Interdependence between species

What is a species?

A group of organisms that can potentially interbreed to produce fertile, viable offspring.

What is a population?

A group of organisms of the same species, living in the same area at the same time.

What is a community?

A group of populations living together and interacting with each other within a given area.

What is a habitat?

The environment in which a species normally lives, or the location of a living organism.

What is an ecosystem?

A community and its abiotic environment (i.e. habitat).

• Population + habitat.

What is ecology?

The study of the relationship between living organisms, or between living organisms and their environment.

What is population structure?

The variety of genotypes and phenotypes within a population.

• Helps scientists determine how populations change over time and predict future changes.

• Based on 3 factors: Size, density and distribution

What are the factors considered for population structure?

1. Size.

2. Density.

3. Distribution.

What is population size?

The number of individual organisms of the same species, living in the same area at the same time.

• Small populations are more vulnerable if the environment changes, due to a smaller gene pool (less genetic variation).

What is population density, and how does it relate to carrying capacity?

Population density: The average number of individuals in a population per unit area or volume

Carrying capacity: The total population that can be supported by an environment

• As population density approaches carrying capacity, resources (food, water, shelter) become more limited relative to demand

• If population density exceeds carrying capacity, competition for resources increases

• This can can lower survival and reproduction rates until the population decreases to within the carrying capacity

What is population distribution?

Describes how individuals are spread across a specific area

What are interspecific relationships? How are they classified?

Interspecific relationships: Relationships between species

• Classified according to whether they help, harm, or have no effect on the species involved

What are the main types of interspecific relationships?

1. Competition.

2. Predation.

3. Herbivory.

4. Symbiosis (4 types).

What is interspecies competition?

Interaction that occurs when individuals of different species compete for a resource that limits their growth and survival (e.g. food, water, shelter)

• Can be described as amensalism

• A driver for evolution, as advantageous traits can increase success in competition, leading to adaptations in the population.

What is predation? What are some adaptations of each in the relationship?

An interaction between species in which one species (the predator) kills and eats the other (the prey)

• Predator adaptations: Acute senses to enable them to locate + identify potential prey, and structural adaptations including claws, teeth, fangs, stingers or poison to catch and subdue prey

• Prey adaptations: Eyes on the side of the head, playing dead, more herding and socialisation, distinct feeding times to avoid predation

What does the predator-prey relationship describe?

• Because the predator relies on the prey as a food source, their population levels are inextricably intertwined

• If the prey population drops (e.g. due to over-feeding), predator numbers will decrease as intraspecific competition increases

• If the prey population rises, predator numbers will increase due to the over-abundance of a food source.

What is herbivory? How do plants defend themselves against it?

An interaction where an organism eats part of a plant or algae

• Unlike prey animals, plants cannot run away to avoid being eaten

• Instead, plant defences against herbivores include chemical toxins or structures (e.g. spines and thorns)

• Most herbivores are invertebrates such as grasshoppers and beetles.

What are examples of herbivory on land and in aquatic environments?

Land examples: mammals and birds eating grasses and leaves.

Aquatic examples: snails, urchins, and some fish and mammals.

What is symbiosis?

A close and long-term interaction between two different species living together

What are the types of symbiotic relationships?

1. Parasitism.

2. Mutualism.

3. Commensalism.

4. Amensalism.

What is parasitism? How does it affect the population structure of their host?

A symbiotic interaction in which one organism (the parasite) gets its nutrition from another organism (its host), which is harmed in the process.

• Parasites can change how a host acts to help themselves move to a new host.

• They can significantly affect the population structure of their host population by affecting survival, reproduction and population density.

What is an example of parasitism?

• Ticks (ectoparasites) live on moose, weakening the host by withdrawing blood and causing hair breakage and loss.

• This increases the chances of the moose dying from cold stress or predation by wolves.

What are the types of parasites?

Endoparasites: exist inside a host's body.

• Examples: tapeworm, roundworm, flatworms.

Ectoparasites: exist outside a host's body.

• Examples: ticks, lice, fleas, mites, mosquitoes.

What is mutualism and what are some examples?

A symbiotic relationship where both species benefit.

Examples: Clown fish + sea anemone, bees and flowers (cross-pollination), fruiting trees and animals (seed dispersal), algae and coral (algae get shelter, coral get food).

What is commensalism? How often and how do they occur in nature?

A symbiotic relationship where one species benefits but doesn't harm or help the other

• Commensal interactions are rare in nature, because any close interaction between species likely affects both species, even if only slightly.

• Some possibly commensal associations involve one species obtaining food that is inadvertently exposed by another.

What are examples of commensalism?

Herbivores tilling land: Exposes insects in the soil for other mammals but doesn't affect the herbivores.

Barnacles on whales: Barnacles get a safe habitat and access to food sources, while the whale is generally unaffected.

What is amensalism?

A symbiotic relationship where one species is harmed and the other is unaffected (neither helped nor harmed).

• Occurs in the form of competition or antibiosis.

How to remember: think "anti-biology" - goes against living things.

What are the types of amensalism?

1. Competition.

2. Antibiosis.

What is competition, as a type of amensalism?

One organism is harmed because a larger or more powerful organism excludes it from a resource (food or shelter), while the larger organism is unaffected.

Example: Large trees shading out and stunting the growth of smaller plants beneath them

What is antibiosis?

One organism releases a chemical that harms another organism, without being affected itself

Example: Penicillium releases penicillin, which kills nearby bacteria.