C4.1 Populations and Communities

Population (3)

One species living in one area at one time.

Conditions:

All population members are of the same spcies → “Can reproduce fertile offspring”

Other groups of the same species must be reproductivley isolated.

Define reproductive isolation

Repoductve isolation occurs when there is a barrier preventing members of the same population from reproducing.

e.g a river.

Carrying capacity

The maximum population size of a species that an environment can support long term.

Factors that can affect an environments carrying capacity (7)

Food Availability

Water Availability

Shelter

Space

Disease

Predators

Climate

How are factors affecting population growth classified?

Density dependent or Density independent factors.

Density dependent factors (4)

Factors that change a populations growth due to population density.

E.g.

Predation risk

Disease

Competition

Resource competition

Members of the same species reuire the same finite resources to survive and reproduce.

As the population increases competition leads to reduced avaliability of resources. The better adapted individuals are more likley to survive and reproduce.

Risk of predation

Predators target abundnt populations.

High prey populations result in higher predator populations, high predator populations limit prey populations.

Predators typically limit pop.growth of prey.

Disease

High pop. density facilitates the spread of pests and diseases that are spead by contact & vectors.

This can lead to increased mortality and thus decreased death in the population.

Factors determining wether a population size increases or decreases

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Mortality

Immigration

Nativity

Emigration

Explain the population growth curves (2)

Exponential growth:

Occurs in environments with limited competition for resources.

Sigmoid population growth:

Occurs when a species enters a new environment

1-exponential phase: lag phase as individuals introduced to species

2-transitional phase: resources become more limited due to competition as the pop. continues to grow (+Natality, -Mortality)

3-Plateau phase: Carrying capacity is reached due to limiting factors (food, predators, disease, etc.) (Natality = Mortality).

Atp the pop. will oscilate at the carrying capacity.

Define intraspecific competition: why does it occur, what increases it?

Competition for resources between members of the same species.

Members of the same same species have the same ecological niche, thus compete for the same resources, e.g. territory, mates, social dominance.

Intraspecific competition increases due to density dependant factors.

Give examples of intraspecific competition (3)

American Robin - Territory:

Male american robins compete for territory for resting, mating, and food supplies. Females choose males to mate with based on the quality of their nesting site.

Southern Elephant Seals - Mates:

Males fight for dominance over a group of women. Dominant males gain access to females for reproduction.

Chimpanzees - Social Dominance:

Male chimpanzees compete for positions like the “Alpha Male”. Those with higher social status receive preferential access to food and mates,

Define Intraspecific Cooperation: give examples (5)

When members of a species work together towards a common goal, increasing the species access to resources and protection from predators:

-Group Hunting, Group Foraging

-Parenting

Predator defense

Give examples of intraspecific cooperation (3)

Wolves - Group Hunting: More hunting success, all pack members receive food.

Bees - Group Foraging: Cooperate to collect nectar for hive. Waggle dance to indicate good food sources.

Meekrats - Defense: Make alarm calls to indicate danger. Enables safe group foraging.

Orangutangs - Parenting: Females spend nine years teaching their children survival skills.

Define Community

Populations of different species living and interacting together in the same ecosystem.

What are the Interspecific Interactions? (6)

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Hebivorism

Parasitism

Predation

Pathogenocity

Mutualisim

Interspecific competition

Define Herbivoreism, give an example.

The act of eating plants, herbivores are animals that eat only plants.

E.g. Red Deer

Define Predation, give an example.

The act of preying on other animals, predators kill and eat other animals.

E.g. Lions

Define Interspecific competiton, give an example.

When individuals of different species compete for the same resources; Typically leads to competitive exclusion.

E.g. Zebras and Gnus

Competitive exclusion

The differentiation of ecological niches to avoid competition.

Mutualisim

A symbiotic relationship between two species where both individuals benefit.

E.g. Bees and Plants (Dandilions)

Parasitism

A symbiotic relationship where one species benefits but the other species is harmed.

E.g. Tics and Dogs

Commensalisim (not in syllabus?)

A symbiotic relationship where one species benefits and the other is unnafected.

E.g Frogs and Plants

Pathogenocity

Occurs when an organisim infects another species causing a disease.

E.g. Humans and Malarial Parasite.

Give examples of mutualisim (3)

Root Nodules in Fabacae (Legumes), e.g. soybeans

Nodulels have nitrogen fixing bacteria which receives carbs & organic compoiunds, gives nitrogen compounds to plants.

Mycorrhizae in Orchird Roots:

Fungus gives better ability (and surface area) to absorb nutrients, orchird gives fungus protection and carbohydrates.

Zooxanthellae and Corals

Zooxanthellae gives waste removal, nutrients (glucose), and O2, Coral polyps gives protection and CO2 for photosynthesis.

Alien species

Organisims introduced to ecosystems that don’t naturally occur there.

Invasive species

Species that cause harm to ecosystems, often by replacing endemic (native) species by competitive exclusion.

Why might alien species become invasive/outcompete native species? (5)

Absence of predators

Absence of disease

Faster reproductive rate

Bigger size/Agression

Outcompeting for food & other resources

Explain the red and grey squirrel situation in the UK and Ireland. (4)

Red squirels- Endemic

Grey squirels- Invasive

The grey squirrels outcompete the red squirrels because they are larger, stronger, reproduce quicker, and are immune to squirrelpox which plagues the red squirrels.

How do Scientists test for interspecific competition?

Lab tests, feild studies (one species removed), feild observations (using tests if association between the two species).

Typically if one species is more successful than another in an environment interspecific competition is a reasonable hypothesis.

Whats a hyppothesis

A testable statement on the relationship between two variables.

Can be stested by: Expiriment to test relationship, or repeated observations to determine wether there’s a relationship.

Allelopathy

The release of chemicals from one organisim influencing the growth, germination, reproduction or survival of another organisim.

E.g. Black Walnut tree & Tomatos

How does the Black Walnut Tree utilize Allelopathy?

Black walnut trees produce and release an allelopathic chemical called juglone.

Juglone inhibits the growth of many plants including tomatoes.

Allelopathy reduces competition from other plants for resources needed by the black walnut tree.

How does the Penicillium fungus utilize Allelopathy?

The Penicillium fungus secretes the antibiotic chemical penicillin.

Penicillin inhibits the growth of bacteria near the fungus, reducing competition for resources.

Penicillin is used as a medicine to inhibit bacterial growth.

Top Down Controls

Top down factors are pressures applied at higher trophic levels to control dynamics in an ecosystem.

E.g. The top predator prevents overpopulation of its prey.

Bottom Up Controls

Bottom up factors are resources (such as nutrients) available to producers, affecting the growth of producers.

E.g. Population growth at higher trophic levels is impacted by the availability of producers.

Top down control - Wolves

The Wolves of Yellowstone National Park are a good example of a top-down control.

The Yellowstone ecosystem is more biodiverse due to the presence of wolves.

Bottom-Up of Algal Blooms

Algae are producers. 

Reducing nutrients puts pressure on the lowest trophic level.

Low nutrients results in small populations of algae.

This affects many other species in the ecosystem.

Algal blooms can be controlled by reducing the concentration of nutrients in waterways.

Density dependent control and predator prey relationships + Example

Density dependent factors cause a population's growth to change due to population density. Density dependent factors tend to be biotic.

Predator-prey relationships is an example of a density dependent factor:

The primary food source for  canadian lynxes are snowshoe hares:

1. high hare pop. = more lynx food = high lynx pop.

2. high lynx pop. = more hare predators = lower hare pop.

3. lower hare pop. = lower lynx food = lower lynx pop.

4. lower lynx pop. = less hare predators = higher hare population.