Populations and Communities Flashcards

Carrying Capacity: the maximum population size of a species that can be sustained (long term) by a given environment

Limiting Factors:

Limiting Factors: environmental factors that restrict the growth, distribution, or abundance of a population or organism w/in an ecosystem

• EX: availability of food/water

• EX: space

• EX: shelter

• EX: disease/parasites

• EX: predators

• EX: climate

Density-dependent limiting factors: have a greater impact on population size as the population density increases —> due to an increase in inter/intra-specific competition

Interspecific Competition: competition between organisms of different species

Intraspecific Competition: competition between organisms of the same species

Identify several density-dependent limiting factor AND explain why they’re density-dependent:

• competition for resources

• predation

• disease/parasites

State what size population density-dependent limiting factors maintain

• they keep the population size around the carrying capacity

Density-independent limiting factors: have an impact on population size regardless of its density

• external factors that cause drastic changes (typically abiotic)

• EX: Natural disturbances —> floods, droughts, hurricanes, earthquakes, volcanic eruptions

• EX: Anthropogenic Events —> habitat destruction, pollution, climate change

  • anthropogenic: environmental change caused or influenced by people, either directly or indirectly

Population Growth Curves

Exponential Population Growth:

• exponential growth curves are J-shaped

• exponential growth occurs in ideal conditions —> unlimited resources, biotic & abiotic factors are favorable

  • EX: bacterial growth in lab

State how exponential growth relates to carrying capacity in natural ecosystems:

• In ecosystems, limiting factors are present —> prevents unlimited exponential growth

• Exponential growth typically only occurs when the population is well below the carrying capacity

American Plains Bison exemplifies exponential growth:

• hunting decimated the American Plains Bison in Yellowstone

• In 1902, there were only 21 bison that remained

• by 1915, bison numbers were up to 250

Sigmoid Population Growth:

• S-shaped curve

• occurs in environments with limited resources

3 Phases in a Sigmoid Growth Curve:

1. exponential growth phase

2. transitional phase w/ environmental resistance —> as population grows, density dependent factors increase & growth slows

3. plateau phase —> eventually reaches equilibrium around the carrying capacity

Population Growth Factors:

List & Define 4 Factors that Impact Population Growth:

1. Natality (N) = birth rate

2. Immigration (I) = individuals entering population

3. Mortality (M) = death rate

4. Emmigration (E) = individuals leaving a population

Equation that represents change in population (population growth) using 4 the factors:

Population Growth = (N + I) - (M + E)

Natality & Immigration is GREATER THAN Mortality & Emmigration:

• N + I > M + E

• population size increases —> positive population growth

• Identify the growth phase if N+I is significantly greater than M+E

  • the population is likely in the Exponential Phase & the population is rapidly growing

• Identify the growth phase if N+I is slightly greater than M+E

  • the population is likely in the Transitional Phase & the population is growing slowly

• Identify the reason for slower growth in the transitional phase

  • slower growth due to density-dependent limiting factors

Natality & Immigration is EQUAL TO Mortality & Emmigration:

• N + I = M + E

• population size is constant —> 0 population growth

• Identify the growth phase if these are equal

  • Plateau Phase

Natality & Immigration is LESS THAN Mortality & Emmigration:

• N + I < M + E

• population size is decreasing —> negative population growth

Intraspecific Interactions:

Intraspecific Interactions: interactions between organisms of the same species

• includes competition & cooperation

Intraspecific Competition: organisms of the same species compete for the same limited resources (food, shelter, mates)

• density-dependent limiting factor

Intraspecific Cooperation: individuals collaborate to increase their chances of survival & reproduction

• EX: group hunting/foraging, defense against predators, shared parenting

Community: a group of interacting species in a particular area

• communities will have intraspecific AND interspecific interactions

Interspecific Interactions:

Interspecific Interactions: interactions between organisms of different species

• Herbivory, Predation, Interspecific Competition, Symbiotic Relationships

• Herbivory: feeding relationship —> herbivore eats plant material

  • EX: giant panda eating bamboo

  • EX: parrot fish eating algae on coral reefs

• Predation: feeding relationship —> predator captures & consumes its prey

  • EX: grizzly bears & salmon

  • EX: wolves & deer

  • density-dependent limiting factor

Cycle of predator-prey relationships: cyclical pattern of population increases & decreases

