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.