Limiting Factors & Carrying Capacity

Lets think about it… Appendix 1.1. – Environmental factors and population size Activity #1: Animal Crackers

Definitions: Population: the total number of animals/plants/things of one type in a particular area Example: All the geese in Birds Hill Provincial Park. All of the water beetles in a pond. All the desks in this room.

What is a Limiting Factor? Limiting Factors are… (two similar definitions) conditions of the environment that limit the growth of a species. biotic and abiotic factors that prevent the continuous growth of a population.

What is a Limiting Factor? Populations would continue to increase if they had all of the resources they require in unlimited amounts, but there are always factors that limit their increase. Limiting factors control population growth.

Let’s list some Limiting Factors!

Can a population continue to grow at this rate forever? The answer, of course, is no. The environment becomes limiting. Resources such as food and water become scarcer and the rate of population increase begins to slow. The graph below illustrates a population growth curve of this nature.

Think back to the housefly problem Think back to the housefly problem. Over the months the number of flies increased from 900 flies in January. 400 000 flies by late February. 180 000 000 flies in March. The number of flies increased slowly at first and then very rapidly. However; having a few hundred million flies in your home in March is highly unlikely. Why is this so?

What is Carrying Capacity? Because of these limiting factors, each ecosystem has a finite capacity for growth connected to its carrying capacity.

What is Carrying Capacity? Carrying capacity is the number of individuals of a species that an ecosystem can support.

Steady state phase – population has reached its carrying capacity Exponential growth phase – population grows rapidly Decline phase – population decreases due to: Lag phase – population is slowly increasing

There are four main factors that affect the carrying capacity of an ecosystem. Materials and Energy: All populations are affected by the amount of usable energy from the Sun (which could be in the form of animals or plants) as well as water and carbon supply. Food Chains: Populations at one trophic level are affected by the number in all levels above and below it. i.e: Populations are affected by their food supply. (The animals/plants below it in a food web. Populations are also limited by their predators. (The animals above them on a food web.)

Competition: The demand for resources such as food, water, mates, and space. This also affects the carrying capacity of an ecosystem. Density: Depending on an animal’s need for space this determines their population density. (Population density is how many animals can live in an area at a time.)

Competition: The demand for resources such as food, water, mates, and space. This also affects the carrying capacity of an ecosystem. There are two types of competition: intraspecific competition: competition among the same species Example: The competition between two bears in the same territory.

interspecific competition: competition among different species Example: The competition between a bear and a wolf in the same territory.

Water Disease Food Shelter/ Space There are two types of factors that affect population density: density-dependent factors: These are factors that increase in importance as population grows. These things are influenced by an increase or a decrease in population. Examples: food supply, disease Water Disease Shelter/ Space Food

Natural Disasters Hunting Logging density-independent factors: These are factors that affect populations regardless of their size to begin with. These factors will take place regardless of an increase or decrease in population. Examples: forest fires, predators, natural disasters, floods, droughts *Factors that limit the size of a population but DO NOT depend upon the size of the population.* Hunting Natural Disasters Logging

On Graphs If you draw a line through the middle of the population fluctuations, that line represents the carrying capacity of that environment for that species. Go back to Population Growth Curve 2 and draw a line that represents the carrying capacity.

Population Growth Curve: Carrying Capacity

Limiting Factors In nature, populations of organisms rarely grow uncontrolled. Each ecosystem has a carrying capacity (or number or organisms it can sustain/support). Remember, limiting factors are biotic and abiotic factors that prevent the continuous growth of a population. Because of limiting factors, the number of organisms in a population is often well below carrying capacity.

Populations The rate at which a population grows can be calculated. Four factors that are part of the growth rate equation are births, deaths, immigration, and emmigration.

Rate of Population Growth Equation Formula Rate = (# of Births + # of Immigrants) – (# of Deaths + # of Emmigrants) Extremely fast growth in a population is called a Population Explosion. Reasons for a population explosion are… New species introduced to an environment with few predators. Plentiful food supply. Abundant space.

An Alien Species is the term for the introduction of a foreign species to a new environment. Two examples in the Great Lakes were the introduction of Zebra Mussels and Asian Carp.

When a greater number of species leave a population compared to the number of species entering the population, this is called population extinction.

Assignment Limiting factors Carrying capacity Population terms Watch March of the Penguins Complete movie questions