POPULATION GROWTH 3 things contribute to population size 1.Number of births 2.Number of deaths 3.Number of individuals that enter or leave Immigration Emigration

Populations group of organisms of the same species living in the same ecosystem. As living organisms, the ecosystem must provide Enough energy Space for shelter Mates for reproduction

When conditions are favorable the number of offspring produced increases exponentially. Growth doubles regularly within a given period of time.

Exponential growth is time limited. Does not continue for any length of time. Is not indicative of natural growth. So why does it happen: Problems:

Logistic growth is more realistic. Basically more offspring are born initially than those that die. Continues until changes affect ecosystem and/or population. Birthrate Deathrate

Logistical population growth occurs in 5 stages: 1. Species is introduced into a community. Niche is established. 2. exponential growth begins. Why? Birthrate? Deathrate? 3. Population continues to grow but at a slower rate.

4. As niche is further established, growth continues to slow. Birthrate? Deathrate? 5. Steady state. Average growth rate=0 0 means there will be some fluctuation but not a continual rise as seen in step 2. BR begins to equal DR.

Carrying capacity: Exponential growth Carrying Capacity

Remember limiting factors--- extinction overpopulation food supply space mate

Which is less dense? Which allows for more growth? Which has less competition? Which will limit growth?

Density-Dependent Limiting Factor- The rate at which a population can grow is dependent on the number of individuals living in that community. Is observed in large populations rather than smaller ones. Will lead to--

Competition: overpopulated species compete for food, space, sunlight, water, oxygen, minerals/nutrients w/in same species: DDLF w/different species: compete to decrease competition – ecology and evolution competition natural selection

Predation: predator / prey relationship predator # = prey # steady balance predator # prey # eat more prey than are born--# of prey decreases Prey DR increases faster than BR This would result in… a.Lack of food for predator b.Predator # drops, allows prey to recover

Prohibited species-introduced into eco- system, not native, grows exponentially for a long time because there is no natural predator. Wrecks havoc with community. Evolutionary fix: prey- new defenses predator-changes in metabolism and structure

Symbiosis: special relationship between predator and host. Mutualism: both benefit Commensalism: predator benefits/host not affected Parasitism: predator benefits/host injured high density communities allows for: 1. easy travel 2. large number of hosts available

Crowding and stress: each species requires specific territory. number of territories available = DDLF Overcrowding leads to- Competition fighting stress changes In endocrine and immune systems of Species affected changes in BR

Density-Independent Limiting Factor: the number of individuals is not a limiting factor to the growth of the population. Outside factors limit growth- a. Disease b. Weather c. Climate change Cause population to grow then fall

DDLF and DILF work together Some questions to consider— 1.Why would populations change over? 2.Human population grew exponentially about 500 years ago. Why? 300 years ago? 3.Why do populations in underdeveloped countries continue to grow exponentially while the rest of the world is at the steady state?

Demographics and age structure diagrams: Demography=scientific study of human growth and populations. 1. birthrate 2. death rate 3. age structure

Demographic transition=a dramatic change in birth and death rates. A B C D As both BR and DR change, population growth eventually evens out. DT reaches completion when BR falls to meet DR and population growth stops. *

Age Structure: actual numbers of individuals in a population not the only factor in population growth. Age plays a key factor in growth. When a large % or a population is young, exponential growth will continue. When a large % of a population is old, there is a different concern.

Human population growth 500 years ago… What part in this growth will economics, science, medicine, conservation play in controlling the growth?