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Population Ecology

Discover the intricate world of population ecology, from density and distribution to factors driving human population growth. Explore exponential and logistic growth models, study population limiting factors, and delve into the dynamics of invasive and endangered species. Uncover the nuances of population interactions and understand how biotic and abiotic factors influence population size. Learn about human population growth trends and the impact of factors like industrialization and healthcare. Dive into the complex web of population dynamics and understand the delicate balance that governs ecosystems.

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Population Ecology

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  1. Population Ecology • 1. Density and Distribution • 2. Growth • a. Exponential • b. Logistic • 3. Population Limiting Factors • 4. Human population growth

  2. Examples of applications • Invasive species • Endangered species • Pest control (e.g., agriculture) • Human population growth

  3. Population. Individuals of same species occupying same general area. Density: the number of organisms in a given area Distribution: how the organisms are spaced in the area

  4. Changes in population size Northern Pintail Duck Growing Shrinking Fluctuating

  5. Questions • Why do populations change in size? • What factors determine rates of population growth or decline? • How do these differ among species?

  6. 2. Population growth • Two models of population growth: • Exponential • Logistic

  7. 2. Population Growth a. exponential growth The change in population size (N) in an interval of time is number of births – number of deaths, or ∆N = B - D ∆t (ignoring immigration and emigration) If b (birth rate) is the number of offspring produced over a period of time by a population, and d (death rate) is the average number of deaths for that population, ∆N = bN – dN or∆N = (b – d)N ∆t ∆t

  8. Population Growth: exponential growth The difference between the birth rate and the death rate is the per capita growth rate r = b - d The growth equation can be rewritten as ∆N = rN or dN = rN ∆t dt Exponential growth occurs when resources are unlimited and the population is small (doesn’t happen often). The r is maximal (rmax) and it is called the intrinsic rate of increase.

  9. r can also be negative (population decreasing) if r is zero, the population does not change in size thus, the rate of increase (or decrease) of a population can change over time.

  10. Exponential growth does not happen often:

  11. Or indefinitely: Reindeer on the Pribalof Islands, Bering Sea reindeer slide

  12. 2.b. Logistic growth Most populations are limited in growth at some carrying capacity (K) (the maximum population size a habitat can accommodate)

  13. Logistic Growth Equation: incorporates changes in growth rate as population size approaches carrying capacity. dN = rmaxN dt (K - N) K

  14. r- and K-selection K-selection Near carrying capacity natural selection will favor traits that maximize reproductive success with few resources (high densities). Density-dependent selection. r-selection Below carrying capacity natural selection will favor traits that maximize reproductive success in uncrowded environments (low densities). Density-independent selection.

  15. Density-dependent Any characteristic that varies according to a change in population density. Density-independent Any characteristic that does not vary as population density changes. food availability, territories, water, nutrients, predators/parasites/disease, waste accumulation weather events, salinity, temperature

  16. 3. Factors that limit population growth • Density dependent birth and death rates. Many of these reflect • competition for resource (food/energy, nutrients, space/territories). • predation, parasites, disease • waste accumulation (e.g., ethanol)

  17. 4. Factors that limit population growth • Density independent survivorship or mortality • Extreme weather events • Fluctuations in wind and water currents

  18. Interactions among population-limiting factors The dynamics of a population result from the interaction between biotic and abiotic factors, making natural populations unstable. Water temperature, Competition, Cannibalism.

  19. Population-Limiting Factors Some populations have regular boom-and-bust cycles. Predation Food shortage in winter Prey availability

  20. SUMMARY Population. Individuals same species occupying same general area. Have geographic boundaries and population size. Key characteristics Density. Individuals per unit of area or volume. Distribution: uniform, clumped, random. Demography. Studies changes in population size. Additions (+) : Births and Immigration. Subtractions (-) : Deaths and emigration. Life histories. Affect reproductive output and survival rate and thus population growth. Life history strategies are trade-offs between survival and reproduction.

  21. Population Growth Exponential. J-shaped. Idealized, occurs in certain conditions. Logistic. S-shaped. A little more realistic. Carrying capacity. K-selection. Density-dependent selection. r-selection. Density independent selection. Population growth is slowed by changes in birth and death rates with density. Interaction of biotic and abiotic factors often results in unstable population sizes. In some populations they result in regular cycles.

  22. 4. Human population growth

  23. Human Population= 6,596,469,500 (earlier today) Exponential growth since Industrial Revolution: better nutrition, medical care and sanitation. Growth rates ( r ) 1963: 2.2%(0.022), 1990: 1.6%, 2003: 1.3% (200,234/day), 2015: 1% http://www.ibiblio.org/lunarbin/worldpop Growth will slow down either due to decreased births or increased deaths. Likely both as suggested by age-structure pyramids: relative number of individuals in each age-class.

  24. When and how will human population growth stop? • This question is likely to be answered one way or another in your lifetime. • What is Earth’s carrying capacity for human’s? • Have we already exceeded K? • What are consequences of human population growth for other species on this planet?

  25. Human impact • Depends on • Total human population • Consumption by each individual • Ecological impact of each unit of consumption • I = PAT (Ehrlich and Ehrlich) • P = population • A = affluence • T = technology

  26. Unknown what the carrying capacity of Earth for humans is. A useful concept is the ecological footprint: land needed to produce resources and absorb wastes for a given country. World Wildlife Fund for Nature

  27. Ecological footprints for various countries and the world

  28. SUMMARY Human population has been growing exponentially for a long time. A reduction is expected either through lower birth rates or higher death rates. The age-structure suggest different scenarios for individual countries. Humans appear to be above Earth’s carrying capacity.

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