Why does the US Government conduct a census every 10 years? Populations Why does the US Government conduct a census every 10 years?

What causes populations to grow? What contributes to fast or slow growth of a population?

Population – all individuals of a species that live together in 1 place at 1 time 3 key features of populations: 1. size – # of individuals – if small, risk extinction (disaster & little genetic variation)

2. density - # of individuals in an area 3. dispersion – how individuals are arranged

Population Ranges A species might not be able to expand its population range because it cannot survive the abiotic conditions found in the expanded region. Common dolphin Pupfish

Population-Limiting Factors There are two categories of limiting factors—density-independent factors and density-dependent factors.

Density independent factors – weather, fire, climate, pollution & human alteration of landscape can affect growth Any factor that does not depend on the # of members in a population

Density-Dependent Factors Any factor in the environment that depends on the #of members in a population Biotic factors Disease Competition Parasites

Growth=more births than deaths Exponential growth curve = rate of population growth stays the same Carrying capacity- the population size an environment can sustain (limiting resources – water, food- density dependent factors) When a population is below the carrying capacity, the birth rate is high, when the population is at the carrying capacity, the death rate is high

All populations grow exponentially until some limiting factor slows the growth.

Carrying capacity is limited by the energy, water, oxygen, and nutrients available.

A population stops increasing when the number of births is less than the number of deaths or when emigration exceeds immigration.

The rate strategy, or r-strategy, is an adaptation for living in an environment where fluctuation in biotic or abiotic factors occur. An r-strategist is generally a small organism. Short life span Produces many offspring

The carrying-capacity strategy, or k-strategy, is an adaptation for living in stable environments. A k-strategist is generally a larger organism. Long life span Produces few offspring