ecosystems, which
is why the aforementioned North Sea study did not look at the adult commercial
species. Also note that the fishing of a few species can affect others in the ecosystem,
including those on which they feed and with which they otherwise interact. Again,
as with much climate change biology, the picture is complex and so there is often a