• as prey numbers increase, predator numbers increase & the prey experience increased predation (reduced prey numbers)

• less prey = less food available to predators & predator numbers drop

• less predators = increased prey population

• “Lag Time” in Predator-Prey Relationship Graph

  • predator numbers increase/decrease slightly after prey numbers increase/decrease

Interspecific Competition: competition between different species for the same limited resources

• Eastern grey squirrel and American red squirrel compete for food

• you can test for interspecific competition by removing one species from the ecosystem

  • if the 2nd species is more successful, this suggests that there’s interspecific competition

Symbiotic Interactions: 2 organisms living and interacting closely w/ each other where at least 1 organism benefits

• Parasitism, Commensalism, Mutualism

Parasitism: one organism (parasite) is helped & the other organism (host) is harmed

• +/-

• EX: tapeworms living in a human gut

• parasites have evolved to minimize damage to host in order to keep the host alive longer

• Pathogen: a microorganism (bacterium, fungus, protista) or virus that causes disease in a host

• Parasitism v. Pathogenicity: pathogenicity is different from parasitism because the host is normally directly & immediately harmed & can spread more rapidly

Commensalism: one organism is helped & the other is neither helped nor harmed

• +/0

• EX: orchids growing on the branches of trees

• EX: sharks and remoras (sucker fish)

Mutualism: both organisms are helped by the relationship

• +/+

• EX: Root nodules in Legumes: nodules contain nitrogen-fixing bacteria

  • bacteria provide the legumes w/ usable nitrogen

  • Legumes provide bacteria with carbohydrates & other organic matter/compounds

• EX: Mycorrhizae in Orchids: fungi colonize orchid roots & form Mycorrhizae

  • fungi increase surface area for nutrient absorption in the soil

  • orchids provide the fungi with organic compounds produced during photosynthesis

• EX: Zooxanthellae in hard corals: Zooxanthellae are unicellular photosynthetic algae that live w/in the tissues of hard corals

  • Zooxanthellae provide corals w/ organic molecules made during photosynthesis & pigmentation to protect from UV exposure

  • corals provide the zooxanthellae a sheltered environment and easy access to sunlight

Invasive Species:

Endemic species: native to the location

Introduced species: non-native & were introduced by humans

• AKA alien species —> can be accidental or deliberate

• not all introduced species become invasive

  • EX: potatoes brought to Europe from Peru

• an introduced species becomes invasive when it causes harm to the ecosystem & outcompetes native (endemic) species

  • can cause a decline in endemic species bc they rapidly increase in the number and are more efficient in resource use

• EX: Lionfish in the Carribean

• EX: Kudzu in Georgia

  • Kudzu is native to Japan & southeast China and was introduced to the U.S. as an ornamental plant/tool to prevent soil erosion

  • grows extremely quickly & outcompetes native species by shading native plants (preventing photosynthesis)

Top-down Control:

Top-down Control: when the presence & activities of organisms at higher trophic levels regulate the abundance or behaviour of lower trophic levels in a food chain

• EX: Grey Wolves in Yellowstone: the reintroduction of them caused a trophic cascade

  • wolves impacted many trophic levels w/in the ecosystem

Bottom-up Control: availability of resources at lower trophic levels influences the abundance & distribution of organisms at higher trophic levels

• soil nutrient availability as an EX of bottom-up control:

  • it determines growth of plants which determines herbivore numbers which determines predator numbers —> another type of trophic cascade

• both types of control are present in most ecosystems, however, normally, one tends to be the more dominant type of control

Allelopathy: organisms release biochemical compounds into the environment, influencing the growth, survival, or reproduction of other organisms in the area

• EX: black walnut trees produce toxic chemicals from the roots & sensitive trees nearby are injured or killed

Describe an example of Antibiotic Secretion:

• some microorganisms (fungi/bacteria) can secrete antibiotics to hinder the growth of bacteria

  • Penicillium mold naturally produces the antibiotic penicillin

• EX: Streptomyces bacteria, commonly found in soil & marine environments, have the ability to synthesize a wide range of antibiotics, including streptomycin