CHAPTER 5 How Populations Grow

Food Chain -sea otters, giant kelp, smaller kelp, sea urchins At one time sea otters were almost eliminated by hunting; sea urchin populations increased and kelp forests nearly disappeared. Why?

The kelp was eaten by hordes of sea urchins! Sea otters were declared an endangered species and were protected from hunting.

Sea otters were declared an endangered species and were protected from hunting. The sea otters population _________. Sea urchin populations____________. Kelp populations______________.

CHARACTERISTICS OF POPULAITONS 4 important characteristics of a population are i. ii. iii. iv.

CHARACTERISTICS OF POPULAITONS 3 important characteristics of a population are i. Geographic distribution ii. Density iii. Growth Rate iv. Density independent/dependent factors

1. Georgraphic distribution is a term that describes the area inhabited by a population. The range can vary in size from a few cubic centrimeters occupied by bacteria in a rotting apple to the millions of square kilometers occupied by migrating whales in the Pacific Ocean.

Population Density is the number of individuals per unit area. -this number can vary depending on the species and its ecosystem. Growth Rate: 3 factors can affect population size: I. # of births ii. # of deaths iii. # of individuals that leave or enter the population

Immigration is the movement of individuals into an area. Emigration is the movement of individuals out of a population.

Under ideal conditions and unlimited resources, a population will continue to grow in a pattern called exponential growth. As resources are used up and population growth slows or stops, the population exhibits logistic growth.

GROWTH OF A POPULATION WILL EVENTUALLY SLOW DOWN. WHY? Resources become less available. Ex. Food, space, water Birth rate decreases. Death rate increases. Increased emigration 5. Decreased immigration

The carrying capacity of an environment for a particular species is the largest number of individuals that the environment can support. Refer to the logistic growth curve.

FACTORS THAT LIMIT THE GROWTH OF A POPULATION A limiting factor is a factor that causes population to decrease. Density-Dependent Factors Density- Independent Factors

Density-Dependent Factors Competition Predation Parasitism iv. Disease

Density-Dependent Factors Competition -when populations become crowded, organisms compete for food, water, space, sunlight, and other essentials. Ex. Birds compete for limited nesting sites.

Density-Dependent Factors Competition -when populations become crowded, organisms compete for food, water, space, sunlight, and other essentials. Ex. Birds compete for limited nesting sites. -the more individuals living in an area, the sooner they use up the available resources.

Density-Dependent Factors Competition -when populations become crowded, organisms compete for food, water, space, sunlight, and other essentials. Ex. Birds compete for limited nesting sites. -the more individuals living in an area, the sooner they use up the available resources. competition can occur btw members of the same species or btw members of different species.

Density-Dependent Factors Competition -when populations become crowded, organisms compete for food, water, space, sunlight, and other essentials. Ex. Birds compete for limited nesting sites. -the more individuals living in an area, the sooner they use up the available resources. competition can occur btw members of the same species or btw members of different species. -when 2 species compete for the same resources both species are under pressure to change in ways that decrease their competition - the species over time may evolve to occupy separare niches.

Density-Dependent Factors Predation Populations in nature are often controlled by predation, within a predator-prey relationship. Ex. The relationship btw a sea otters and sea urchins and btw sea otters and killer whales are examples of predator-prey relationships that affect population growth. Ex. Wolves and Moose - refer to fig 5-7 p126.

Density-Dependent Factors iii. Parasitism and iv. Disease Like predators, parasites take nourishment at the expense of their hosts, often weakening them and causing disease or death. Ex. Wasp cacoons can weaken or kill many caterpillars. Fig 5-8 p126. -the wasp inserts its eggs beneath the moth’s skin. After hatching, the wasp larvae feed on their host internally until they appear as white cacoons on its back.

Density- Independent Factors Affects all populations in a similar way, regardless of the population size. For example i. Weather Natural Disasters Seasonal Cycles Certain human activities such as clear cutting forests.

Practice Questions P 135 Ch 5 Assessment Q 1-8; 11-19, 23 P137 Prep Test - do all questions.