Populations – Chapter 5 Population: A group of organisms that belong to the same species and living within a certain area Populations-a group of the same organisms that are the same species and live in the same area at the same time.

Vocabulary Terms Population Density – Number of individuals per unit of area Population Growth – Increase in the size of the group Biotic Potential – Highest rate of production possible under ideal conditions Population Density-number of individuals per unit of area; ex: 4 deer per square mile Population Growth- can be negative or positive, showing the populations can increase or decrease Biotic Potential- reproductive capability over a period of time; ex: elephants are pregnant for 2 years so their biotic potential is low. Most organisms do not live up to their biotic potential because we don’t have ideal conditions.

ZPG When a population stays the same it is said that there is zero population growth. What factors go into determining a growth rate? ZPG- means the population stays the same size

Determining a Growth Rate 1. Movement out of the area - Emigration Movement into the area – Immigration 2. Number of organisms born – Birth Rate Number of organisms that die – Death Rate Emigration and Death rate increasing together means the population will decrease. Immigration and Birthrate increasing together means the population will increase.

For ZPG to occur: Birthrate + Immigration = Death Rate and Emigration

Populations are Changing!! Exponential and Logistic Growth Patterns

Trend #1: Exponential Growth J-Shaped Curve Ideal environmental conditions There are no limiting factors holding this population back!! Ex) lots of food and water and space Population reproduce at a constant rate This curve is not realistic because conditions are not ideal anywhere.

Trend #2: Logistic Growth S-Shaped Curve Logical Growth Limits on population size based on resources, Limiting Factors, are present The first have looks like exponential growth, but it starts to flatten out because resources in any population such as food, water, reproductive (biotic) potential, space are limited. An area can only maintain so much individuals and remain stable, but not all organisms can survive and reproduce. An area can only maintain so much and remain stable.

Found only in logistic growth. Means the number of organisms an ecosystem can maintain over time Carrying Capacity When organisms have reached their carrying capacity, which is the maximum number of organisms an environment’s resources can support, it at first overshoots it, and then drops below and then overshoots it, and then drops below and so on.

What happens if the population goes over carrying capacity? The population crashes This population exceeded its carrying capacity (so it got too big) and they died out drastically because they ran out of resources or either disease came in.

Graphing Population Trends Now: Create a graph of the chipmunk population from 1940 to 1995. Remember to label the x and y axis. Time always goes on the _______!! Give it a title! We did not do this slide.

Realistic Growth In the real world there are limiting factors that eventually come into play as a population gets larger. The are called limiting factors because they limit the growth rate of a population. This limit causes the population growth to level off, meaning that the population will reach carrying capacity. Limiting factors aren’t in play on the exponential part of the s curve, but show up when organisms reach their carrying capacity.

Carrying Capacity

Factors which cause carrying capacity Density Dependent: Do not affect all populations the same. Ex) Food, Space, Mates, Disease, Predation Density Independent: Affect all populations the same despite population size. Ex) Natural Disaster (Flood, Drought, Fire), Pesticides or Poisons, Destruction of Habitat Density Dependent Limiting Factors- means that these factors will limit the population of organisms because they are too crowded; ex: food, water, space, mates, disease, predators. Disease and predators are limiting factors because the more organisms are in the population, the closer they are together, and the easier it is to spread the disease or the predators to catch prey if the organisms are crowded in too closely (more dense population in an area). Density Independent Limiting Factors- means that these factors will limit the population of organisms whether the population is crowded or not; ex: storms, drought, fire, poisons. It doesn’t matter how big or crowded or close together the organisms live with each other because a flood will destroy any size population.

Rabbit Island Scenario 1: Small Island of 5 Rabbits Climate - Food supply - Predation - Scenario 2: Small Island of 500 Rabbits Climate – Food Supply – Scenario 1: Small Island of 5 Rabbits Climate- yes this impacts population size- density independent Food supply- no doesn’t impact population size- density dependent Predation- yes this impacts population size- density dependent Scenario 2: Small Island of 500 Rabbits Climate- yes this impacts population size- dependent independent Food Supply- yes this impacts population size- density dependent Predation- No this does not impact population size- density dependent If the answer changes based on the size of the population then it is density dependent. If it does not, it is density independent.

Summary of Scenario Which ones changed based on the population size? Food Supply and Predation (These are Density Dependent) Which ones stayed the same? Climate (This is density independent)

April to November – Steady Population Increase November to December – Drastic Increase in Population Size (Exponential Growth)- plenty of resources here December to January – Drastic Decline in Population Size (Population crashed because they exceeded carrying capacity)- they used up all their resources January to April – Slow Decline, even though population is starting to stabilize again.

Summary Questions How do you explain the exponential growth pattern in the beginning…what factors affected this growth? How do you explain the then drastic decline? Abundance of Resources in the beginning, might be reproduction time! Decrease in resources, change in temperature, end of life cycle