Two different types of succession, primary and secondary, have been distinguished. Primary succession occurs in essentially lifeless areas—regions in which the soil is incapable of sustaining life as a result of such factors as lava flows, newly formed sand dunes, or rocks left from a retreating glacier. Secondary succession occurs in areas where a community that previously existed has been removed; it is typified by smaller-scale disturbances that do not eliminate all life and nutrients from the environment. Events such as a fire that sweeps across a grassland or a storm that uproots trees within a forest create patches of habitat that are colonized by early successional species. Depending on the extent of the disturbance, some species may survive, other species may be recolonized from nearby habitats, and others may actually be released from a dormant condition by the disturbance. For example, many plant species in fire-prone environments have seeds that remain dormant within the soil until the heat of a fire stimulates them to germinate.
Transfer-of-energy-through-an-ecosystemFigure 2: Transfer of energy through an ecosystem. At each trophic level only a small proportion of …[Credits : Encyclopædia Britannica, Inc.]
Generalized-aquatic-food-webFigure 1: Generalized aquatic food web. Parasites, among the most diverse species in the food web, …[Credits : Encyclopædia Britannica, Inc.]
Male-resplendent-quetzal-or-resplendent-trogonMale resplendent quetzal, or resplendent trogon (Pharomachrus mocinno).[Credits : Michael & Patricia Fogden]
Parasitoids-which-parasitize-other-arthropods-by-depositing-eggs-in-theFigure 2: Parasitoids, which parasitize other arthropods by depositing eggs in the pupae, larvae, …[Credits : Encyclopædia Britannica, Inc.]
DOrbignys-round-eared-bat-capturing-a-katydid-in-flightD’Orbigny’s round-eared bat (Tonatia silvicola) capturing a katydid in flight.[Credits : © Merlin D. Tuttle, Bat Conservation International—Photo Researchers, Inc.]
Silky-anteater-extending-its-long-narrow-tongue-which-it-usesSilky anteater (Cyclopes didactylus) extending its long, narrow tongue, which it uses to …[Credits : Gunter Ziesler/Bruce Coleman Ltd.]
Coevolution-between-the-yucca-moth-and-the-yucca-plantCoevolution between the yucca moth and the yucca plant. (Top) A female yucca moth …[Credits : Photographs, © Robert and Linda Mitchell]Coevolution between the yucca moth and the yucca plant. (Top) A female yucca moth …[Credits : Photographs, © Robert and Linda Mitchell]
Coevolution-of-one-species-with-many-speciesCoevolution of one species with many species. (Top) European cuckoo (Cuculus canorus) …[Credits : John Markham/Bruce Coleman Ltd.]Coevolution of one species with many species. (Top) European cuckoo (Cuculus canorus) …[Credits : John Markham/Bruce Coleman Ltd.]
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