Page 641 - Geosystems An Introduction to Physical Geography 4th Canadian Edition

Species’ Distributions Shift with Climate Change
An ecosystem involves plants and ani- mals and their interactions with the physical environment. Changing cli- mate affects ecosystems because temper- ature and moisture are among the physical limiting factors on species distributions and ecosystem function. either through a lack or through an excess, such factors limit biotic operations. Species are able to toler- ate varying conditions for each limiting fac- tor, but if conditions become too difficult, species must adapt or evolve, seek new habitat elsewhere, or become extinct.
as temperatures increase, many ani- mals are expanding their ranges to higher latitude areas with more favorable thermal conditions. also, species are expanding their ranges to higher elevations—but existing high-elevation species are losing available range as temperatures increase. Shifting climatic conditions may exceed the rate at which some species can mi- grate, causing a contraction in suitable ranges at lower latitudes or elevations.
Changing climate in northern Canada is impacting the ranges of many spe- cies. narwhals and beluga whales that inhabit cold arctic waters face changed oceanographic conditions. reduced sea ice will limit the opportunities for polar bears to access a principal food source— seals. Under a 4 C° increase in the col- lared lemming’s territory—a keystone species in the food chain—a study pre- dicted its range would decline by about 305 000 km2, or 60%. Facing competition for habitat and resources from southern migrants, a number of species might be able to accommodate shifting their ranges further north, only to find that ex- pansion limited by the arctic Ocean.
a relatively long-term study in yosem- ite national Park, California, found that over the last half century, small mammal communities moved to higher elevations in response to warming temperatures. Scientists found that half the species monitored showed substantial move- ment toward cooler temperatures at higher elevations, which is consistent with a 3 C° increase in minimum temperature during the last century (Figure gn 19.1).
Formerly low-elevation species ex- panded their ranges, and high-elevation species contracted their ranges. These animals are highly threatened by climate
change. Because the latitudinal tem- perature gradient in the tropics is slight, tropical species are similarly at risk of mountain-top extinction as warming pushes climatically suitable conditions beyond the reaches of mountain peaks.
expansions of insect populations are having dramatic effects on ecosystems and human health in Canada. For exam- ple, the range of mountain pine beetle has expanded from the interior of British Columbia with warmer winter tempera- tures at higher elevations and higher lati- tudes. So far this has devastated forests in British Columbia and yukon. now that the range of mountain pine beetle has crossed over the Continental Divide into alberta, there is concern for pine trees in boreal forests across Canada, particularly if the predicted further warming occurs. Human health is being impacted by the northerly spread of disease-carrying ticks. lyme disease, for example, is spreading northward and eastward into Ontario, Québec, and the Maritimes.
global climate change is expected to affect forest distributions as well, although plant communities are slower to respond to environmental change. a recent study of 130 species of north american
trees suggests that ranges will
shift northward between 330 and
700 km, depending on the suc-
cess of dispersal into new habitats.
Thus, deciduous forests that are
now common in the United States
would be found in Canada by cen-
tury’s end, and the present range
would be replaced by grasslands in
some areas and by a different mix
of tree species in other regions.
Figure gn 19.2 shows a projected northward shift in the climatic envelope for one species, sugar maple, in eastern north america.
Working group iii in the 2014 intergovernmental Panel on Cli- mate Change, Fifth Assessment Report estimated with “high confidence,” that a warming of 1 C° to 2 C° produces a “... large fraction of terrestrial and fresh- water species face increased extinction rates,” and that many terrestrial, freshwater, and ma- rine species have already shifted
500
500
▲Figure GN 19.2 Projected climatic shift in range of sugar maple. Current and projected future range of sugar maple (Acer saccharum) based on the conditions for 2071–2100 modelled by the Canadian Centre for Climate Modelling and analysis. [reprinted by permission of University of California Press. BioScience 57:929–937, D. W. Mckenney, J. H. Pedlar,
k. lawrence, k. Campbell, and M. F. Hutchinson,
Beyond Traditional Hardiness Zones: Using Climate Envelopes to Map Plant Range Limits. © 2007.]
0 km
0 miles
now
▲Figure GN 19.1 Montane species relocate in response to climate change. Species are moving to higher elevations in the Southern and Central Sierra nevada as their preferred ranges shift to the higher mountains in the background. [robert Christopherson.]
their geographic ranges in response to climate change. For species to survive, they must adapt or evolve, or continue to shift to stay within their ranges. Thus, a physical geography text written 20 to 70 years from now may have to redo the biome maps to reflect these changes in species distributions. in this chapter, we discuss ecosystems and limiting factors; biomes are the focus of Chapter 20.
Future Climate Range Current Climate Range
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