Geology Reference
In-Depth Information
Species on the Move
Perhaps the clearest evidence that climate change is a reality comes from what is hap-
pening to the world's biotic communities, which are being affected around the world in
a variety of alarming ways. There are changes in phenology, which refers to the study of
the timing of key events in the world of living beings, such the precise dates and seasons
of flowering or egg laying. Then there are changes in the overall distribution of species,
including whether their overall ranges are expanding or contracting. Next are changes
to the composition of biotic communities, and in the interactions between these species.
Lastly there is concern about changes to the overall functioning of whole ecosystems,
and the impacts on the 'ecosystem services' they give us.
In the temperate regions of the world, spring-time events such as flowering, budding,
singing, spawning, migrant arrival and insect appearances are not what they used to
be—they have all been happening progressively earlier since the 1960s. In Britain alone,
16% of flowering plants flowered significantly earlier during the 1990s compared to
previous decades, and similar trends are being noted all over the world. There are also
changes to some key autumnal events, such as amongst some migratory birds, which
have abandoned winter migration altogether, or have delayed their departures.
Each species has its own very specific range of tolerance for temperature and mois-
ture, and species move in an attempt to live within their comfort zones as the climate
changes. The general trend in a recent study of 1700 species is a poleward movement
of 6.1 kilometres per decade, and a 6.1 metres movement up the sides of mountains.
Virtually the whole biosphere is being uprooted in unprecedented ways. Examples are
legion, including the northward march of the boreal forest at the expense of open tundra
vegetation; the northwards expansion of red foxes in Arctic Canada and the simultan-
eous shrinking in the range of the Arctic fox; the upward movements of alpine plants in
the European Alps by 1-4 metres per decade; the increasing abundance of warm-water
species amongst the zooplankton, fish and intertidal invertebrates in the North Atlantic
and along the coasts of California; and the extension of lowland Costa Rican birds into
higher areas from lower mountain slopes, because of changes in the frequency of dry
season mist. Butterflies, too, are being disturbed (they respond very quickly to climate
change); in Britain and North America, 39 butterfly species have moved northwards by
up to 200 kilometres in 27 years.
But many of these exiled species face another danger—habitat fragmentation. As
economic growth and development proceed apace, more and more of Gaia's wild places
are paved over, built on, or ploughed up for intensive agriculture, preventing species
that need to move to higher latitudes and altitudes from reaching suitable safe havens.
