Factors Affecting Population Change

14.3

Review:

How did the introduction of zebra mussels affect the health of the Illinois River?

What is a density-dependant factor?› ___________ and ____________ recognized the

struggle for available resources within a growing population would inherently _____________ population size.

› Examples: ___________________, _________________, _____________________.

What is intraspecific competition?› As density increases, there is more

______________ among individuals. › At carrying capacity, _____________

individuals will survive whereas the ______________ individuals will starve or risk death by moving areas.

› Building roads?

Less resources?› Decrease in individual’s growth/reproductive

success. › Harp seals: reach sexual maturity at 87% body

weight if not enough food, slower sexual maturity decrease fecundity.

Predation?› Many prey go for larger populations easier to

catch. › Predators regulate population. How?› How have caribou populations been disturbed

by humans? need to share habitat with wolves.

Disease?› Why? pathogens able to pass from host to

host with greater ease › Overcrowding.

Low density?› All plant and animal species suffer

decrease in per capita rate of increase as populations reach small sizes or low densities.

ALLEE EFFECT. Finding mates, social interactions requiring high

densityEx// passenger pigeon: hunted. Declined in numbers.

could only lay one egg per nest last one died in 1914.

Therefore, harder for pop. To recover with species with low fecundity.

Small population› Results in inbreeding and loss of genetic

variation.› Minimum viable population size?

Smallest number of individuals that ensures the population can persist for a determined interval of time. So pop can cope with variations in natality and

mortality, environmental changes and disasters. Used to figure out which species at risk.

What are density- independent factors?› Changes in size not related to population

density Human intervention, weather changes,

disasters.› Ex// thrips: small insect: consumes many

different plant species that food supply is not a limiting factor. Do no breed in cooler temperatures Regardless of population density

Biomagnification

Increase of a substance throughout a food-chain.› One predator consumes 100 prey which

consume 10,000 blades of grass EACH which was treated with DDT.

Limiting Factors...

Prevent populations from achieving their biotic potential.› What was this again? Biotic potential: the maximum rate a population

can increase under ideal conditions.› Limiting Factor: any essential resource

that is in short supply or unavailable. Determines how much an individual or

population can grow. Ex// a plant requires nitrogen, CO2, and sunlight for

growth. If all other factors are available, but nitrogen is used up, N is the limiting factor.

Overshooting the Carrying Capacity

Too many births/immigration may result in population overshooting its carrying capacity. › When pop. Surpasses carrying capacity of

habitat, d> b = population decrease.

Interactions within Communities

14.4

Community

All populations in a given ecosystem at a given time› Interact with each other directly or

indirectly.› Some organisms cannot exist

independantly of one another Ex// flowers/insects.

Ecological Niches

Ecological Niche: an organism’s biological characteristics, including use of and interaction with abiotic and biotic resources in its environment.

Fundamental Niche: › Biological characteristics of an organism and the set of

resources that individuals in the populations are theoretically capable of using under ideal conditions.

However, organisms face interspecific competition with other organisms which use the same resources.› Interspecific competition: BETWEEN SPECIES.

Realized Niche: › (ex// a lion may compete for food with vultures and hyenas)› The biological charatceristics of the organism and the resources

individuals in a population actually use under the prevailing environmental conditions.

Types of competition within a community (review)

Intraspecific: b/n individuals of same species

Interspecific: b/n individuals of different species.

5 Ways to Classify Interactions b/n species within a community...

Symbiosis: various interactions in which two species maintain a close, usually physical, association; includes parasitism, mutualism, and commensalism.

Interspecific Competition

Between individuals of different populations.› Restricts population growth.

Interference competition actual fighting over resources › Tree swallows + bluebirds for birdhouse

Exploitive competition consumption or use of shared resources. › Two predators rely on same prey (arctic foxes

and snowy owls both prey on same pop. Of arctic hares)

Gause’s Principle

1934 “The Struggle for Existence” Two species with similar requirements could not

coexist in the same community.› The more niches that overlap, the greater the

competition. › One species consumes most of the resources,

reproduces more efficiently inevitably drive other species to extinction.

› CONCLUSION: if resources are limited, no two species can remain in competition for the same niche indefinetely.

› COMPETITIVE EXCLUSION

Interspecific Competition (Con’d)

Resource Partitioning (Animals)› Individuals of the same species avoid competition for similar

resource› Ex// birds or lizards (of same species) occupy different

perching/nesting/eating sites.› Reduces interspecific competition

Increases likelihood of species surviving. Resource Partitioning (Plants)

› Annual plants: foxtail, mallow, smartweed› All require similar nutrients from the same habitat› Each evolved unique ways to survive in the presence of each other

Foxtail: shallow, fibrous roots absorbs water from surface of soil Mallow: deep taproot system grow deeply down into soil/obtain

moisture later in growing season Smartweed: branches both in the topsoil and soil below the roots of

other plants: “best of both worlds”

Predation

Interspecific interaction why? When prey population increases,

predator population can increase why?› Reduction of prey results in a decline in

predator population... Unless it has access to another food source.

Cyclical patterns of predator-prey relationships

Two species cycle slightly out of synchronization› Predator lags behind prey

Describe what is happening at Time:A)B)C)D)E)

Defence Mechanisms

Prey have adapted unique ways to detour predators› Thorns, hooks, spines, needles, chemicals

(plants) Mustard family (pungent odour) Balsam fir (chemicals that mimic an insect

growth hormone when linden bugs feed on balsam fir, remain in juvenile stage and eventually die) How would this help the balsam fir?

Defence Mechanisms (2) Monarch Butterfly

› Consumes toxins (not toxic to itself) is distasteful to its predators. Butterflies start out as caterpillars (ie. larvae)

feed on milkweed through metabolism milkweed becomes unpalatable.

Blue jays don’t ‘finish’ eating monarch butterflies.

Defence Mechanisms (3)

Passive or Active› Passive: hiding

Camouflage (cryptic colouration) Bright colours: warn predators of chemical

defence mechanisms (poisons) Monarch butterfly Wasp (hover fly?) Lethal octopus, Haplochlaena maculosa: pattern

(rings) contract and expand as warning signal.

› Active: fleeting Alarm calls to mob the predator

Different types of defense mechanisms

(Are the animals ‘meaning’ to do this?)

Defense Mechanisms (4)

Mimicry› Mimic resembles distasteful/harmful species› Batesian

Palatable/harmless species mimics unpalatable/harmful organism

Ex// Viceroy butterfly monarch › Mullerian

Several unrelated species that resemble one another and are all poisonous/dangerous. “pooling of numbers` causes predators to learn

more quickly to avoid these species.

Independent Reading

Read pages 684-687 (Symbiosis & Disruption of Community Equilibrium)› Define/understand all of the definitions:

Mutualism, commensalism... Macroparasites, etc.

› Relate definitions to example species (in text)

Seatwork/Homework

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