Why do you think populations do not grow infinitely?

Transcription

1 Do Now 3/15/16 Why do you think populations do not grow infinitely? Teaching Point SWBAT: 1) Differentiate logistic and exponential growth 2) Identify what factors affect population growth and the carrying capacity

2 Populations A population is a group of organisms of a single species that lives in a given area. The area inhabited by a population is called its geographic range. A population s range can vary enormously in size, depending on the species. Population density refers to the number of individuals per unit area. Individuals in a population are either spaced out randomly, uniformly, or clumped.

3 Populations A population s growth rate determines whether the size of the population increases, decreases, or stays the same. Populations also have an age structure, or the number of males and females of each age a population contains.

4 Population Growth A population may grow if individuals move into its range from elsewhere, which is called immigration. The opposite of immigration is emigration, where a population decreases in size when individuals move out of the population s range.

5 Population Growth When there is unlimited resources, a population will grow exponentially. This exponential growth means that the larger a population gets, the faster it grows. This growth is shaped like a J on a graph.

6 Population Growth When there is not unlimited resources, logistic growth happens. Logistic growth is shaped liked a S on a graph. Logistic growth happens when: 1. A population grows rapidly 2. Growth slows 3. The growth stops

7 Population Growth The growth will stop at a certain population size. This population size is called the carrying capacity. The carrying capacity is the maximum number of individuals of a particular species that a particular environment can support.

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9 So Why Does Logistic Growth Happen Populations show logistic growth ( S shape) because of limiting factors exist in the environment. Limiting factors are factors that control the growth of a population. There are several kinds of limiting factors that are depending on how big the population is; such as competition, predation, parasitism, and disease.

10 So Why Does Logistic Growth Happen Others, like natural disasters and unusual weather, do not depend on how big the population is. Acting separately or together, limiting factors determine the carrying capacity of a population.

11 Density-Dependent Limiting Factors Density-dependent limiting factors happen when the population density, or the number of organisms in a certain space, reaches a certain level. These factors do not affect small populations. Examples of density-dependent limiting factors are competition, predation, herbivory, parasitism, and disease.

12 Density-Dependent Limiting Factors Competition depends on the size of a population because the more individuals living in an area, the sooner they use up the available resources. The size of the predator and prey populations can affect the size of each other. The populations of predators and prey can cycle up and down at times. Herbivores and plants follow the same pattern.

13 Density-Dependent Limiting Factors Parasitism and disease depends on population size because the larger the host population, the more easily parasites and disease can spread from one host to another.

14 Density-Dependent Limiting 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, as well natural disasters like wildfires can act as densityindependent limiting factors.

15 Let s review the Population Distribution Worksheet: Questions:

16 What Now 1) Work on the Guided Practice individually or with a partner 2) When finished, let a teacher check your work and stamp the paper 3) If not finished by the end of class, it is homework 4) If you finish before class, complete any missing work

17 Closure Underneath your teaching points: What is the difference between densitydependent and density-independent limiting factors?