Biodiversity, Species Interactions, and Population Control
Two major factors affect the number of species in a community: the latitude in terrestrial communities and salinity/nutrients in aquatic systems.
Species play different roles in a community. Native species sustain the ecosystem in which they are a part. Some nonnative species will crowd out native species. Indicator species alert us to harmful changes in the community. Keystone species play ecological roles in the specific community: they may assist in pollination help regulate populations. Foundation species affect the community’s habitat to benefit other species.
Species interact with each other in these different ways: interspecific competition, predation, parasitism, mutualism, and commensalism.
As environmental conditions change, one species may be replaced by other groups of species. This gradual change in the composition of species in a given area is called ecological succession.
A community has three aspects of sustaining itself: its persistence, the ability to resist being altered, its constant population, and its resilience in repairing damage. High biodiversity may give a community some edge in surviving, but we do not know this for certain.
Key Questions and Concepts
5-1 How do species interact?
CORE CASE STUDY. Sea otters are a keystone species found on the west coast of the United States that are endangered. For many years they have been in recovery. Why should we be concerned about their status? Sea otters are charismatic, they generate tourist revenue, and they are very valuable in terms of controlling biological populations.
A. Five basic species interactions are competition, predation, parasitism, mutualism, and commensalism. B.
Competition between species for food, sunlight, water, soil, space, nest sites, etc. is interspecific competition. 1.
With intense competition for limited resources, one species must migrate, shift its feeding habits/behavior, or face extinction. 2.
As humans take more and more space, other species are compromised. C.
In competitive situations, some species evolve adaptations that reduce/avoid competition for resources. 1.
Over a long time, species evolve more specialized traits that allow them to use shared resources at different times, in different ways, or in different places; this is termed resource partitioning. 2.
Predator-prey relationships define one species (the predator) feeding/preying on another. 3.
Predators have a variety of ways to capture prey. Herbivores feed on immobile plant species; carnivores use pursuit of prey or ambush to capture prey. Some predators use camouflage, and others use chemical warfare (venom) to capture prey or deter predators. 4.
Prey species escape predators in a number of different ways such as swift movement, protective shells, camouflage, or use of chemicals to repel or poison.
SCIENCE FOCUS: Giant kelp forests are very productive and biologically diverse ecosystems. Sea urchins are a major threat to kelp, but sea otters keep their populations in check. Polluted water and the warming of the world’s oceans also threaten kelp forests. If kelp forests decline significantly, many other species could be affected. 5. Coevolution is when predator and prey can exert intense natural selection pressures on one another.
D. Parasitism, mutualism, and commensalism.
1. Parasites live on or in another species. The host of this arrangement is obviously harmed by it, but the parasite can contribute to biodiversity by controlling the size of specific species populations. 2. Mutualism is a relationship that benefits both species; these benefits can be in dispersing pollen and seeds for reproduction, in receiving food, or in receiving protection. a. Mutualism is not cooperation; each species exploits the other. E.
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