unit 3.4-3.5 - carrying capacity, population growth, resource availability

individual

living organism

population

individuals that belong to same species and live in given area at particular time

community

all populations of organisms within given area

ecosystem

particular location on earth with interacting biotic/abiotic factors

biome

set of ecosystems sharing similar characterisitcs

biosphere

region of our planet where life resides

population ecology

study of factors that cause populations to increase or decrease

population dynamics

how the number of individuals in population change over time

5 characteristics of population

1. size

2. density

3. distribution

4. age structure

5. population sex ratio

conservation efforts/pest control

why is it important to understand factors that influence population size

population size

total number of individuals within defined area at given time

population density

number of individuals per unit area at a given time

helps determine if species are rare or abundant

density-dependent factors

factors that influence individuals probability of survival and reproduction → DEPENDS ON POPULATION SIZE

ex. competition, predation, disease, food availability, territory size

density independent factors

factors that have same effect on individuals probability of survival/reproduction at any population size

ex. natural disasters(storms/fires), heat waves, droughts, pollution/poison, human disturbances

density-dependent factors intensify effect on organism as population numbers increase, density-independent don’t

how do density independent/density dependent factors influence population size

population distribution

description of how individuals are distributed within respect to each other

3 patterns of distribution - random, uniform, clumped

random distribution

typical of species in which organisms do not interact strongly

ex. spiders, seed dispersal

uniform distribution

common among territorial animals/plants that produce toxic chemical to prevent other plants of same species from growing close to them

also typical of species that compete for a scarce environmental resource

ex. territorial animals, creosote bush

clumped distribution

provides enhanced feeding opportunity, protection from predators and care for young

may reflect a patchy distribution of resources in an environment

ex. herding animals

age structure

description of how many individuals fit into particular age categories in population

helps predict how rapidly a population can grow

sex ratio

ratio of males to females in population

sex ratio is around 50:50 in most sexually reproducing species

population growth models

mathematical equations that can be used to predict population size at any moment in time

1. exponential growth model

2. logistic growth model

population growth rate

number of offspring an individual can produce in given time period, minus deaths of individual/offspring in same period

exponential growth

under ideal conditions the probability of an individual surviving increases

high #births low#deaths = high population growth rate → exponential growth

exponential growth model

N_t=N₀e^rt

estimates population’s growth size (N_t) after period of time (t) based on intrinsic growth rate r and number of reproducing individuals currently in population N₀

describes continuously increasing population that grows at fixed rate

intrinsic growth rate

r - maximum potential for growth of population under ideal conditions with unlimited resources

when conditions are less favorable, population growth rate is lower than intrinsic growth rate bc individuals produce less offspring and deaths increase

biotic potential

another name for intrinsic growth rate

exponential growth model

allows us to estimate future population N_t=N₀e^rt

N_t= future size of population

t= amount of time over which population grows

r=intrinsic growth rate of population

N₀=current size of population

e=base of natural logarithm (2.72)

J-shaped curve

curve of exponential growth when graphed

population not limited by resources → growth = very rapid, more births with increased reproducing individuals over time = J shaped curve

finite

total resources in ecosystem are _____

due to environmental limits (limiting resources) populations do not expereince exponential growth indefinitely, so population growth is limited by resource availability and space

limiting resource

resource that population cannot live without and occurs in quantities lower than the population would require to increase in size

logistic growth model

growth model that describes population whose growth is initially exponential, but slows as the population approaches carrying capacity K of environment

more realistic because it incorporates environmental limits

carrying capacity (K)

limit of how many individuals in population the environment can sustain

S-shaped curve

shape of logistic growth model when graphed

initially exponential growth, as pop grows larger, less resources, growth rate slows, stops at carrying capacity → s-shaped curve

density-dependent factors

which factors are accounted for when using logistic growth model to determine carrying capacity of population - density-dependent or density-independent (unpredictable)

overshoot

population becomes larger than environments carrying capacity

leads to resource depletion

die-off/die-back

rapid decline in population due to death

major ecological impact of population overshoot

lack of available resources like food/space lead to disease, famine and/or conflict

oscillate

most populations experience cycles of overshoots/die-offs that _______ around the carrying capacity

environmental resistance

population encounters resistance to exponential growth as it begins to fill up enviroment

equilibrium level

population fluctuates around this area

caused by variations in birth rate and death rate as a result of population density exceeding of falling below carrying capacity