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There is a huge variety of mammal species living
in different types of forests. They range from the tiny, mouse-like shrews scurrying along the forest floor, to acrobatic
primates in tropical rainforests. Many forest mammals are excellent climbers, and make use of trees for food, shelter, and travel routes.
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Mammals are often nocturnal, and almost all have a fear of humans, which makes them difficult to observe. Forest mammals are shy and difficult to view, even in the tropical rainforests where they are most abundant. Large mammals require a larger territory, and therefore fewer of these mammals can share any given amount of forest. |
Monkeys are some of the most common arboreal mammals, with several dozen species in the tropical Americas alone. Not all monkeys are large and easy to spot, however: the marmosets are some of the world's smallest primates, and the pygmy marmoset weighs only 3 ounces (185 grams). |
Squirrels are common throughout North American temperate and boreal forests. Photo by Maya Walters. |
Because of their bone structure, mammals fossilize easily, which means their evolution is better understood than that of other animals. When mammals first started to become a common and dominant type of animal, the continents of Europe, Asia, Africa, and North America were all linked by land bridges, creating a "World Continent". The mammals that evolved on this World Continent were therefore fairly closely related. South America and Australia, however, were not joined to this World Continent, so three distinct populations of mammals eventually developed: the Australian mammals, the South American mammals, and the mammals of the World Continent. |
| Many similar habitats and ecological niches existed on all of the three continents. This led to many unrelated species evolving in similar ways--examples of convergent evolution. When North and South America were connected by Central American landforms, animals were able to expand their ranges onto a whole new continent. Many animals weren't successful in moving from one continent to the other, but others completely took over ecological niches that had previously belonged to mammals that had evolved on that continent. Early monkey-like primates gradually migrated to South America, where they evolved into the spider monkeys, howler monkeys, and the other prehensile-tailed primates which now inhabit the tropical forest canopies. | There are fewer than 5,000 species of mammals but the diversity of shapes and behaviors is astonishing. Most of these species have been studied more than any other class of animals. |
| Monkeys are social, commonly moving in troops which can number over 30 individuals. Some monkeys forage exclusively for leaves and fruits, and large groups often spend several hours feeding in a single rainforest tree. Other species also hunt for small mammals and birds. The capuchin monkeys of Central America feed on palm nuts, and are important in seed dispersal. They also eat the grubs of certain parasitic beetles which damage trees. | The diet of a spider monkey is made up of approximately 80% fruits and 20% leaves. |
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 Gorillas are some of the largest primates, and live on the forest floor. Like monkeys, they live in social groups. Photo by Maya Walters. |
They build dams, shape streams and riparian zones, change water flow, help determine the success of tree species, create vital habitat for other animals, and are an integral part of natural temperate forests. The North American populations that were decimated by the fur trade are beginning to recover, but the long absence of beavers from forest streams has had a severe impact on other species. |
| Both temperate and tropical forests are home to a wide variety of rodents. Most are arboreal but other species are burrowers or even aquatic. Rodents are some of the most important seed dispersers, often collecting more seeds than they can eat and burying them for later use. This type of behaviour is common among squirrels throughout North American forests. Inevitably, some of the seed stores are forgotten, or the squirrel is killed before it can return to use them. The seeds end up sprouting where the animal "planted" them, often a location they would not have been able to reach otherwise. |
 A chipmunk feeding on seeds, well camouflaged. Photo by Maya Walters. |
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Rodents are the most
diverse group of mammals. Almost 45% of all mammal species in the world are rodents.
Left: This chipmunk has lost its tail, perhaps due to a fight or a predator. Photo by Maya Walters. |
| Rodent populations are very diverse even in the temperate regions. In the Sierra Nevada mountains, there are eight distinct species of chipmunks alone. They are all very similar in appearance, but each species inhabits its own particular habitat. Although most would be able to survive in several of the other species' habitats, they aggressively keep each other out. |
related topics
[tropical rainforests] [arboreal adaptations] [forests through time] [biodiversity] [leaves] [seeds & fruit]
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