Population Understanding populations The Human Population Biodiversity

What is a population?  Population – All the members of a species living in the same place at the same time.  EX: All of the bass in an Iowa lake make up one population.

Properties of Populations  Density – the number of individuals in a certain space  Dispersion – is the relative distribution or arrangement of its individuals within a given amount of space  Size- number of individuals  Age distribution- proportions of individuals of each age

What Limits Population Growth?  There are 4 variable that limit population growth.  Births  Deaths  Immigration  Emigration  A population gains individuals through births and immigration and loses them by death and emigration.

Population Growth  Growth Rate = The birth rate minus the death rate. Growth rateBirthsDeaths

 A population will remain the same size if the number of deaths are replaced by the same number of births.

How Fast Can a Population Grow?  Reproductive Potential: the maximum number of offspring that each member of the population can produce.  Darwin calculated it would take elephants 750 years to produce 19 million descendants. Bacteria can do that in a few days.

Reproductive Potential cont.  Increases when individuals produce more offspring at a time, reproducing more often and earlier in life.  Reproducing earlier shortens the generation time – the average time it takes a member of the population to reach the age when it reproduces.  Typically smaller organisms have a smaller generation time than larger organisms.

How Fast Can a Population Grow?  Exponential Growth – growth occurs faster and faster.  Occurs in populations when there is plenty of food, water and space available and little or no competition or predators

Environmental Limits on a Exponential Growth  Natural conditions are neither ideal or constant, so populations don’t normally continue to grow exponentially.  Only some members of a population will grow and reproduce, the properties of a population may change over time.

Carrying Capacity (K)  The carrying capacity (K) of an ecosystem for a particular species is the maximum population that the ecosystem can support.  An ecosystem may go above this number but it will never stay there

Resource Limits  When a population consumes a particular resource at the same amount that the ecosystem can produce the resource it limits the population.  EX: plant growth is limited by water, sun and minerals

Competition  The members of a population use the same resources in the same way so they will eventually compete.  Food  Territory  Social Dominance  Light  Shelter  Water

Two types of population regulation  Density Dependent – Deaths occur more quickly when the population is more dense or greater in size. Ex. Disease or pest infestation  Density Independent – When a certain portion of the population dies regardless of its size.  Ex. Severe Weather or natural disasters

How species Interact With Each Other  What is the difference between lions at the zoo versus lions in the wild?  Wild:  Lions are a part of a food web  Hunt zebras  Fight with hyenas  Fed upon by fleas and ticks

Niche  Niche – the unique role of a species within an ecosystem.  A Niche includes:  Physical home  The environmental factors needed for survival  All of the interactions with other organisms.

Habitat vs. Niche  Habitat is where the organism lives  Niche is the patterns of use of its habitat.

Interactions between species  There are five major types of species interaction.  Competition  Predation  Parasitism  Mutualism  commensalism

Competition  When different individuals attempt to use the same limited resources.

 Competition can occur within and between species  Competition occurs within the same species because those organisms all have the same niche.  When competition occurs between species we say that those species niches overlap.

Adaptations to Competition  When two species with niches that overlap compete sometimes the better adapted species survives and the other does not.  Competition can be reduced by niche restrictions  Using less of the area  Using resources at different times

Predation  An organism that feeds on another organism is a predator  An organism that is fed on is prey

Symbiosis  Any relationship where two species live in a close association

Examples of Symbiosis: Parasitism  An organism that lives in or on a host is a parasite  Ex: ticks and dog heart worm

Examples of Symbiosis: Mutualism  A close relationship where both species benefit each other.

Examples of Symbiosis: Commensalism  A relationship where one species benefits and the other is neither harmed nor helped

Commensalism

Coevolution  Over time, species in close association may (think symbiosis) coevolve.  These species may evolve together.