Ecosystems, Biodiversity, & Health – Population Ecology Dr. Bruce Wilcox Outline:

1. Ecosystems, Biodiversity, & Health – Population Ecology Dr. Bruce Wilcox Outline: • What’s population ecology about? • Population growth; exponential vs. logistic growth • Carrying capacity • Do humans obey the laws of nature?

2. Ecosystems, Biodiversity, & Health – Population Ecology Ecosystem Ecology: Focuses on a whole-systems view. The ecosystem is the primary unit of study; emphasis on energy & material cycles. Community Ecology: Focuses on interactions of species; emphasis on species’ composition and diversity. Population Ecology: Focuses on population-level processes; emphasis on population dynamics and regulation, and interspecies interactions.

3. Ecosystems, Biodiversity, & Health – Population Ecology Different subdisciplines and ways of thinking in ecology holistic “Systems thinking” “Species assemblages thinking” “Populational thinking” reductionistic (e.g., evolutionary ecology)

4. Ecosystems, Biodiversity, & Health – Population Ecology Ecosystem Ecology: Focuses on a whole-systems view. The ecosystem is the primary unit of study; emphasis on energy & material cycles. Community Ecology: Focuses on interactions of species; emphasis on species’ composition and diversity. Population Ecology: Focuses on population-level processes; emphasis on population dynamics and regulation, and interspecies interactions. Population: A group of inter-breeding organisms; All individuals of one species within an area. Population Density: The number of individuals of a population divided by the group’s occupied spatial area.

5. Ecosystems, Biodiversity, & Health – Population Ecology The fundamental principles of population growth and regulation were formalized using calculus by the physicist Alfred Lotka (1956, in Hutchinson 1978) as follows. In general the behavior of a population can be expressed as dN/dt = f(N) which simply states the rate of change of the number of individuals with time depends in some way on the number present. This becomes dN/dt=bN or N=ebt theexponential equation for population growth. Note: In the above equation b represents the unrestricted rate of increase per individual (birth rate minus death rate), called the Malthusian parameter, and accurately describes what Malthus suggested for an ideal population. Rather than b, however, r is traditionally used ecology. In the real world of resource limitations, which was the point of Malthus’ argument, population growth is eventually impeded. He reasoned that food production could only increase arithmetically and this ultimately meant starvation and deprivation.

6. Ecosystems, Biodiversity, & Health – Population Ecology

7. Ecosystems, Biodiversity, & Health – Population Ecology The population growth of organisms, including humans, potentially are limited by numerous factors besides food, athough some general patterns will be mentioned shortly. For simplicity purposes, Lotka’s exponential expression is expanded by adding a second written as dN/dt=rN(K-N/K) or N=K/1+e-rt. As an be seen from the graph of the logistic equation of population growth, N increases rapidly at first then slows down as it approaches the value of K, producing a sigmoid shaped curve. The is the simplest possible model of so-called density dependent population regulation; meaning that the population’s change varies in proportion to its size.

8. Ecosystems, Biodiversity, & Health – Population Ecology Density independent population regulation The vagaries of the physical environment can impact a population’s birth and death rates, for example: * drought * freezes * hurricane * floods * forest fires Their influence on rates of birth and death is independent of population density/size.

9. Ecosystems, Biodiversity, & Health – Population Ecology Population-Environment Theory Growth & Dispersal. When a new species emerges, population grows and can displace or replace other similar species via competitive advantage. Example: Homo sapiens 50,000-100,000 years ago migrated out of Africa and replaced populations of H. erectus and H. neanderthalensis. Exploitation Increases. Next, a population becomes large and approaches carrying capacity. Intra-specific competition becomes important. To support greater numbers, the same resources (via intensification) and/or new resources (via extensification/innovation) must exploited. This can happen via natural selection … or in the case of H. sapiens via our unique ability to innovate & invent. Example: Development of Native Hawaiian food production systems. Population Limits Reached.

10. Ecosystems, Biodiversity, & Health – Population Ecology Examples of density dependent population regulation - populations in a container or a mammal on an island!

11. Ecosystems, Biodiversity, & Health – Population Ecology Example of density independent regulation - butterflies: Size and Extinction of Natural Populations of Euphydryas editha on Serpertine Grass Habitat Patches, Jasper Ridge, California McLaughlin, John F. et al. (2002) Proc. Natl. Acad. Sci. USA 0, 52131199-99999

12. Ecosystems, Biodiversity, & Health – Population Ecology From Turner et al. Earth as Transformed by Human Action: History shows that the World’s human population growth exhibits a cycle of accelerated growth with each major technological advance, followed by a slowing of the growth rate as environmental limits are reached.

