Chapter 20: Population Growth and Interactions

Community

A group of associated populations of more than one species within a define area.

Population Density (Dp)

Define as the number of individual organisms (N) in a given area (A) or volume (V). Dp = N/A or Dp = N/V

Population Distribution

Patterns of distribution of a population in a given area, can be clumped, random, or uniform.

Population Explosion

A sudden increase or burst in the population in either a certain geographical area or worldwide.

Population Crash

A dramatic decline in the size of a population over a short period of time.

Clumped Distribution

Individuals are grouped in patches where resources like food, water, or shelter are abundant. Common in nature—seen in humans, aspens, and Banff springs snails.

Random Distribution

Individuals are spread unpredictably, with no set pattern. Occurs when resources are abundant and competition is low. Rare in nature—may be seen in moose during summer.

Uniform Distribution

Individuals are evenly spaced, often due to territorial behavior or human management. Seen in birds of prey, like golden eagles, and agricultural fields.

Changes in Population Size

Depends on how fast population growth/shrinks.

- Increase = birth rate/natality (n) and immigration (i).

- Decrease = death rate/mortality (m) and emigration (e).

Immigration and emigration only occur in open populations.

ΔN = (n+i) - (m+e)

Growth Rate

The change in the number of individuals in a population (ΔN) over a specific time frame (Δt).

gr = ΔN/Δt

Per Capita Growth Rate

The change in population size expressed as the rate of change per individual. Determined by calculating change of individual (ΔN) relative to N.

Cgr = ΔN/N or Cgr = (Nfinal-N)/N

Biotic Potential

The highest possible per capita growth rate for a population. Dependent on the number of reproductive cycles, number of surviving offspring, age of reproductive maturity, number of times of reproduction, and life span.

Exponential Growth Pattern

A brief lag phase, followed by a steep increase in growth curve. Described as J shaped. The pattern of population growth that results from unlimited resources. Population size increases by a fixed rate, variable "r" indicates rate of exponential growth.

Lag Phase

In the beginning of population growth, where the growth of a small population is slows since there are only a few individuals to reproduce.

Stationary Phase

When the birth and death rates of a population are equal due to lack of food limiting energy available for reproduction.

Logistic Growth Pattern

An S-shaped (sigmoidal) curve representing a habitat's carrying capacity.

Log Phase

Also known as the growth phase, dependent on biotic potential of organisms.

Carrying Capacity

The theoretical maximum population size that the environment can sustain over time -> represents the number of individuals in a population that can live in a given environment without depleting needed resources or harming the habitat. Over time, population changes around carrying capacity in stable equilibrium (k).

Density Dependent Factors

Biotic factors that limit a habitat's carrying capacity. The impact of density-dependent factors increases with population density. Competition, disease, and predation.

Density Independent Factors

Abiotic factors limiting a habitat's carrying capacity through harsh weather, droughts, floods, forest fires, etc. This limits growth regardless of size or density.

Environmental Resistance

Any factor that prevents a species from reaching its carrying capacity. Both abiotic and biotic factors.

R-Selected Strategies

Species that have a short lifespan and an early reproductive age, and they produce large broods of offspring with little to no parental care. They are adapted to increase population. Density independent mortality. Small body, reproduce quickly, exponential growth.

K-Selected Strategies

Populations that live close to the carrying capacity of their habitats (k-selected strategies). Density dependent mortality. Long lifespan, late reproductive age, large body size, small number of offspring (logistic growth), reproduce less often, and long gestation periods.

Ecological Community

An association of interacting populations that inhabit a defined area.

Intraspecific Competition

The competition for limited resources among members of the same species. A density-dependent factor that limits population growth. Plays a role in natural selection. (Individuals that have a competitive advantage are more likely to survive).

Predation

An interaction in which one organism kills another for food.

Increased when prey experience higher competition for food resources leading to decreased food availability and poor health.

Interspecific Competition

Competition between two or more populations for limited resources, such as nutrients, light, or living space. (No two species can share the exact same ecological niche).

Predators

Organisms that kill and consume other organisms known as prey.

Interference Competition

Fighting for resources.

Exploitative Competition

Consumption of shared resources. Eg. woodpecker destroys nests of wren.

Cryptic Colouration

It's camouflage that helps prey blend into their surroundings to avoid detection by predators.

Warning Colouration

Bright colors like black, yellow, and red warn predators that an animal may be harmful or unpalatable.

Batesian Mimicry

When a harmless species mimics a harmful one to deter predators (e.g., syrphid fly mimics yellowjacket wasp).

Mullerian Mimicry

When two harmful species mimic each other for mutual benefit (e.g., monarch and viceroy butterflies).

Niches

The habitat and particular role an organism plays in the environment

Symbiosis

The direct or close relationship between individuals of different species that live together.

Mutualism

When both partners in a symbiotic relationship benefit from the relationship in order to survive. Eg. lichen is combination of alga and fungus allowing growth on bare rock. Alga performs photosynthesis and fungus protects drying of alga and produces acid that dissolves rock.

Commensalism

A symbiotic relationship in which one partner benefits and the other partner neither benefits nor is harmed such as a shark and a suckerfish.

Parasitism

A form of symbiosis in which one partner, the parasite benefits at the expense of the host, Eg. Viruses.

Succession

The sequence of invasion and replacement of a species over time. Driver by both abiotic factors, such as climate, and biotic factors, such as interspecific competition for changing avaiable resources.

Primary Succession

Begins when there is no soil present, such as on bare rocks left behind by a retreating glacier or on a hardened lava bed. According to the classical mode of succession, species populate an area in a specific chronological order.

Pioneer Community

The first species to colonize an area and initiate succession. Usually lichens, which grow in harsh conditions, change the pH of soil after soil buildup. Allows other species to grow.

Climax Community

The late comers in succession. This community remains relatively stable if there are no major environmental changes.

Ecological Disturbance

An event that changes the structure of a community sometimes destroying all actively growing organisms.

Secondary Succession

The recolonization of an area after an ecological disturbance, such as a forest fire or flood or agricultural activity (the soil is usually not destroyed and seeds remain). Includes changes in the number of species over time.

Genetic Changes

Alterations in the genetic material that are passed from one generation to the next, affecting future populations and influencing evolutionary processes.

Ecological Communities

Groups of interacting organisms sharing a common environment, which are in constant flux, with organisms and the non-living environment changing in response to each other.

Sustainability Concept

The principle of meeting current human needs without compromising the ability of future generations or the health of the planet to meet their own needs, integrating social, economic, and environmental factors.

Age Pyramids

Graphical tools used by demographers to assess a population's potential for growth by displaying the percentage of males and females in different age categories.

Reproductive Stage

The age group within a population comprising individuals from 14 to 44 years old, primarily responsible for the current birth rate.

Post-Reproductive Stage

The age group within a population comprising individuals 45 years and older, who are typically past their reproductive years.

Pre-Reproductive Stage

The age group within a population comprising individuals from 0 to 14 years old, representing the potential for future births.

Explosive Growth

In humans, primarily driven by Agricultural Revolution: Invention and agriculture (10,000 years ago)

Industrial Revolution: better machines for food production (19th century) and improved transportation systems (move food more efficiently)

Medicine science, water purification/sewage treatment: reduction in infant mortality and increased survivorship to reproductive age