module 9 Flashcards
Population growth describes
Describes how the number of individuals in a population changes over time
Individuals
added through leave through
Added through births and immigration
Leave through deaths and emigration
Populations may be:
open closed populations
Open population Has immigration and emigration Closed population Does not have or has a very low level of immigration & emigration Doesn’t influence population growth
Age Structure
Relative Proportion of a population in different Age Classes
Required to Understand Growth & Regulation
Age-Related Birth Rates
Potential Mortality
Age-Specific Rates
Birth and Death Rates vary with age
as age increases birth rates and death rtes
Birth and Death Rates vary with age
as age increases birth rates decrease death rates increase
Life Tables
cohort
Cohort or Dynamic
Follows a group of individuals throughout their lifetimes
Plants, Sessile Animals, Isolated Regions
Difficult to accomplish
Time consuming
Table may not relate to future generations
Maintain individual Records
Static (Time-Specific) Life Table
Age-specific survival & fecundity of individuals of different ages within a population at a given Time
Limited by ability to Age Individuals
Assume:
Cohort Sizes Constant
Newborn Populations of each age Class
Environmental Factors similar among all cohorts
Follow Individuals for short period
Best mortality rates
Age At Death
Age Structure at specific time
x
– age or age class
ax (nx)
Number alive at beginning of age class
lx –
Survivorship
Proportion of all individuals surviving to beginning of age class
dx –
Death Rate
Proportion of all individuals dying in age class
mx –
Mortality Rate Proportion of individuals that are alive at beginning of age class and that die during age class
sx –
Survival Rate Proportion of individuals that are alive at beginning of age class and that die during age class
ex –
Expectation of future life Average time span that an average individual in age class has left before death
bx (mx) –
fecundity rate Average number of offspring/seeds produced May be #/-individual or #/-female # of female offspring / adult female Polygynous or Promiscuius Sexually Dimorphic # of offspring / individual Monogomous
Type I
Majority of mortality occurs among older individuals.
Dall Sheep
Type II
Constant rate of survival throughout lifetime.
American Robins
Type III
High mortality among young, followed by high survivorship.
Sea Turtles
Birth Rate
Number of young born per female.
Crude birthrate
Number of birth during some time period (usually a year) divided by estimated population size at the beginning of the time period, multiplied by 1000
Fecundity Schedule
Tabulation of birth rates for females of different ages.
Age-specific birthrate (bx)
Sexually Dimorphic Species
Mean number of females born to each female in an age group
Female is reproductive Unit
Population increase as a function of number of females
Species with Similar Sexes
Mean number of offspring born to each individual in an age group
gross reproductive rate
Sum (Σ) across all age classes
Ro
= Net Reproductive rate
Average number of seeds/offspring produced by an individual in a population during its lifetime.
Ro=Σ lx bx
If R0 = 1.0
Population is stable
Females on average produce one daughter, replacing themselves
If R0 > 1.0
Population is growing
Females on average produce more than one daughter;
If R0 < 1.0
Population is declining
Females on average produce less than one daughter;
Stable Age Distribution
if the population is growing or declining, all age classes grow or decline at the same rate
Proportion of each age class the same in the population Population growth becomes more predictable
Geometric Rate of Increase (Finite multiplication rate) (λ):
λ = R0 when generations
λ = R0 when generations do not overlap
λ = N t+1 / Nt
N t+1 = Size of population at future time.
Nt = Size of population at some earlier time.
Generations Overlap
Population growth rate not equal to what
Population Growth Rate ≠ R0
Growth Rate =
(B – D) + (I – E)
Geometric Growth appropriate for \_\_\_\_\_ growth \_\_\_\_\_\_\_ generations \_\_\_\_\_\_\_ growth what symbol
Appropriate for: Discrete growth Non-overlapping generations Unlimited growth Nt = N0λt lambda
Exponential Growth Appropriate for populations: Growing \_\_\_\_\_\_ \_\_\_\_\_\_ generations what symbol?
