Populations
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When we look at a lake, pond, stream or the ocean, we rarely see much of the diversity that abounds inside of it. A terrestrial landscape is different. For example, look at the tropical rain forest below. You see plants everywhere. If you look closely, you will notice that many of them look different, since they are separate species. However, seeing nonplant species such as animals becomes challenging. It takes ecologists patience, hard work and skill to determine the vast assemblage of all the species that may inhabit this forest.
might contain three jaguars per 200 hectares (500 acres). This population abundance level is referred to as the density of the species. The size of each population can increase by births and movement of some members of the species into the area (immigration). Vice versa, deaths and movement out of the area (emigration) would reduce the size of the population. Ultimately, most populations do not keep growing in abundance, or else they would use up all the resources in the area. Such factors as predation, disease and severe weather conditions reduce survival no matter how good their adaptations are for avoiding death. This upper limit of population growth is referred to as the carrying capacity of the area we have defined. In other words, a specific number of hectares has the resources to support a certain number of members of each species.
Ecologists often rely on various types of survey strategies to help them determine what is present. Careful observations will yield a kaleidoscope of life beyond the vast number of trees, vines, and flowers that abound there. The diagram to the right illustrates some of the species of animals that might be observed or captured in traps. However, what the diagram fails to convey is that each species has a specific level of abundance.
This number of members of a species in a certain location at a distinct point in time is called a population. Thus, for every species in the forest, there would be a population in the area that we defined
(e.g., a hectare). For example, the forest
This number of members of a species in a certain location at a distinct point in time is called a population. Thus, for every species in the forest, there would be a population in the area that we defined
(e.g., a hectare). For example, the forest
In the forest, jaguars, Panthera onca, like all organisms in the Biosphere, are living in populations. Textbook diagrams often fail to convey this principle since illustrations of forest animals usually only show one representative.
Credits: Tropical Rain Forest (Andre Nantel|Dreamstime) / Tropical Rain Forest Animals, Jaguars (Dorling Kindersley)