Chapter 8

Understanding Populations

8-1: How Populations Change Size

Describe the three main properties of a population. (slide 3 & 4)

Describe exponential population growth. (slide 6, 7, 11, 12)

Describe how the reproductive behavior of individuals can affect the growth rate of their population. (slide 6 & 7)

Explain how population sizes in nature are regulated. (slide 8)

What is a population?

All the members of the same species living in the same place at the same time.

“reproductive group” or “gene pool” Population refers to the group in general and

to the size of the group Daisies in Ohio, not in Maryland Bass in a lake in Iowa

Properties of populations: Size Density Dispersion

Size Number of individuals in the population

250,000 people in Kalamazoo County (2010 census)

Density Individuals per unit of area or volume

75 deer per square mile

Dispersion Distribution or arrangement

Even – pine trees in rows in a forest; corn fields Clumped – zebras in the savanna; deer herds Random- dandelions in a field; lizards in the desert

Population Growth

Growth rate is calculated using

change in = births – deaths population size

*Also included would be immigrants (in) to the area and emigrants (out) from the area

*Growth rate can be positive or negative numbers; with negative numbers equaling a decrease in population size

Growth Curves Biotic potential = fastest rate at

which a population can grow. This is also called fercundity (max number of offspring that could be produced vs fertility which is number actually produced).

Reproductive potential = max. number that a population can produce. Earlier maturity Larger numbers of eggs Shorter generation time Survival rate

Sea turtle lay >2000 eggs, they don’t all survive

A pair of elephants could produce 19 million descendants in 750 years….but have one at a time, gestate 20+ months, nurse 4+ years, 15 when mature, raise 1 at a time; even if live to be 100 – only have a couple kids

Bacteria and insects have very short generation times.

Average generation time for humans is 20 years

Limits to population growth Resources are never unlimited or constant; they are either used

up or they change. A limited resource is something the species needs and

consumes at the same rate its produced. Leads to competition

Carrying capacity = theoretical limit to populations size in a given ecosystem. Rabbits in Australia Islands make good studies because of boundaries

Regulation Density dependent – rate of death is worse when

individuals are closely packed (infection in pine trees) Density independent – rate of death is not dependent on

numbers of individuals in the area; storms, crops freezing , etc.

8-2: How Species Interact with Each Other

Explain the difference between niche and habitat. (slide 17-19)

Give examples of parts of a niche. (slide 17-19) Describe the five major types of interactions

between species. (slide 14 & 15) Explain the difference between parasitism and

predation. (slide 14) Explain how symbiotic relationships may evolve.

8.2: Population Dynamics

Population – group of similar individuals that are in the same place, at the same time and comprise a gene pool

Species – organisms that are similar enough to interbreed in nature and produce viable offspring. Breed, variety, strain, subspecies, etc.

“dynamic” means in constant motion, always changing, not static.

Births increase population Deaths decrease population If births = deaths then

population is steady, called “replacement rate”

If growth is exponential, then population increases rapidly…. Parents have 2 kids (4) and they each have 2 kids (8), and they have 2 kids (16)….. The sum of population would go like this 2,4,8,16,32….

Population Growth patterns

Logistic – steady (“S”) Exponential – increasing rapidly (“J”) In a new situation, populations have the

potential to increase exponentially, but natural forces like food/resources, predators and space will eventually create a stable level when the population reaches “Carrying Capacity”

Symbiosis In addition to enough food, water, oxygen, sun, space,

mates and other resources – individuals have interactions with other species that impact their survival and reproductive success. Competition (bugs and food)

Can be direct or indirect NOT an example of symbiosis!

Predator – prey (rabbit – lynx) NOT an example of symbiosis!

Commensalism (bromeliads like orchids) Mutualism (acacia/ants, pollinators/flowering plants,

intestinal bacteria) Parasitism (mosquito, lice, leech, tapeworm)

Resource Partitioning

In order to decrease competition some resources are allocated or partitioned to specific species Common examples include birds that specifically

live in the upper branches, lower branches, or interior of the tree so that one tree can house 3 species in their own separate zones

Niche An organism’s unique role within an ecosystem is

it’s NICHE; FUNCTION or job… “grazer”, “pollinator”, etc Physical space + Environmental factors + Interactions

Realized Niche vs Fundamental Niche

Where you actually are vs. anywhere you could be successful

HABITAT= WHERE you live

Humans The human population is also subject to all of the

conditions studied in ecology Resource availability (coal, Al, transportation, Rx)

Material resources, goods and infrastructure including services

Water, air, food Space Waste Pollution Disease/ immunity Genetic impacts “Creativity”

Carrying capacity is hard to calculate due to the number of variables.