Populations Chapter 8

Population Definition – all the members of a species living in the same place at the same time. Species – What? Place – Where? Time – When?

We can describe a population in terms of 3 things: 1. Size – how many individuals (actual numbers) Change in Population size Population + (Births – (Death = population & Immigrants) & Emmigration) size (into [increase]) (exit [decrease]) 2. Density – number of individuals per unit area 3. Dispersion – how the individuals in a population are arranged within an area.

Population continued… 3 Types of Dispersion 1. Even (trees or plants) 2. Clumping – not evenly distributed 3. Random – no pattern 3 Types of Population change 1. Positive – population goes up 2. Negative – population goes down 3. Zero – population remains unchanged

Population continued… Reproductive Potential The maximum number of offspring that each member of a population can produce. Characteristics of Population with a high reproductive potential 1. small in size 2. reproduce early in life 3. large litters 4. give little to no parental care

Population continued… Exponential Growth When a population grows faster and faster; the bigger the population gets. It forms a “J” shape curve when graphed See Figure 4, Page 213 It will only occur when populations have plenty of food and space – have little or no competition or predators. Very rarely occurs in nature.

Population Change & Exponential Growth

Population continued… Limits to population growth 1. Predators 2. Disease 3. Competition 4. Climate 5. Food Limiting Resources – all of the above help to maintain the carrying capacity of an ecosystem. Carrying Capacity – maximum population an ecosystem can support at any given time.

Carrying Capacity

2 Types of Population Control 1. Density dependent – more deaths occur the denser the population is  examples of density dependent causes of death include:  limited resources  predation  Diseases Examples: flu, plague, famine, etc.

2. Density Independent – a certain number of individuals will die regardless of the population.  examples of density independent causes of death include:  Natural disasters  Severe weather examples: floods, fires, earthquakes, etc.

Section 2 - Species Interaction Niche – organisms unique role in an ecosystem All organisms have one Species Interactions 1. Competition – when 2 species or 2 members of the same species want or need the same resources. 1 species or 1 individual always loses out It negatively affects both species

2. Predation – predator/prey relationship Predator benefits because it gets food. Prey is harmed because it is killed (individual) The prey, within a species, is benefited because its population is controlled and weak members are eliminated.

3. Parasitism – (parasite/host relationship) parasite is an organism that lives in and feeds off a host. The host is the organism the parasite lives in. Parasite is benefited because it gets a habitat and food. The host is harmed. Parasite – benefits Host - harmed

4. Mutualism – 2 species having close interaction and each does something for the other. (ex. Clownfish & Sea anemone) Both species Benefit – clownfish attracts fish for sea anemone to eat and sea anemone habitat protects clownfish

5. Commensalism – 1 species benefits while the other is neither harmed or helped. ex. Birds & trees: birds get protection & home & trees are just there

Relationships #1-5 are types of symbiosis Symbiosis happens when 2 species live in close contact with each other. Coevolution – when 2 species who live in close interaction evolve together. A change in 1 species causes the other to have a change as well

Species Interactions