A scientist studies how the number of coyotes in San Diego County has changed over the last decade. Is this a population-level study, a community-level study, or an ecosystem-level study?

Populations are groups of individuals from the same species, with similar characteristics, capable of crossing, leaving offspring, and living in the same habitat at the same time. These groups are reproductively isolated from other species groups. Individuals belonging to a species cannot reproduce with members of other species.

What results of interest about this organization level is knowing the minimum size of the population needed to leave fertile offspring that ensure the population will survive over time. Genetic variability is also a significant factor because it allows evolutive adaptation to environmental changes. A population might be severely affected by evolutive forces such as genetic flow, genetic drift, and natural selection.

When analyzing the evolution of a population in time, there are parameters to consider regarding its size, such as the generational time, growth rate per capita, the net reproductive rate, the reproductive value, among others.

A community might be defined as a group of organisms of different species that coexist in a specific time and space.

When ecologists talk about a Community, they refer to the existing interaction between different species that share the same habitat and at the same time. What results of interest about the study of this organization level are the inter-specific interactions. These interactions involve competition, predation, parasitism, mutualism, etcetera, and each species carries out a different role in these interactions. These relationships and the results are what determine the destiny of the populations and their size.

The ecosystem is composed of living and non-living things that interact and depend on each other. These are the biotic and abiotic factors.

• Abiotic factors are physical and chemical components of the ecosystem. These are the non-living elements.

• Biotic factors are all the living components in the ecosystem.

Biotic and abiotic factors influence the survival and reproduction of living beings. These are constantly interacting. If one of these components is removed, the whole ecosystem will change because its equilibrium has been altered.

Every abiotic component influence organisms and their survival and reproductive rates.

When analyzing how the number of coyotes in San Diego County has changed over the last decade, we are performing a population-level study. We need to know how the population changed its size through the years, but not the interactions with other species or abiotic factors. Interactions are not of interest in this study.