Populations and Communities Holt ES Ch. 8.1

Population: a group of organisms of the same species that live together in one place at one time and interbreed. Population growth is important because populations of different species (including humans) interact in communities Population: a group of organisms of the same species that live together in one place at one time and interbreed. Population growth is important because populations of different species (including humans) interact in communities

Populations can be described 3 ways;  Size  Total number of individuals  Density  # individuals per unit Area  Dispersion  Arrangement in space  Even, clumped, random  Size  Total number of individuals  Density  # individuals per unit Area  Dispersion  Arrangement in space  Even, clumped, random

Dispersion

Population growth depends on 4 factors: 1.Births 2. Deaths 3. Immigration (movement of individuals into a population) 4. Emigration (movement of individuals out of a population) 1.Births 2. Deaths 3. Immigration (movement of individuals into a population) 4. Emigration (movement of individuals out of a population)

Biotic Potential  Fastest rate at which a population can grow… depends on …  reproductive potential --- The maximum number of offspring that each member can produce  Fastest rate at which a population can grow… depends on …  reproductive potential --- The maximum number of offspring that each member can produce

Reproductive potential  Varies widely: flies vs. whales  Higher when individuals  Produce more offspring at a time  Reproduce more often  Reproduce earlier in life  Greatest effect because it shortens generation time  Varies widely: flies vs. whales  Higher when individuals  Produce more offspring at a time  Reproduce more often  Reproduce earlier in life  Greatest effect because it shortens generation time

Reproductive strategies  R strategy – where biotic and abiotic factors fluctuate  K strategy – where biotic and abiotic factors are more stable  R strategy – where biotic and abiotic factors fluctuate  K strategy – where biotic and abiotic factors are more stable

Characteristics of r- and K-selected organisms  r-organismsK-organisms  short-livedlong-lived  smalllarge  weakstrong or well-protected  waste a lot of energyenergy efficient  less intelligentmore intelligent  have large littershave small litters  reproduce at an early agereproduce at a late age  fast maturationslow maturation  little care for offspringmuch care for offspring  strong sex driveweak sex drive  small size at birthlarge size at birth  Note: Not all characteristics apply to all organisms.  Cybernetica,  r-organismsK-organisms  short-livedlong-lived  smalllarge  weakstrong or well-protected  waste a lot of energyenergy efficient  less intelligentmore intelligent  have large littershave small litters  reproduce at an early agereproduce at a late age  fast maturationslow maturation  little care for offspringmuch care for offspring  strong sex driveweak sex drive  small size at birthlarge size at birth  Note: Not all characteristics apply to all organisms.  Cybernetica,

Two kinds of population growth:  Exponential  logistic  Exponential  logistic

Exponential growth  Numbers increase by a certain factor in each time period  J-shaped graph  Lag time  Numbers increase by a certain factor in each time period  J-shaped graph  Lag time

Logistic growth  Begins with a minimum number of individuals and reaches a maximum at the carrying capacity of the habitat  S - shaped graph  Lag time  Begins with a minimum number of individuals and reaches a maximum at the carrying capacity of the habitat  S - shaped graph  Lag time

Carrying capacity  The maximum population an environment can support at any given time

Actual logistic growth

Logistic growth curve

Factors affecting population size  Abiotic factors: Weather, climate  Biotic factors: food predators disease parasites humans

Density-dependent factors limiting growth number of individuals  Variables that are affected by the number of individuals present  Ex: availability of nest sites, food, water,competition, migration number of individuals  Variables that are affected by the number of individuals present  Ex: availability of nest sites, food, water,competition, migration

Density-independent factors affecting growth regardless of population size  Variables that affect a population regardless of population size  Ex: weather, flood, fire regardless of population size  Variables that affect a population regardless of population size  Ex: weather, flood, fire