13. Ecosystems, Biodiversity, & Health – Population Ecology A new life form emerges, filling up the available resource space, following an “S” shaped (logistic) curve trajectory Population-Environment Theory Exponential curve “S” shaped or “logistic curve” Number of Individuals time

14. Ecosystems, Biodiversity, & Health – Population Ecology Once all resource space is filled, (i.e. carrying capacity is reached), there are two possible options: Population-Environment Theory Extend the resource space by colonizing a new area and repeating the pattern of exponential growth and limits 1 or Intensify use of the existing space by increasing efficiency of resource exploitation 2 time

15. Ecosystems, Biodiversity, & Health – Population Ecology Population-Environment Theory Thomas Malthus, 1798: Introduced the idea H. sapiens populations can and will reach carrying capacity (i.e. human population growth can outstrip our ability to increase food production). "The power of population is indefinitely greater than the power in the earth to produce subsistence for man”.

16. Ecosystems, Biodiversity, & Health – Population Ecology Population Ecology, Malthus and the fundamental ideas of exponential and logistic population growth and density-dependent population regulation • Essay on the Principle of Population by Malthus: • [t]he power of population is so superior to the power of the earth to produce subsistence for man, that premature death must in some shape or other visit the human race. • Large impact on science, philosophy and policy: • Influenced on policies dealing with poverty and health in England at the time, • Laid the foundation for United Nations’ population and family planning initiatives a century later. • Basis for the 20th Century “Neo-Malthusians vs. Cornucopians” population debate that persists today. Thomas Robert Malthus (1776-1834). Malthus was the first scholar to focus attention on the problem of population regulation and the limits to population growth imposed by environment.

17. Ecosystems, Biodiversity, & Health – Population Ecology Malthus influenced Darwin (& Wallace’s too) regarding origination of the theory of natural selection • Malthus’ idea of Man’s “struggle for existence” was the catalyst by which the idea of "survival of the fittest" was extended to all creatures. • Malthus’ idea of the perpetual “struggle for existence” led Darwin to recognized the significance of competition for resources within and between species. • This in turn contributed to the development of niche theory, community assembly, and other concepts and principles in population ecology as well as community ecology. Charles Robert Darwin FRS (1809 –1882). English naturalist who realized and presented compelling evidence by which evolution became an accepted by the scientific community and much of the general public in his lifetime.

18. Ecosystems, Biodiversity, & Health – Population Ecology Population-Environment Theory Esther Boserup, 1960’s: Humans increase agricultural productivity via intensification & extensification; Increased numbers of people force improvements in food production. Norman Borlaug, 1970: Nobel Peace Prize for “Green Revolution”: Combating hunger with crop technology (high-yield, disease-resistant strains).

19. Ecosystems, Biodiversity, & Health – Population Ecology Development & Collapse

20. Ecosystems, Biodiversity, & Health – Population Ecology Global population and the major human technology-driven transformations - logarithmic View from Turner et al. Earth as Transformed by Human Action.

21. Ecosystems, Biodiversity, & Health – Population Ecology Development & Collapse • ~10,000 years ago: • Development of settled agriculture • ~3,000 years ago: • Cities & empires • 1750-1950’s: • Nation states and the transition ot today’s modern industrial world

22. Ecosystems, Biodiversity, & Health – Population Ecology The majority of international efforts to address population, environment and associated conservation, development and health challenges: • 1972 Stockholm Conference (United Nations Conference on the Human Environment) - environment & economic development must be reconciled - Our Common Futuredefines “sustainable development” …. • 1992 Rio Earth Summit (United Nations Conference on Environment and Development -sustainable development articulated, Biodiversity Treaty, etc. • 2005 New York World Summit (United Nations Millennium Declaration) Millennium Development Goals - eradicate extreme poverty & disease reduction. Millennium Development Project - Investing in Development: A Practical Plan to Achieve the Millennium Development Goals, Prof. Jeffrey Sachs, Chair

23. Ecosystems, Biodiversity, & Health – Population Ecology Discussion: Do you think there is a carrying capacity of the Earth for human populations? If so, what is it?

24. Assignment, due tomorrow: Reading Assignment, due tomorrow – see website: http://www.hawaii.edu/publichealth/ecohealth/si/course-ecohealth.html “Reading for Day #4”