Chapter 14: Populations Section 14-1: Populations and How They Grow

Changing Populations A population is a group of organisms of a single species that live in a given area. In nature, populations can grow, shrink, or stay the same from year to year. A population will change size depending on how many organisms are added to it and how many organisms are removed from it.

Growth Rate The change in population size is called growth rate – and it can be: Negative - more organisms removed than added Positive - more organisms added than removed Zero - the same number of organisms added that are removed

Growth Rate Zero growth rate does not mean zero change – it means zero NET change All organisms are interconnected via food webs, so growth rate of a population depends on how organisms interact

Why do populations grow? If you provide any population with ideal conditions, it will increase in size because healthy organisms will always reproduce faster than their death rate Generally, if birth rate is higher than death rate, the population will increase (grow)

Three Types of Growth Unless something stops them, populations tend to increase There are three growth curves: – Exponential growth – Growth with limits – Boom and bust

Exponential Growth When population experiences ideal conditions and grows faster the larger it gets Ideal conditions include adequate food supply, protection from predators, shelter Ex: Bacteria

Exponential Growth Population increases at a faster rate the larger it gets

Growth With Limits Exponential growth cannot continue indefinitely – usually slows down At some point, birth rate and death rate population become the same, and population growth stops Called zero population growth – does not mean that the number of individuals in the population is zero, but that the size of the population remains the same – called the steady state

Growth With Limits Carrying capacity is the largest number of individuals that can survive over long periods of time in a given environment. If the population gets larger than carrying capacity, either birth rate falls or death rate rises If the population falls below carrying capacity, birth rate rises, death rate drops, or both occur

Growth With Limits At some point, birth rate and death rate become equal and carrying capacity is reached – this is called steady state

Boom and Bust Some species grow until they reach a peak population size (the boom) and then crash dramatically (the bust) After the crash, the population may begin to grow again right away, or it may stay low for a period of time

Boom and Bust Species grow until they reach a peak population size (the boom) and then crash dramatically (the bust)