Fundamentals of Biogeography and EcosystemsBiogeography and ecological systemsBiogeography is the study of the geographical patterns of plant and animal species. To understand the distribution of plant and animal species on Earth, a fundamental knowledge of ecology and ecosystem dynamics is required. Ecology is the study of the interactions among organisms. An ecosystem is a functioning entity of all the organisms in a biological system generally in equilibrium with the inputs and outputs of energy and materials in a particular environment. It is the basic ecological unit of study. There are two kinds of ecosystems, aquatic and terrestrial. An ecosystem is comprised of habitats, biological communities, and ecotones. A biome is often referred to as a global-scale community of plants and animals and is the largest subdivision of the biosphere. A biome may contain many different kinds of smaller ecosystems. Biomes are typically distinguished on the basis of the characteristics of their vegetation because it makes up the largest portion of biomass. Biomes are subdivided by formation class, vegetation units of a dominant species. Plants and animals disburse across the Earth and occupy habitats favorable for their survival. A habitat is the specific, physical location of an organism-- it's where they live. Most African elephants live on savannas and in dry woodlands. Bass prefer a habitat of warm, calm, clear water and is usually found in slow-moving streams, ponds, lakes, and reservoirs. Habitats can be identified at different spatial scales. Macrohabitats are delineated by climate and subdivided on the basis of their vegetation. Microhabitats are smaller in size, such as the habitat along a stream channel or a layer within the canopy of a rain forest. Each species has specific habitat parameters (temperature, moisture and nutrient availability). Within a habitat, organisms "occupy" a niche. A niche is the function or occupation, of a life-form within a community. An organism's niche incorporates the physical (habitat), chemical, and biological factors that maintains the health and vitality of the organism. An organism's interaction with the abiotic factors of its environment (heat and moisture) defines its niche. The food requirements, and those that prey on it, are part of the organism's niche. A niche, therefore, is the sum of an organism's physiological adaptation to and interaction with its physical environment. Biogeographical RealmsHabitat occupation may be "limited" due to the ability for plants and animals to disperse throughout the environment. Even though a habitat is available for occupation, barriers to diffusion may prevent organisms from inhabiting them. Habitat occupation may depend on several factors. First is the location of centers of evolution called biogeographical realms.
Figure BE. 1 Biogeographical Realms Biogeographical realms are geographical regions out of which particular assemblages of plants and animals evolved and dispersed. The Nearctic realm possesses a great diversity of biomes including the tundra, grassland, deciduous and coniferous forest, chaparral, and desert biomes. The Nearctic realm has been separated from Neotropical by deserts, and until recently, an absence of a land bridge between them. The Palaearctic realm is very similar to the Nearctic in terms of the diversity of biomes including tundra, grassland, deciduous and coniferous forest, chaparral, and desert biomes. The Neotropical realm is dominated by tropical forests, savannas, and deserts. The Afrotropical realm is inhabited by tropical forests, savannas, and deserts. It is separated from Palaearctic realm by the Sahara desert; previously separated by an arm of the sea. The Australian (or Australasian) realm has a desert core, surrounded by tropical forest and savanna. The Australian realm boasts a unique variety of plants and animals as they have evolved in isolation from outside influence. Pouched marsupial mammals, like the Kangaroo, are found in the Australian realm. The Indomalayan realm is nearly exclusively tropical forest. It was isolated from the Palaearctic by the Himalayan Mountains. The Indomalayan realm was previously separated by a sea lane that has subsequently been closed by continental drift. The Antarctic realm exhibits a diverse set of ecosystems from temperate forest and grassland in New Zealand to tundra and ice sheets in Antarctica. Many of New Zealand's mammals are like those frequenting Antarctic shores. Finally the Oceanian realm is dominated by tropical forests. Physical barrier are often the most imposing barriers to diffusion. Impassable topography, large water bodies, and unsuitable climates are all impediments for the dispersal of plant and species. |
