Interactions in the Ecosystem Chapter 5 (pg 72-87) Mrs. Paul

5.1 HABITATS AND NICHES Habitat: the place where an organism lives. Each organism is adapted to its habitat. Have special ways of gathering food, reproducing, avoiding predators. Ecosystems contain many different habitats and organisms.

Niches Niche: the role of an organism in the ecosystem. What an organism does within its habitat. Includes biotic and abiotic factors (food sources, predators/temperature, amount of sunlight and water). All members of a species adapted to same niche---2 species may NOT share the same niche.

Example: Anolis lizard All of this type of lizard vary ONLY by the size of insects that they eat. Large jaws eat large insects. Small jaws eat small insects. Occupy DIFFERENT niches.

What if 2 species try to share the same niche? Compete for resources (some will get more of what they need to survive and some will get less). Competitive Exclusion:the extinction of a population due to direct competition with another species for a resource.

Species A Chthamalus stellatus Species B Balanus balanoides Example: The actions of species A influences the niche of species B! Species A Chthamalus stellatus Species B Balanus balanoides

There is a difference between the role a an organism CAN fill in the environment vs. the role it actually fills when it interacts with other species in the environment. Fundamental niche: the theoretical role an organism plays in its habitat. Realized niche: the actual role the organism plays in its environment.

Fundamental niche vs. Realized niche…

Niche Diversity Determined by the abiotic factors in the environment. If the physical conditions of a place are fairly constant, then there will be less diversity. Differences in temperature and moisture. Predator: an organism that actively hunts other organsims. Can increase niche diversity. Decrease population size of their prey species, then more resources become available for another species.

Example: remove sea stars from tide pools and mussels increased until they “outcompeted” other species. Number of species in tide pool decreased from 15 to 8.

Keystone predator: a predator that causes a large increase in the diversity of its habitat.

Check for Understanding: How is a niche different from a habitat? What is competitive exclusion? How is it related to the concept of the niche? What might happen to an ecosystem if all the carnivores were removed? Explain your answer.

5.2 EVOLUTION AND ADAPTATION A change in the environment affects all the organisms in the environments and their niches. If a niche disappears, a species may become extinct. Evolution: change in a population of organisms over time. One way populations respond to a changing environment.

Evolving to the Niche May change for several reasons: To adapt to niches in environment. Avoid competition with another species. Example: 5 species of Warblers eating insects in spruce trees…

Each of the 5 species has evolved into a narrow niche (they eat insects in different parts of the spruce trees) Specialized niche: an organism with a small or very specific role in the habitat. Example: giant panda only eats bamboo leaves Vulnerable to extinction-can’t deal with change in environment. Generalized niche: an organism with a wide or more general role in the habitat. Example: mice or cockroaches.

CONVERGENT EVOLUTION Organisms living in similar ecosystems with similar niches may become alike as they adapt to the similar conditions. Convergent evolution: the development of similar adaptations in two species with similar niches. Example: wings of birds and bats, dolphin and ichthyosaur.

Coevolution Organisms that interact closely may have evolutionary responses to each other. Coevolution: species that interact closely may adapt to one another. May be between predator and prey (plants and caterpillar), species that cooperate (acacia trees and the stinging ants that live on them).

Check for Understanding: Why do species such as the warblers in Figure 5.5 evolve avoid competition with other species? Explain convergent evolution and give one example. Why does convergent evolution happen? What would happen to the ant colony living on an acacia tree if that tree was chopped down? What does your answer imply about the effect of destroying an organism’s habitat?

5.3 POPULATIONS

Population: a group of organisms of the same species that live together in an area and interbreed. As the environment changes, the size of the population changes.

Population Growth Thomas Malthus Observed that human population can quickly grow beyond what the environment can support. Result in famine and disease

Populations have the ability to grow very quickly. Exponential growth: population growth in which the rate of growth in each generation is a multiple of the previous generation. In reality, a population cannot continue to grow like this due to limited resources.

Carrying Capacity As a population increases, available resources decrease (water, food, space, etc). Competition increases as there is no longer enough for everyone. Those who don’t get resources die (death rate increases, birth rate decrease…having babies requires a lot of resources). Population growth slows down.

Population growth = population death The population is no longer getting bigger. Carrying capacity: number of individuals that can be supported by an ecosystem. Resources that are available will determine the carrying capacity. Carrying capacity is the maximum population size.

Limiting Factors Limiting factors: forces that slow the growth in a population. Examples: natural disasters, human disturbance, water availability, living space, food competition, disease, parasitism, predation, climate. Two types of limiting factors: 1. Density-dependent limiting factors 2. Density-independent limiting factors.

Density-Dependent Limiting Factors Limiting factors that are dependent on population size. Affect a population more strongly as the population gets bigger. Examples: lack of food, predation, disease

Density-independent Limiting Factors Limiting factors that affect the same percentage of the population, no matter how big the population becomes. Affect a population the same amount each time. Examples: natural disasters, human habitat damage.

Human Populations Growth of human population is exponential. Caused by many factors: advances in agriculture, technology, and medicine.

Check for Understanding: What is exponential growth? Under what conditions do populations grow exponentially? What is the difference between density- dependent and density-independent limiting factors?