POPULATIONS & CARRYING CAPACITY 02 June 2010 Populations.ppt

Population: all the individuals of a species that live together in an area Demography: the statistical study of populations, make predictions about how a population will change 02 June 2010 Populations.ppt

Three Key Characteristics of Populations Size, number of individuals (N) Density (N/ area) Dispersion, Random, uniform, clumped, (appropriate scale) 02 June 2010 Populations.ppt

Three Key Characteristics of Populations 1. Size: number of individuals in an area Characterized by (N) Growth Rate: Birth Rate (natality) - Death Rate (mortality) (How many individuals are born vs. how many die) 02 June 2010 Populations.ppt

Three Key Characteristics of Populations 2. Density: measurement of population per unit area or unit volume Pop. Density = # of individuals ÷ unit of space 02 June 2010 Populations.ppt

4 Factors that affect density 1. Immigration- movement of individuals into a population 2. Emigration- movement of individuals out of a population 02 June 2010 Populations.ppt

4 Factors that affect density 3. Density-dependent factors- Biotic factors in the environment that have an increasing effect as population size increases   Ex. disease competition parasites 4. Density-independent factors- Abiotic factors in the environment that affect populations regardless of their density   Ex. temperature storms habitat destruction drought 02 June 2010 Populations.ppt

Three Key Characteristics of Populations Dispersion: describes their spacing relative to each other 02 June 2010 Populations.ppt

Dynamic characteristics of populations Age distribution, proportions of young, middle-aged, old Differs in growing, stable, decreasing populations 02 June 2010 Populations.ppt

Factors That Affect Future Population Growth Immigration + + - Population Mortality Natality - Emigration

Changes in populations Growth Expansion of species’ populations may lead to evolution of new species Decline Shrinking species’ populations may lead to extinction Small populations Narrowly specialized species 02 June 2010 Populations.ppt

Changes in populations ΔN = +B +I –D –E +B = births (birth rate) +I = immigrants (immigration rate) – D = deaths (death rate) – E = emigrants (emigration rate) (For many [most] natural populations I and E are minimal.) 02 June 2010 Populations.ppt

Other factors that affect population growth Limiting factor- any biotic or abiotic factor that restricts the existence of organisms in a specific environment. EX.- Amount of water Amount of food Temperature 02 June 2010 Populations.ppt

Other factors that affect population growth Carrying Capacity- the maximum population size that can be supported by the available resources There can only be as many organisms as the environmental resources can support 02 June 2010 Populations.ppt

J-shaped curve (exponential growth) Carrying Capacity Nu m b e r J-shaped curve (exponential growth) Carrying Capacity (k) S-shaped curve (logistic growth) Ok so Time

02 June 2010 Populations.ppt

Logistic model Logistic model works, to a point. Real organisms have time lags for growth, time to develop eggs, flowers, etc. seasonality, longevity Real populations may exceed carrying capacity. Easter Island Pribloff Reindeer Kaibab Deer 02 June 2010 Populations.ppt

Easter Island Discovered by Polynesians ~ A.D. 1000 Population grew to several thousand Used trees for canoes to hunt dolphins Used wood for cooking Also ate birds, eggs, vegetables Resources (trees) depleted No canoes, no dolphins Warfare over land, food resources Population fell to ~ 100 when discovered by Dutch, Easter Sunday 1722. 02 June 2010 Populations.ppt

2 Life History Patterns 1. “R” Strategists short life span small body size reproduce quickly have many young little parental care Ex: cockroaches, weeds, bacteria

2 Life History Patterns 2. “K” Strategists long life span large body size reproduce slowly have few young provides parental care Ex: humans, elephants

Two general types of Life History Strategies Life History trait r-adapted, Opportunistic K-adapted, Equilibrium Offspring Many, small (high r) Fewer, large (low r) Offspring survival Low High Parental care Rare Common Reproductive age Early Later Reprod. “seasons” 1-few Many Habitat Unstable, temporary Stable, permanent Competitiveness Population regulation Density independent Density dependent Population fluctuation Irruptive Stable near K

Survivorship curves 3 types: Type 1 Type 2 Type 3 02 June 2010 Populations.ppt

Survivorship curves Type 1 Most individuals survive childhood and middle age rapidly decline in old age Example: humans 02 June 2010 Populations.ppt

Survivorship curves Type 2 Example: birds Roughly a constant mortality rate throughout individual’s life span Example: birds 02 June 2010 Populations.ppt

Survivorship curves Type 3 Most individuals will die early in life and not make it to adulthood Example: frogs, plants 02 June 2010 Populations.ppt

Life History Strategies Fluctuating populations of two interacting populations Based on pelts sold by Canadian trappers to the Hudson Bay Company, ~1840-1940. 02 June 2010 Populations.ppt