enviro exam chapter - 3

Ecology

Study of interactions among organisms and of the relationships between organisms and their environment (may be done at any level)

Organism

An induvidual

Population

A group of individuals of a species that live in a particular area

Community

a set of populations interacting in an area

Ecosystem

The abiotic and biotic components of an area

Biosphere

The total of living things on Earth and areas they inhabit

Habitat

Specific environment in which an organism lives, including biotic and abiotic components. (Organisms have specific habitat requirements-tolerance limits. Survival depends on the availability of suitable habitat.)

Niche

Functional role of a species in a community “job”. Use of habitat, resources, role in flow of energy, interactions with other species

Specialists

Organisms with narrow niche requirements (panda- needs specific habitat and eats mostly bamboo. without either of those it struggles to survive)

Generalists

Organisms with broad niche requirements (raccoon- can live in forests, cities, and suburbs. Eats fruits, insects, small animals, and human food. Can adapt to different conditions)

Population ecology

Factors that regulate population abundance and distribution (Population ecology is the study of how populations of organisms change in size, density, and distribution over time. It examines factors like birth rates, death rates, immigration, emigration, and how the environment affects populations)

Population size

The # of individuals present at a given time. Below the minimum number of individuals (minimum viable population), a species may not be viable in the long term.

Ex: California condor population size was reduced to 22 in 1987. Captive breeding programs have led to its recovery.

Ex: The American passenger pigeon was probably the world’s most abundant bird 200 years ago; population est 3-5 billion (Overhunting and habitat destruction caused its extinction)

Population Density

Number of individuals/unit area at a given time (successful population density varies by species)

Low density

Individuals may be unable to find mates, or may only find closely related ones. Courtship rituals, flocking, schooling, foraging, and genetic variability often depend on population density

High density

Competition for space, food, and mates, and the spread of infectious disease increased.

• Passenger pigeons required large flocks to initiate courtship and avoid predation. When reduced to small groups, the species couldn’t survive

• Chronic wasting disease - spread linked to overpopulation of deer, moose, and elk

Population distribution

How individuals are distributed with respect to one another

Random

Individuals located in no particular pattern, occurs when resources are plentiful and there is little competition

Uniform

Individuals are evenly spaced when there is no competition for space

Clumped

Individuals seek resources that are unevenly spaced - food, water, and shelter

Population sex ratio

Proportion of males to females in a population

• Monogamous species = 1:1 ratio of males to females for maximum population growth

• Polygynous species = Sex ratio can be skewed towards females and still have maximum population growth

Population age structure

Relative # of individuals of different ages within a population

• Together with the reproductive potential of each individual in each age class, predictions can be made about whether populations will increase or decrease

• Ex: only 1 known 90-year-old female of the Yangtze soft-shell river turtle. Only 3 known males left; 5 breeding attempts failed; she died in April of 2019.

r-selected species

The population of a species grows quickly as resources become available, often followed by overshoots and die-offs. High rate of population increase, well adapted to exploit unpredictable environments. “r” denotes the intrinsic growth rate.

Characteristics:

• short life

• rapid growth of individual

• early maturity

• many small offspring

• little parental care

• adapted to unstable environment

• prey

• niche generalists

“K” selected species

Species that grows slowly until it reaches carrying capacity. Abundance is determined by carrying capacity -”K "). Ex: elephants, whales, humans. Low reproductive rates; very responsive to environmental conditions. Decrease or increase slowly as resource availability changes.

Characteristics

• long life

• slower growth of individual

• late maturity

• few, large offspring

• high parental care

• adapted to stable environment

• predators

• niche specialists

Survivorship Curves: Type I

Excellent survivorship over lifespan

Survivorship Curves: Type II

Relative constant decline

Survivorship Curves: Type III

Low rates of early survivorship

Population growth models

Equations used to predict population size at any moment in time

Growth rate

The # of offspring an individual can produce within a given time period, minus the deaths of the individual or offspring during the same period

Intrinsic growth rate

Under ideal conditions, with limited resources, the max potential for growth (denoted as “r”0 for population

Population change is determined by 4 factors: 1. Natality

Births within a population

Population change is determined by 4 factors: 2. Mortality

Deaths within a population

Population change is determined by 4 factors: 3. Immigration

Arrival of new individuals from outside of the population

Population change is determined by 4 factors: 4. Emigration

Departure of individuals from the population

Exponential growth model

Describes a population that grows continuously and at a fixed rate.

• if population is not limited by resources, growth can be very rapid due to many births, forming a j-shaped curve when population size is graphed against time

Exponential growth model - J-shaped curve growth

Normally occurs in nature when a population is small, competition is minimal, removal or absence of predators, and environmental conditions

Logistic Growth Model

Population whose growth is initially exponential, but slows as population approaches the carrying capacity.

Logistic Growth Model - S-shaped curve

The Logistic Growth Model is an S-shaped curve that shows a population growing quickly at first, then slowing down as it reaches its carrying capacity. It happens because resources like food, water, and space become limited, causing the population to level off.

Remember: S-shaped = starts slow, grows fast, then levels off.

Logistic Growth Model - Carrying capacity (K)

Limit of how large a population can be sustained by limiting factors - physical, chemical, and biological attributes of the environment that restrain population growth

Variations on logistic model-overshoots and crashes - K-selected species

They tend to be stable in undisturbed areas - slow increases and decreases in response to the environment

Variations on logistic model-overshoots and crashes - r-selected species

Sometimes populations have sudden growth with high peaks, may overshoot carrying capacity, drop below it, and increase and overshoot it again until they settle close to carrying capacity. Some populations will continue to overshoot and crash

Factors that Influence Population

Density-dependent factors:

Limiting resources influence an individual’s probability of survival and reproduction

Effects of density-dependent factors increases as populations grow

• For terrestrial plants: water + soil nutrients

• For animals: food, water, and nesting site resources

• Resistance factors: also control population size and growth

• Disease, competition, predation

Density-independent factors

Have the same effect on an individual's likelihood of survival and reproduction, at any population size

Includes:

• hurricanes, tornadoes, floods, fires, volcanic eruptions, environmental temperatures, etc

Carrying capacities can change

Alteration of natural environments due to habitat loss, resource extraction, and population pressure has altered the carrying capacities of environments. Conservation of threatened species by protecting habitats may not be effective in the future with global climate change

Ex: The changing distribution of forest habitats and rainfall patterns in Hawaii are

causing declines in some species of honeycreepers