Biodiversity, Species Interactions, and Population Control Chapter 5

5-1 How Do Species Interact? Concept 5-1 Five types of species interactions – competition, predation, parasitism, mutualism, and commensalism – affect the resource use and population sizes of the species in an ecosystem.

Species Interactions

COMPETITION Organisms compete for shared or limited resources such as food, water, space, and habitats. Competitive exclusion principle – No two species can occupy the exact same niche for very long More in Section 5-2

COMPETITION Interspecific competition is the competition between member of two different species. The result is that neither species can obtain as many resources as they could in the absence of the other species. Intraspecific competition is the competition between member of the same species. This also includes the competition for mates.

PREDATION Species called predators feed on other species called prey. Organisms use their senses to locate objects and their prey. Some predators are fast enough to catch their prey, some hide and lie in wait, and some inject chemicals to paralyze their prey.

PREDATION Some prey may escape their predators by: Camouflage Outer protection Chemical warfare Warning coloration Mimicry Deceptive looks Deceptive behavior

Predator and Prey Species Can Drive Each Other’s Evolution Intense natural selection pressures exist between predator and prey populations Coevolution – changes in the gene pool of one species can lead to changes in another species Evolution in the predator population – improved abilities to capture prey Evolutionary response – the prey improves its abilities to avoid capture The evolution of improved escape abilities should result in increased capture abilities. Evolutionary “arms race” The levels of defense and counter-defense will continue to escalate.

Parasitism Parasitism occurs when one species feeds on part of another organism. Although parasites can harm their hosts, they can promote community biodiversity. Some parasites live inside the host (micororganisms, tapeworms). Some parasites live outside the host (fleas, ticks, mistletoe plants, sea lampreys). Some have little contact with host (cowbirds – lay eggs in another’s nest…let them take care of young.)

Parasitism

Mutualism In mutualism, two species interact in a way that benefits both of them. Most organisms benefit through mutualistic interactions by gaining nutrition or protection.

Commensalism Commensalism is an interaction that benefits one species but has little, if any, effect on the other species. Epiphytes

5-2 How Can Natural Selection Reduce Competition between Species? Concept 5-2 Some species develop adaptations that allow them to reduce or avoid competition with other species for resources.

5-2 How Can Natural Selection Reduce Competition between Species? Niches (way of life) become separated to avoid competition for resources. Reduce niche overlap This is also the basis of natural selection – the pressure that drives the evolution of new species. Chapter 4

5-2 How Can Natural Selection Reduce Competition between Species? Some species evolve adaptations that allow them to reduce or avoid competition for resources with other species (resource partitioning). Each species minimizes competition with the others for food by spending at least half its feeding time in a distinct portion of the spruce tree and by consuming somewhat different insect species.

5-2 How Can Natural Selection Reduce Competition between Species? Genetic variation and specialized feeding niches can lead to evolutionary divergence. Use shared resources at different: Times Places Ways Each species has a beak specialized to take advantage of certain types of food resource.

5-4 How Do Communities and Ecosystems Respond to Changing Environmental Conditions? Concept 5-4 The structure and species composition of communities and ecosystems change in response to changing environmental conditions through a process called ecological succession.

5-4 How Do Communities and Ecosystems Respond to Changing Environmental Conditions? New environmental conditions allow one group of species in a community to replace other groups. Ecological succession: the gradual change in species composition of a given area Primary succession: the gradual establishment of biotic communities in lifeless areas where there is no soil or sediment. Secondary succession: series of communities develop in places containing soil or sediment.

5-4 How Do Communities and Ecosystems Respond to Changing Environmental Conditions? Primary succession begins with an essentially lifeless area where there is no soil. The weathering of rocks and the introduction of hearty plants begins to form soil. Eventually, more and more plant species are able to take hold. This process takes a very long time. (100’s -1000’s of years)

5-4 How Do Communities and Ecosystems Respond to Changing Environmental Conditions? Primary succession begins with an essentially lifeless area where there is no soil.

Early successional plant species, pioneer 5-4 How Do Communities and Ecosystems Respond to Changing Environmental Conditions? Early successional plant species, pioneer Lichens, mosses Trap windblown sediments, moisture Break apart rocks Midsuccessional plant species Grasses, low shrubs Late successional plant species Mostly trees

5-4 How Do Communities and Ecosystems Respond to Changing Environmental Conditions? Secondary succession occurs when the natural community has been disturbed, removed, or destroyed. This disturbance could be as a result of a fire, flood, or humans. The key is that soil already exists so that this process many only take a 100-200 years.

5-4 How Do Communities and Ecosystems Respond to Changing Environmental Conditions? Secondary succession occurs when the natural community has been disturbed, removed, or destroyed.

Succession Doesn’t Follow a Predictable Path The course of succession cannot be precisely predicted. Traditional view Balance of nature and a stable climax community will always be achieved. Current view Ever-changing mosaic of patches of vegetation Succession involves species competing for enough light, nutrients and space which will influence it’s trajectory and end result. State of continual disturbance and change