Niche and Community Interactions and Population Growth

Niche A niche is the range of physical and biological conditions in which a species lives and the way the species obtains what it needs to survive and reproduce.

Tolerance Every species has its own range of tolerance, the ability to survive and reproduce under a range of environmental circumstances.

Tolerance Organisms have an upper and lower limit of tolerance for every environmental factor. Beyond those limits, the organism cannot survive.

Tolerance When an environmental condition, such as temperature, extends in either direction beyond an organism’s optimum range, the organism experiences stress. The organism must expend more energy to maintain homeostasis, and so has less energy left for growth and reproduction.

Habitat A species’ tolerance for environmental conditions, then, helps determine its habitat—the general place where an organism lives.

Niche and Resources The term resource can refer to any necessity of life, such as water, nutrients, light, food, or space. For plants, resources can include sunlight, water, and soil nutrients. For animals, resources can include nesting space, shelter, types of food, and places to feed.

Polar bears live in the arctic. The arctic is their a. niche. b. habitat. c. tolerance. d. microclimate.

Which of the following is a biological aspect of an organism’s niche? a. the water in the area b. the way it gets food c. amount of sunlight d. composition of soil

Competition How one organism interacts with other organisms is an important part of defining its niche. Competition occurs when organisms attempt to use the same limited ecological resource in the same place at the same time.

Intraspecific Competition Competition between members of the same species.

Interspecific Competition Competition between members of different species.

Competitive Exclusion Principle Direct competition between different species almost always produces a winner and a loser—and the losing species dies out. Dotted line – grown separately Solid line – grown together

Competitive Exclusion Principle The competitive exclusion principle states that no two species can occupy exactly the same niche in exactly the same habitat at exactly the same time.

Dividing Resources Instead of competing for similar resources, species usually divide them.

Dividing Resources The resources utilized by these species are similar yet different. Therefore, each species has its own niche and competition is minimized.

No two species can occupy the same niche in the same habitat at the same time a. because of the interactions that shape the ecosystem. b. unless the species require different abiotic factors. c. because of the competitive exclusion principle. d. unless the species require different biotic factors.

Several species of warblers can live in the same spruce tree ONLY because they a. have different habitats within the tree. b. don’t eat food from the tree. c. occupy different niches within the tree. d. can find different temperatures within the tree.

Predator-Prey Relationships An interaction in which one animal (the predator) captures and feeds on another animal (the prey) is called predation.

Predator Prey Relationships Predators can affect the size of prey populations in a community and determine the places prey can live and feed. Idealized computer model

Herbivore Plant Relationship An interaction in which one animal (the herbivore) feeds on producers (such as plants) is called herbivory.

Herbivore Plant Relationship Herbivores, like a ring- tailed lemur, can affect both the size and distribution of plant populations in a community and determine the places that certain plants can survive and grow.

Keystone Species A keystone species is one whose impact on its community or ecosystem is disproportionately large relative to its abundance .

Keystone Species A species whose very presence contributes to the diversity of life and whose extinction would result in the extinction of species dependant on it.

Symbiosis The close and often long- term interactions between biological species. Mutualism Parasitism Commensalism

Mutualism Also known as cooperation. Both organisms gain a fitness benefit. Ex, clown fish and anemone

Parasitism Relationships in which one organism lives inside or on another organism and harms it. Generally, parasites weaken but do not kill their host, which is usually larger than the parasite.

Commensalism A relationship in which one organism benefits and the other is neither helped nor harmed. Ex, barnacles on whale

Population Growth

Growth Rate A population’s growth rate determines whether the population size increases, decreases, or stays the same.

Population Growth A population will increase or decrease in size depending on how many individuals are added to it or removed from it.

Birthrate and Deathrate A population can grow when its birthrate is higher than its death rate. If the birthrate equals the death rate, the population may stay the same size. If the death rate is greater than the birthrate, the population is likely to shrink.

Which of the following is NOT one of the factors that play a role in population growth rate? a. immigration b. death rate c. emigration d. demography

The movement of organisms into a range is called a. immigration. b. emigration. c. population shift. d. carrying capacity.

Which of the following could describe a population that is decreasing in size? A) The birthrate and the death rate remain the same. B) The death rate is becoming lower than the birthrate. C) The death rate is constant and the birthrate is increasing D) The death rate is becoming higher than the birthrate.

Exponential Growth Under ideal conditions with unlimited resources, a population will grow exponentially. In exponential growth, the larger a population gets, the faster it grows.

Exponential Growth If you plot the size of this population on a graph over time, you get a J-shaped curve that rises slowly at first, and then rises faster and faster.

Logistic Growth Logistic growth occurs when a population’s growth slows and then stops (most populations experience this type of growth) follows a period of exponential growth.

3 Phases of Population Growth

Carrying Capacity Carrying capacity is the maximum number of individuals of a particular species that a particular environment can support.

Which of the following could describe a population that is decreasing in size? A) The birthrate and the death rate remain the same. B) The death rate is becoming lower than the birthrate. C) The death rate is constant and the birthrate is increasing. D) The death rate is becoming higher than the birthrate.

The graph in Figure 5–1 shows the growth of a bacterial population The graph in Figure 5–1 shows the growth of a bacterial population. Which of the following correctly describes the growth curve? A) logistic B) limiting C) demographic D) exponential

Suppose that a species of toads is introduced into a new environment in an attempt to reduce the population of insects. The toad has no natural predators in the new environment. The toad population would most likely A) increase exponentially. B) increase logistically. C) decrease rapidly and die out. D) remain the same.

If a population grows larger than the carrying capacity of the environment, which of these is most likely to happen? A) The death rate may rise. B) The birthrate may rise. C) The death rate must fall. D) The birthrate must fall.

Limiting Factors A limiting factor is a factor that controls the growth of a population. Some depend on population density and others do not.

Density Dependent Factors Density-dependent limiting factors include competition, predation, herbivory, parasitism, disease, and stress from overcrowding.

Competition When populations become crowded, individuals compete for food, water, space, sunlight, and other essentials.

Competition Competition is a density-dependent limiting factor. The more individuals living in an area, the sooner they use up the available resources.

Predation and Herbivory The effects of predators on prey and the effects of herbivores on plants are two very important density- dependent population controls.

Herbivore Effects Herbivory can also contribute to changes in population numbers. From a plant’s perspective, herbivores are predators.

Humans as Predators In some situations, human activity limits populations. Fishing fleets have raised cod death rates so high that birthrates cannot keep up. As a result, cod populations have been dropping.

Parasitism and Disease Parasitism and disease are density-dependent effects, because the denser the host population, the more easily parasites can spread from one host to another.

Parasitism and Disease This graph shows a sudden and dramatic drop in the wolf population of Isle Royale around 1980. At this time, a viral disease of wolves, canine parvovirus (CPV), was accidentally introduced to the island.

Stress from Overcrowding Overcrowding causes stress in populations Lowers ability to fight disease Causes some females to neglect or even eat their young

Density Independent Factors Density-independent limiting factors affect all populations in similar ways, regardless of population size and density. Unusual weather such as hurricanes, droughts, or floods, and natural disasters such as wildfires, can act as density-independent limiting factors.

Each of the following is a density-dependent limiting factor EXCEPT A) competition. B) temperature. C) crowding. D) disease.

Which would be least likely to be affected by a density-dependent limiting factor? A) a small, scattered population B) a population with a high birthrate C) a large, dense population D) a population with a high immigration rate

Which of the following is a density-independent limiting factor? A) earthquake B) disease C) emigration D) parasitism