Interdependencies between species

The population size of a species is a simple count of the total number of members within any given population.
Over time population sizes can increase or decrease, components that can alter its size are total births and deaths within a population and immigration and or migration between populations.
Carrying Capacity is the limit of individuals an environment can support and sustain indefinitely.
Many biotic and abiotic factors of an ecosystem can also influence the births, deaths, immigration and emigration observed in a population and therefore the overall population size.
Population distribution of a species refers to the geographical spread across different areas, this distribution is limited by the ideal habitat of a species and its ability to tolerate different environments.
Population growth can be affected by temperature, rainfall, invasive species, and habitat loss.
Population density of a species refers to the number of individuals found in a specific area such as individuals per square kilometre. It’s useful when predicting population growth rates and carrying capacity for a particular species.
Dense populations tend to see up available resources in an ecosystem more quickly than a less dense population.
Density-independent factors are environmental factors that affect population growth but are not affected by population density.
Density-dependant factors are environmental factors that affect population growth and become stronger as population density increases.
Examples of density-independent factors are; climate, natural disturbance events, and functionally unlimited resources.
Examples of density-dependant factors are; disease, predation, competition, resource availability, and accumulation of waste.
When density is low, density-dependant factors will have almost no influence on population growth
When density increases the effect of density-dependant factors becomes more severe, the population growth rate will begin to slow until the population size remains constant.

Interactions between species:

Interactions between species are called by many species sharing habitats and interacting with each other.
Symbiosis is the interaction of two species living in close proximity to each other.
The types of symbiotic interactions are; Mutualism, commensalism, amensalism, parasitism, predation, and competitors.
Parasitism (+/-) is an interaction where one organism obtains nutrients at the expense of another organism.
Mutualism (+/+) is an interaction where both organisms benefit.
Amensalism (0/-) is an interaction where one organism experiences some negative effects while the other organism is unaffected.
Commensalism (+/0) is an interaction where one organism benefits and the other is not seriously harmed.
Predation (+/-) Is an interaction where one organism hunts and kills the other organism for food.

Competitors (-/-) Is an interaction between two organisms of either same or different species competing for food.

Keystone species:

Keystone species are species within any given ecosystem that play a disproportionally large role in maintaining the structure of the ecosystem, they tend to have a large effect on the ecosystem when removed. They are crucial for ecosystem functioning.
Keystone species tend to adopt similar roles in the ecosystem, either apex predators or ecosystem engineers.
Apex predators have no natural predators and are at the top of its food chain. They are responsible for controlling the numbers of their prey, and subsequently the number of many other organisms within an ecosystem.
Ecosystem engineers are organisms that significantly alter, create, or maintain the structure of an environment.
Interspecific competition is competition for resources between members of different species
Intraspecific competition is competition for resources between members of the same species.