C4.1 Populations and Communities

population

A group of individuals that belong to the same species and live in the same area

reproductive isolation

Separation of species or populations so that they cannot interbreed and produce fertile offspring due geographic, behavioral, or temporal factors, preventing interbreeding between groups.

random sampling

A method of selecting a subset of individuals from a larger population in a way that each individual has an equal chance of being selected.

quadrat sampling

A method used to estimate population size for sessile organisms (e.g., plants, corals) by randomly placing square frames (quadrats) over a habitat and counting the organisms within.

Steps for quadrat sampling

Randomly place quadrats.

Count organisms within each quadrat.

Calculate the mean number of organisms per quadrat.

Extrapolate to estimate population size for the entire area.

Criteria for counting

If an organism touches a quadrat line and more than half is inside, it is counted.

standard deviation

Measures variation in the number of individuals per quadrat. A small standard deviation indicates a consistent distribution, while a large one shows significant variability.

capture-mark-release-capture

Used for motile organisms (e.g., birds, fish) to estimate population size.

steps for capture-mark-release-capture

Capture, mark, and release a sample of individuals.

Recapture a second sample and record the number of marked individuals.

lincoln index

a method for determining population size by marking and recapturing portions of a population

lincoln index formula

Population Size= (M×C)​/R

M = Number marked in the first sample.

C = Total number captured in the second sample.

R = Number of recaptured marked individuals.

carrying capacity

Refers to the maximum population size an environment can support over time, influenced by the availability of resources like food, water, and space. It is dynamic and varies with factors such as resource availability and environmental conditions

Factors affecting carry capacity

resource availability, competition for limited resources, more limiting factors

population density

The number of individuals per unit area or volume. For example, the density of trees in a region or bacteria in a growth medium.

density dependent factors

factor that limits a population more as population density increases. includes competition for resources, predation, disease, parasitism,.

density-independent factors

These factors affect populations regardless of density. Include natural disasters, anthropogenic factors

exponential growth

Occurs in ideal conditions with unlimited resources, represented by a J-shaped curve. This growth is unsustainable in natural ecosystems due to limiting factors like food, competition, and predation.

Sigmoid growth curve

Also known as S-shaped growth, occurs when a population grows in an environment with limited resourcese

ecology

the branch of biology that deals with the relations of organisms to one another and to their physical surroundings.

Intraspecific relationships

interactions that occur between individuals of the same species and are key drivers of population dynamics. can be either competitive or cooperative

competition

Happens when individuals within the same species vie for limited resources such as food, water, space, and mates.

outcomes of competition

adaptation to different ecological niches, population regulation

intraspecific cooperation

occurs when individuals of the same species work together to increase their chances of survival and reproduction. can involve altruistic behaviors

altruistic behaviors

behaviors that come at a cost to the individual doing the behavior for the greater good of their group

communities

complex ecosystems consisting of multiple populations of different species that interact and coexist within a particular area.

roles

The interconnectedness and interdependence of species are vital for understanding the complexity of ecological communities and the importance of biodiversity conservation.

interspecific ecological interactions

between different species within an ecosystem. These interactions influence species distribution, abundance, and evolution

key interactions

include symbiosis, herbivory, predation, competition, and parasitism.

symbiotic relationships

long-term, intimate interactions between different species, often involving mutual dependence. These relationships can result in coevolution and adaptation.

mutualism

a type of symbiotic relationship where both species benefit from the relationship

parasitism

a symbiotic relationship where one species benefits at the expense of the other, often causing harm or dise

herbivory

a relationship where animals, called herbivores, consume plants.

Interspecific competition

occurs when different species compete for the same limited resources, such as food, water, or space. This competition can affect the distribution, abundance, and evolution of species.

pathogens (pathogenicity)

Pathogens are microorganisms (viruses, bacteria, fungi, etc.) that cause disease in their host. Unlike parasites, pathogens often have a more direct and immediate harmful effect.

examples of mutualism

bees and flowering plants, mycorrhizae and orchids, zooxanthellae and corals

invasive species

An organism that is not indigenous, or native, to a particular area and can potentially cause harm to the ecosystem

endemic species

Refers to a species that is naturally found in a specific geographical region and is not found naturally elsewhere.

chi-squared test

helps determine if there is a significant association between two categorical variables. In community ecology, this is used to assess if two species are associated (either positively or negatively).

categorical variables

Variable in statistics that represents a distinct category from a fixed group.

Null Hypothesis (H₀)

There is no significant association between species X and Y.

Alternative Hypothesis (Hₐ):

There is a significant association between species X and Y.

contingency table

A table showing the observed frequencies of species X and Y in different quadrats. This table shows the presence or absence of both species in different quadrats.

population control

Refers to the regulation of population sizes to maintain ecological balance and prevent overexploitation of resources.

predator-prey relationships

Predators help regulate prey populations through selective pressure, leading to a dynamic cycle of population growth and decline.

Top-Down Control

occurs when organisms at higher trophic levels (predators) influence the abundance of species at lower trophic levels (prey).

Bottom-Up control

occurs when resources at lower trophic levels (e.g., plants, nutrients) influence the abundance of species at higher trophic levels (e.g., herbivores, predators).

allelopathy

This is the release of chemical substances by plants to inhibit the growth of nearby competitors.

antibiotic secretion

Certain microorganisms release antibiotics to inhibit the growth of competing species.