Unit 1.3 Investigating Population Growth

Define habitat

An area with a particular set of features

When picturing a habitat, what 2 aspects are required to make up the scene?

Physical (abiotic) and biological (biotic) aspects

Are habitats define by either physical or biological characteristics or both?

Both

Give an example of a chimps habitat and a BC cedar tree habitat

Habitat for a chimp would be tropical with fruit trees; BC cedar tree habitat would be wet, warm, and full of moss

Give a linear imaginary example of what could happen if a small population moved to a new region across the world

Population would adapt; could hurt/tax/enrich the environment; may be too much food or not enough, may have to change eating habits and hunting patterns; invasive species may directly or indirectly hurt humans; may overcrowd area; may overeat foliage; could help humans flourish or impair them

Can a population in nature remain unchanged?

No, not for long

Population size is always changing due to what 4 human factors?

Natality, immigration, mortality, and emigration

What does it mean if a population is “open”?

Population can be changed by immigration or emigration; there are no barriers preventing people from coming in or out of the area

What does it mean if a population is “closed”?

Population not changed by immigration or emigration; area separated by long distances or physical barriers

An island in the middle of the ocean is an example of an open or closed population?

Closed

A moose in Northern Ontario is an example of an open or closed population?

Open

Define net population/population dynamics

Change in population size after combined effects of births + deaths + immigration + emigration

What is the equation to find the net population?

(b+i) - (d+e)

What is the equation for percentage change in population?

(b+i) - (d+e) / N X100%

Population dynamics of a species is the result of the interaction between what 2 kinds of factors?

Internal and external factors

What is 1 example of an internal factor?

Reproductive ability

What are 4 examples of external factors?

Weather, food supply, predation, disease

Are all populations the same in terms of their cycles (i.e. stable, up, down)?

No. Some stay stable while others fluctuate dramatically

Populations are simultaneously affected by what 4 things?

Population density, amount of resources available, the environment, interactions with other species

Define population ecology

Area of biology that studies how populations change overtime in reaction to their environment and other species

Who or what impacts all species on the planet?

Humans

Why are population models useful?

To see how populations respond to changes in various input factors. Made up of equations that describe how a population will respond to changes in both internal and external factors

What are the 3 fundamental population growth models?

Geometric, Exponential, and logistic

What population is the geometric growth model best?

Where individuals breed only once per time period (ex: deer only give birth late spring/early summer); or if the birth/death rates per individual remain constant then the population growth rate is constant over a fixed time period

What would be a good population for the geometric growth model?

Bacteria

What is the equation for the geometric growth model?

λ = N(t+1)/N(t) where lambda is the fixed growth rate, N(t+1) is the population size at a time 1 unit after N(t), and N(t) is the population size at a particular time

For what type of population is the exponential growth model best?

For populations that can reproduce any time of the year (ex: humans). Population can grow continuously not being restricted by fixed time periods

Which shows a steeper increase in population- geometric or exponential growth model?

Exponential growth model

What is the equation for instantaneous growth?

dN/dt (instantaneous growth) = rN where r is the growth rate per individual and N is the population size

Why is rN (growth rate per individual X population size) called “instantaneous growth rate of the population”?

Tells us how much the population size is changing at any particular instant in time

Define biotic potential

With unlimited environmental resources, the value of r (growth rate per individual) reaches its maximum; OR max population growth rate that could occur under ideal conditions for an organism

Why is the logistic growth model “last” of the 3 types?

A population will inevitably run out of food or space and the growth rate will change shape- become the logistic growth model

Which of the 3 growth models most closely resembles what happens in natural populations?

Logistic growth model

Describe what happens to a population in the logistic growth model

New population starts small; lots of resources so grows fast like in the first two models; slows down because resources deplete; population stabilizes near its carrying capacity

What letter does a logistic growth model look like on a graph?

S

What is the S shape on a logistic graph called?

Sigmoid

What are the 3 phases of the logistic growth model called?

Lag, log, stationary

What is the equation for the logistic growth model?

dN/dt (instantaneous growth) = rN (K-N)/K where N is the population size at time t, r is the growth rate per individual, and k is the carrying capacity

In the logistic growth model, as the population size gets closer to the carrying capacity, what number is the instantaneous growth rate closest to?

0

What is something useful to remember regarding the logistic growth model?

It accounts for the fact that resources are always finite

What is negative about the logistic growth model?

Assumes amount of resources remain constant but in reality they vary in nature- space, food, new species, competition, extreme weather, fire, flood

What 2 factors is carrying capacity determined by?

Internal and external factors

What is another name for internal factors?

Density-dependent factors

What is another name for external factors?

Density-independent factors

Define density-dependent factors

Factors that affect a population’s growth rate because of its density

What happens to density-dependent factors as density increases?

They intensify

What are 7 density-dependent factors?

Predator focus, resource availability, aggression, emigration, waste accumulation, disease, and stress

Define “predator focus” density-dependent factor

Predators go after most common prey; higher prey density means more predator pressure means higher mortality

Define “resource availability” density-dependent factor

Higher density means must share resources means more effort into protection means lower birth rates and higher mortality

Define “aggression” density-dependent factor in mice

Higher density (in mice) lead to anti-social behaviour and aggression to own species

Define “emigration” density-dependent factor

Higher density means some may leave which means lower population

Define “waste accumulation” density-dependent factor

More poop and urine means pollution

Define “disease” density-dependent factor

Higher density means sickness and parasites can spread more quickly

Define “stress” density-dependent factor

Higher density means more stress means weakened immunity and other health problems

Define density-independent factors

Factors that affect population growth unrelated to density

Give 5 example of density-independent (abiotic) factors

Extreme weather, fire, drought, volcanic eruption, pollution

What population is very susceptible to density-independent factors?

Insects. Cold weather kills; warm weather skyrockets their population

The invasive Japanese Beetle is a good example of what?

Density-independent factor. Milder winters due to climate change mean they don’t die which mean they are laying many eggs on trees in Western Canada and killing the trees

Do all populations follow expected trends?

No. Go through a cycle with dramatic highs and lows over a regular time period

What population cycle is observed in Forest Tent Caterpillars?

Species with high fecundity. Experience 10 year population cycle; peak lasts 2-4 years. Why? Best guess is weather, predation, parasites

Can a population trend involve more than one species affecting one another? If yes, who is it often seen between?

Yes. Predator ← → main prey

Describe the population cycle and 2 main factors between hares and lynx’s

Population peaks on 10 year cycle. Main factors are food supply and predation.

What are the 3 phases in the relationship between hares and lynx’s?

Increasing, peak, and decline

What happens in the “increasing” phase of the hare/lynx relationship?

Hare’s density is low; more food; more births; number of lynx’s is low (low predator numbers)

What happens in the “peak” phase of the hare/lynx relationship?

High food; low predation; but as density increases so does mortality; means lower reproduction; less food; more social stress; lynx have lots of food but lynx only give birth in the spring so their population isn’t increasing

What happens in the “declining” phase of the hare/lynx relationship?

After peak is reached, rapid decline because no food and more predators; less hares means lynx’s starve, disease, mortality increases, lower fecundity. Lynx population decreases but only after the hare’s population has decreased first

Why does the population cycle of the lynx lag 1-2 years behind the hare?

Because they only give birth once per year in the spring. Hare population starts to decrease but at the same time more lynx’s are not being born