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This article discusses population ecology, including factors that influence population growth, the effects of population size and density on the environment, and the concept of limiting factors. It also explores population growth rates, birth and death rates, and different population growth patterns. Additionally, it covers limiting factors and their impact, both biotic and abiotic, and provides case studies on predator-prey relationships and irruptive growth.
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CPES Ecology Part II Population Ecology 2008-09
Populations - Topics to be Discussed • Populations either • grow • decline • stay the same • What influences the growth of a population? • How does population size, density, and growth affect an organism’s environment?
Population Ecology Definitions • population • biotic potential • environmental resistance(limiting factors) • population density • carrying capacity • predators and prey • parasites and host • limiting factors • Density-dependent • Density-independent • competition • intraspecific • interspecific
Population Growth Rate • Birth Rate: births/popn at beginning • Death rate: deaths/popn at beginning • Growth rate = birthrate-deathrate • Example • Population of 5000 on Jan 1 • Births 400 throughout year • Deaths 100 throughout year • What is Birthrate and deathrate? • How many added to this population this year • Calculate number added if population were 100,000 at beginning of year instead of 5000 • Answers: BR=8%; DR =2%; GR=6% • Popn 100000 added is 6000
Rate of Growth – Births • What would affect number of births in a population? • Number of young in each “litter” • Examples of high and low number?? • How often have young • Examples of seldom vs. often • Age at which females start having young • Rodents vs. elephants
Rate of Growth – Deaths • What would affect number of deaths in a population? • Lifespan • Outside environmental factors – limiting factors
Population Growth Curves • Exponential growth • S-curve • Carrying capacity • limiting factors • Population explosions (11) - irruptive growth pattern
Exponential vs. Arithmetic Growth • Arithmetic: constant amount per time unit • Independent of population size • Exponential: increases by constant fraction, or exponent, by which current population multiplied • Actual number of organisms added dependent on population size • Power of biological reproduction • Rate constant, but number added changes: “Compound interest”
Limiting factors affecting population - biotic or density dependent Food, predators, disease, human activity • bluebirds • predators and PA deer (8) • succession - PA forests and grouse (8) • habitat fragmentation • habitat loss • Case studies • Predators - a Natural Balance? (1.3) • The case of the missing hawks (1.4) • Coyotes - opportunistic omnivores (1.5)
Limiting factors affecting population - abiotic or density independent • Climate and weather • Soil (mineral components) • Slope (% and direction) • Oxygen content of water • Aquatic - type of bottom
Irruptive Growth • Rapid exponential growth (J curve) followed by population crash • Population surpasses carrying capacity • Death rate exceeds birthrate • Are there some organisms for which this is normal? • Yes! • What are some examples?
Do some populations “limit” their own growth • Territoriality • Levels of fertility • may depend on food supply • Why might this be an advantage for the population? • What process may have resulted in such “intrinsic” limiting factors?
Predator and Prey Relationships • Do predators destroy a prey population, resulting in declines and possible extinction? • Do predators actually benefit the prey population? • What is the relationship between predators, prey, and habitat?
Isle Royale - Wolves and Moose • What caused 1930 crash in moose population? • Why did the moose not decrease their population before the crash occurred? • Why did the predators not exterminate the moose population? • What happened when the wolf population declined in the 1980s?
