Evolution and Populations How Populations Change

Populations Populations are made of members of the same species living in the same area at the same time Members of a population mate with each other and produce fertile offspring. A population interacts with populations of other species. This interaction creates a community.

Ecological Populations Biosphere – All of the ecosystems of the Earth. Ecosystem – The community plus abiotic factors such as climate Community – Many species interacting Species – able to breed and produce fertile offspring. Organism – made of many organ systems.

Population Characteristics Three important characteristics of populations are its: Geographic distribution (range) Density (#/area) And growth rate

Population Growth Populations can decrease from emigration (organisms leaving the area – Remember “E” for Exit) and deaths.

Population Growth Populations change from year to year. Populations can increase from immigration (organisms moving into an area- Remember “I” for In) and from births.

Population: Exponential Growth When food and space are plentiful, populations can grow quickly; sometimes doubling rapidly. This type of growth is exponential growth. Grasshopper plague in Africa

Population: Exponential Growth Under ideal conditions with unlimited resources, a population will grow exponentially. It means that more of the population will survive than dies. Exponential growth is represented by a J- curve graph.

Population: Logistic Growth Exponential growth does not happen in natural populations for very long because the resources get used up. Population growth slows down when food and space become more difficult to find.

Population: Logistic Growth When populations grow exponentially but begin to slow when resources are used up, it is known as logistic growth. Logistic growth is represented by an S- curve graph.

Population: Logistic Growth As the growth curve slows down and flattens out, it is said that the population has reached “carrying capacity”. Carrying Capacity

Population: Logistic Growth Carrying capacity is the maximum number of organisms that can be supported by an environment. Carrying capacity changes based on the abiotic and biotic factors in the environment.

Please label your graph! Mark the exponential growth section. Mark the section of slowing growth. Draw in the carrying capacity line.

Limiting Factors Limiting factors are factors that cause a population to decrease. Limiting factors can include nutrients, space, predators, and temperature.

Limiting Factors Density-dependent limiting factors only affect LARGE populations. These factors include disease, predation, competition, and parasitism.

Limiting Factors Density-Independent Limiting Factors impact all populations no matter what their size. These factors include natural disasters, weather, and seasonal cycles.

Evidence to Support Evolution by Natural Selection Scientists have been able to support the Theory of Natural Selection by finding evidence in: Fossil records Homologous structures DNA

Evidence to Support Evolution by Natural Selection While the main idea of evolution through natural selection is from Darwin, it has been adjusted by other scientists. As scientists developed new technology and found new evidence, the original theory had to be changed in order to include the new evidence. DNA Strand

Convergent Evolution: Adaptation to Similar Niches and Environments Often times, animals that live in similar habitats develop similar adaptations even though they are not related to each other. For example: sharks and dolphins have similar body shapes and coloration

Convergent Evolution There are other examples as well: Loon live in the arctic Penguins live in Antarctica They both swim underwater and have counter shading, BUT they are not related.