Chapter 4 Population Biology

What is a population? Group of organisms, all of the same species that live a specific area

How fast do populations grow? Increase slow at first, then faster because there are more reproducing individuals Populations do not increase forever Populations will level out due to limited factors Examples of limited factors: predation, disease, lack of space, food supply

Exponential Population Growth

Let's look at the graph in your book on pg. 94

Population Growth Graph J-shaped curve showing exponential growth of a population This population has not yet reached its carrying capacity. S-shaped curve shows how a population becomes limitied by environmental factors Carrying Capacity: the maximum size of a population that an area can support

Population Growth Steady State Carrying Capacity Exponential Phase Lag Phase

Carrying Capacity The number of organisms of one species that an environment can support indefinitely Developing environment: more births than deaths and the population increases until it reaches its carrying capacity When it reaches carrying capacity, more deaths than births due to limited resource Population fall below carrying capacity again

Limiting Factors Any biotic or abiotic factors that restricts the existence, numbers, reproduction or distribution of organisms. Ex. Soil, food, organism, strong winds, temperatures, high elevations, water

Tolerance Ability of an organism to withstand fluctuations in biotic and abiotic environmental factors Example: too much water or too little water on corn plants

Ranges of Tolerance Range over which a population or organism can successfully survive and grow Too much or too little of an environmental factor can be limiting

What affects population density What affects population density? Population density: number of individuals in a given area Density-dependent factors: affect the size of a population and depend on the size of that population Examples: disease, predation, parasites, limited resources, competition, stress from overcrowding Density-Independent Factors: affect the size of a population but do not depend on the size of that population Examples: volcanic eruptions, temperature, storms, floods, droughts, chemical pesticides

Organism interactions limit populations size Population size are not limited only by abiotic factors Examples: Predator-Prey Relationships, Competition

Predator-Prey Relationships Predation can be a limiting factor on population size Predator-Prey relationships show a predictable cycle of population increases and decreases over time

Competition within a Population What happens when organisms within the same population compete for resources?

DEMOGRAPHY The study of human population size, density, and distribution, movement, and its birth and death rates Factors that have lead to human population living longer and producing offspring that live long enough to produce offspring Vaccines Producing more food Technology to supply clean water Infant mortality rate decrease

Calculating growth rate Birthrate: number of live births per 1000 Death rate: number of deaths per 1000 Immigration: movement of individuals into a population Emigration: movement of individuals out of a population Birthrate – Death rate = Population Growth Rate (PGR) PGR above zero population is growing PGR below zero, fewer individuals are enter than leaving

Age Structure Graph

Age Structure Graph

Ways To Estimate Populations 1. Random Sample 2. Mark & Recapture