POPULATION GROWTH

3 things contribute to population size1. Number of births2. Number of deaths

3. Number of individuals that enter or leave

ImmigrationEmigration

Populations group of organisms of the same species living in the same ecosystem.

As living organisms, the ecosystem mustprovide• Enough energy• Space for shelter• Mates for reproduction

When conditions are favorablethe number of offspring producedincreases exponentially.

Growth doubles regularlywithin 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. Basicallymore offspring are born initially than thosethat die. Continues until changes affectecosystem 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 growis dependent on the number of individualsliving in that community. Is observed in large populations ratherthan smaller ones.

Will lead to--

Competition: overpopulated species compete for food, space, sunlight, water, oxygen,

minerals/nutrientsw/in same species: DDLFw/different species: compete to

decrease competition –ecology and evolution

competition natural selection

Predation: predator / prey relationshippredator # = prey # steady balance

predator # prey # eat more preythan are born--# of

prey decreasesPrey DR increases faster than BR

This would result in…a. Lack of food for predatorb. 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 betweenpredator and host.

Mutualism: both benefitCommensalism: predator benefits/host

not affectedParasitism: predator benefits/host injured

high density communities allows for:1. easy travel2. large number of hosts available

Crowding and stress: each species requiresspecific territory.

number of territories available = DDLF

Overcrowding leads to- Competition fighting stress changesIn 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. Weatherc. 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 exponentiallyabout 500 years ago. Why? 300 years ago?3. Why do populations in underdeveloped countries continue to grow exponentiallywhile the rest of the world is at the steadystate?

Demographics and age structure diagrams:

Demography=scientific study of human growth and populations.1. birthrate2. death rate3. age structure

Demographic transition=a dramatic change in birth and death rates.

A

B

C

D

As both BR and DR change, population growtheventually evens out. DT reaches completion whenBR falls to meet DR and population growth stops.

*

Age Structure: actual numbers of individuals in a population not theonly factor in population growth.Age plays a key factor in growth.

When a large % ora population is young,exponential growth willcontinue.When a large % of apopulation is old, there is a different concern.

Human population growth

500 years ago…

What part in this growth will economics,science, medicine, conservation play incontrolling the growth?