Appropriate for populations: Growing continuously With overlapping generations. Unlimited Environment Nt = Noer0t r
On average, small organisms have:
Higher rates of per capita increase
Logistic Growth what symbol \_\_\_\_ shaped curve as resources are depleted population growth
Logistic population growth. r0 Sigmoid (S-shaped) population growth curve. As resources are depleted Population growth rate slows Eventually stops dN/dt = r0N(1-N/K)
Carrying capacity (K)
Number of individuals of a population the environment can support.
Finite amount of resources can only support a finite number of individuals.
r0 (rmax
only occurs when Thera are no
intrinsic rate of increase
Maximal per capita rate of increase possible in a population
Biotic potential
Rarely achieved in nature
Only occurs when no limits to growth exist
r
in exponential growth r=
instantaneous growth rate Per capita rate of increase at any time Varies based on conditions Exponential rate of increase In exponential growth: r = r0
Populations
increase
decrease
maximal growth at
Increase below K
Decrease above K
Maximal Growth at K / 2
Equillibrium Occur when:
b = d
Density-dependent factors
Disease, Resource competition, predation
Most important in:
Large animals
Constant environments
Density-independent factors
Natural disasters, Environmental Conditions
Regulation
Control of Population size with relation to Population Size
Density-Dependent
Intensity influenced by Density of Organisms
Limitation
Control of Population Size with no relation to Population Size
Density-Independent
Competition
Individuals use a common resource that is limited
Not enough for all individuals who need it
No competition when:
Availability of resource is sufficient for all AND
Does not affect survival, growth, and reproduction
Intraspecific competition
Competition among individuals of the same species
Members of same species usually have very similar requirements
Scramble competition
Resources equally available to all
All individuals suffer
May lead to extinction or extripation
Contest competition
Some claim enough resources for themselves
while denying others a share of those resources
Exploitation competition
Result of ____ interactions
Result of indirect interactions
Individuals use resources
Reduces amount available for others
Interference competition
Result of direct interactions
Individuals use resources and prevent others from accessing resources
As population density increases,
Space available for each individual becomes
Increased _______ interactions
may cause ______
Space available for each individual becomes restricted
Increased Aggressive or antagonistic interactions
May cause stress
Stress can
Trigger hormonal changes suppress growth curtail reproduction delay sexual activity Suppress the immune system If a pregnant female increase fetal mortality lead to reduced milk production or lactation Stunting the growth and development of nursing young
Dispersal Can Be Density Dependent
Some animals disperse Leaving the population to find a new habitat Dispersing Individuals May: Die before finding suitable habitat Find habitat Not connected to population (Emigration) Considered a decrease to populations May find marginal habitat Lower resource availability Decreased reproduction and Increased Mortality
Home range
Area that an animal normally uses over the course of a year Home Range size availability of food mode of gathering food body size metabolic needs Not defended or exclusive to one individual
Territory
Part of the home range that an animal defends
For its exclusive use of resources
Usually smaller than home range
If an animal defends its entire home range, they are the same
Behavioral defenses of a territory include:
songs and calls intimidation displays Birds spread their wings and tails Mammals bare their teeth attacking and chasing intruders scent marking to deter intruders Territories of different individuals within a population are usually regularly distributed
Space limitation
Number of territorial owners a habitat can support
Resource Limits from decreased Territory Size
Increases in density smaller territory size less resources in Territory
Energy Costs to defend Territory
More Challenges to territory
Allee effect
Density-dependent mechanisms that reduce birthrate and survival when a population is at low density Difficulty in finding mate pheromones carry a limited distance Pollination Social Breakdown Leks Pack Hunting
Density independent factors include:
temperature precipitation severe storms fires floods drought These influence birth- and death rates but do not regulate population growth
When environment conditions exceed the zone of tolerance for an organism it can affect
growth age of maturity reproduction survival movement If conditions are extreme Population can go extinct
