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Populations Interdependence in Nature Chapter 5 Describing Populations • Group of organisms of a single species that lives in a given area • Studied by – Geographic range – Density and distribution – Growth rate – Age structure Describing Populations • Geographic range – The area inhabited by a population (where they live) – Native (natural) range vs. introduced range • Hydrilla • Zebra mussels • Density and distribution – Number of individuals per unit area – Three general types • Random • Uniform • clumped Describing Populations • Growth Rate – Determines whether the size of a population increases, decreases or stays the same • Age structure – The number of males and females of each age a population contains Population Growth • Birthrate vs. death rate – Higher birthrate – population grows – Higher death rate – population shrinks – Equal rates – zero growth • Immigration vs. emigration – Imm- growth caused by moving in from elsewhere – Em- decline caused by leaving a population range Types of Growth • Exponential Growth – The larger a population, the faster it grows – Under ideal conditions with unlimited resources, populations will grown exponentially – Causes a J-shaped curve when graphed • Logistic Growth – Phases of growth • Exponential • Growth slows • Growth stops – Causes an S-shaped when graphed – Carrying capacity – the maximum number of individuals of a particular species a particular environment can support Limits to Growth • Limiting factors – controls the growth of a population – Determine the carrying capacity of an environment Two types of limiting factors • Density-dependent – – – – – – Competition Predation Herbivory Parasitism Disease Stress from overcrowding • Density-independent – Unusual weather – Natural disaster Human Population Growth • Tends to increase – Rate of increase has changed over time – Causes of increase – advance of civilization Patterns of Human Population Growth • Demography – study of human populations – Looks at the characteristics of human population – Tries to explain how populations will change over time