Past climates: Why the rate of change matters
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Plants and animals are adapted to their environment. When climate changes slowly, they can migrate to follow the conditions that suit them. But when climate changes quickly, plant populations sometimes can’t migrate fast enough and can be damaged before they have time to spread. This also impacts on animal populations which rely on vegetation for food and shelter.
Migration of plants and trees
Unlike animals, plants, trees and other vegetation grow fixed in one place. Except in cases of human intervention, plant populations can only migrate across successive generations, as new populations grow in new locations. Seed dispersal can be airborne or seeds can be spread by animals and insects. Although seeds can travel far and wide, there are limits to the distance and speed of dispersal. Gradual changes in climate tend to allow new populations time to establish themselves. More rapid changes can damage the new plants before they have time to grow and reproduce.
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Trees and other vegetation need successive generations to migrate
Image: Mei Teng / RGB Stock
Animal migration
Animal and insect populations can migrate far more swiftly than vegetation can. Animals don’t have to wait for the next generation to grow up – they can simply walk, swim or fly to a new location. But animal populations rely on plants and trees to provide a suitable habitat. Many animals are capable of adapting to new conditions and new types of habitat, but damage to large areas of vegetation can put pressure on local animal populations, as many creatures compete to find enough food and shelter in a reduced space. Because of this dependency on vegetation, animals as well as plants can be vulnerable to climate change.
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Birds and other animals can migrate swiftly but need vegetation for food and shelter
Image: Andreas Trepte / creativecommons.org
Obstacles to migration
Obstacles such as mountain ranges, large areas of water or, more recently, human infrastructure can hinder the migration of plant and animal species. This can affect seasonal migrations as well as long-term population movements. Many species travel long distances each year to follow favourable seasonal climate conditions, but fragmentation of habitats or barriers along migration routes can make it harder for migrating populations to reach their destination. Plants and animals migrating in response to long-term climate changes also need viable migration pathways. The more obstacles that are present, the more difficult it is for species to move to new areas if local climate conditions become unfavourable.
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A mountain range in Alaska, North America
Image: SXC / Onixxino
Seasonal environmental variations
Seasonal changes in temperature and rainfall cause some regions to switch from warm to freezing – or wet to dry – conditions over just a few months. Yet these changes don’t have large-scale impacts on ecosystems, because plants and animals are accustomed to the yearly variations and have evolved to cope with them. Some species temporarily migrate, while others hibernate until the following year. Even a few years of unusually hot or cold conditions won’t usually pose a problem for natural systems. Environmental changes tend to have significant impact on plants, animals and ecosystems only when the changes are sustained over many years or decades.
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A tree photographed in different seasons
Image: Mike Kiev / Fotolia
Adaptation and evolution
Plants and animals are usually well suited to the climates they live in, so changes in their environment can require migration, adaptation or both. Gradual changes are usually easier to adapt to than abrupt shifts in conditions, although both can prompt adaptation. If a change in climate persists for long enough, new species can evolve. In one example, scientists think a number of brown bears may have become isolated in the Arctic. Over successive generations, the bears developed characteristics better suited to their icy environment, such as lighter fur, eventually becoming a new species – polar bears.
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A leaf insect that has evolved to use camouflage to hide from predators
Image: smjet / RGB Stock
Winners and losers
Shifts in climate create both winners and losers, as diverse species respond differently to the changes. For example, the dinosaurs – which had dominated the Earth for nearly 200 million years – died out 65 million years ago in a ‘mass extinction’ which scientists think was caused by rapid climate change. But the ancestors of modern mammal species survived and eventually prospered. Because mammals were very small at the time, they needed less food to survive than the larger dinosaurs and tended to live in underground burrows where they could shelter from extremes of weather on the surface. Over time, mammals grew both in size and in number – today there are more than 5000 species.
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Artist's impression of some of the dinosaurs that walked the Earth millions of years ago
Image: AlienCat / Fotolia
Profile: Dr. Minna Valiranta
Surviving helicopter fires and snowmobile crashes is all in a day’s work for Minna Valiranta in her efforts to learn how the climate has changed over the past 100,000 years. ‘My work involves collecting and identifying plant remains from sediment cores to help reconstruct past environmental conditions.’ Collecting these sediment cores from the Arctic is tricky work but has revealed surprising information about the vegetation that existed during ice-free periods. ‘By looking at old sediment layers we’ve discovered that trees grew in northern Finland around 90,000 years ago. The traditional view had been that this area was covered by tundra or ice. Our research completely changed this view.’
