Population Ecology

Ecology - Study of interactions among organisms and their environment Conservation biology, environmentalism: preservation of natural world

Biosphere Ecosystems Community Population Organism Figure 1.1 ECOSYSTEM LEVEL Eucalyptus forest COMMUNITY LEVEL All organisms in eucalyptus forest POPULATION LEVEL Group of flying foxes ORGANISM LEVEL Flying fox Brain Spinal cord ORGAN SYSTEM LEVEL Nervous system ORGAN LEVEL Brain Nerve TISSUE LEVEL Nervous tissue CELLULAR LEVEL Nerve cell MOLECULAR LEVEL Molecule of DNA Figure 1.1

Population Ecology Population- how to measure? Growth rates: J shaped, S shaped K, r, and reproductive strategies Human population

How are populations measured? Population density = number of individuals in a given area or volume count all the individuals in a population estimate by sampling

mark-recapture method depends on likelihood of recapturing the same individual

The dispersion pattern of a population refers to the way individuals are spaced within their area Clumped - Uniform: Random: no pattern

Figure 35.2C

How do populations grow? Idealized models describe two kinds of population growth 1. exponential growth 2. logistic growth

A J-shaped growth curve, described by the equation G = rN, is typical of exponential growth G = the population growth rate r = the intrinsic rate of increase, or an organism's maximum capacity to reproduce N = the population size

Figure 35.3A

1500 high intrinsic rate of increase r = 0.06 1000 low intrinsic Population size zero population growth 500 r = 0 Figure: 29-06 Title: The intrinsic rate of increase (r). Caption: If the birth rate exceeds the death rate, then the population size will increase over time (r = 0.02), r = 0.06 in the example). If the birth rate equals the death rate, then the population size will stay constant (r = 0). Finally, if the birth rate is lower than the death rate, the population size will decrease over time (r = 0.05). Note what dramatic effects a small change in r can have over time, in this case on a population whose starting size is 500 individuals. negative intrinsic rate of increase r = -0.05 5 10 15 20 Time (years)

2. Logistic growth is slowed by population-limiting factors K = Carrying capacity is the maximum population size that an environment can support Figure 35.3B

logistic growth curve K = carrying capacity The term (K - N)/K accounts for the leveling off of the curve Figure 35.3C

Multiple factors may limit population growth declining birth rate or increasing death rate The regulation of growth in a natural population is determined by several factors limited food supply the buildup of toxic wastes increased disease predation

Density Dependent Factors Competition Predation Parasitism disease

Density Independent Factors Natural disasters Weather Seasonal cycles Human activities

About every 10 years, both hare and lynx populations have a rapid increase (a "boom") followed by a sharp decline (a "bust") Figure 35.5

Survivorship curves plot the proportion of individuals alive at each age Three types of survivorship curves reflect important species differences in life history Figure 35.6

Evolution shapes life histories An organism's life history is the series of events from birth through reproduction to death Life history traits include the age at which reproduction first occurs the frequency of reproduction the number of offspring the amount of parental care given the energy cost of reproduction

Principles of population ecology may be used to manage wildlife, fisheries, and forests for sustainable yield reverse the decline of threatened or endangered species reduce pest populations

The Spread of Shakespeare's Starlings In 1890, a group of Shakespeare enthusiasts released about 120 starlings in New York's Central Park

Today: over 100 million starlings, spread over N. Amer. Current 1955 Current 1955 1945 1935 1925 1945 1905 1915 1925 1935 1925 1935

The starling population in North America has some features in common with the global human population Both are expanding and are virtually uncontrolled Both are harming other species

Why We Live in Interesting Times… Pre 2000 A.D. More youth than elderly More rural than urban Post 2010 A.D. More elderly than youth More urban than rural People alive 1950-2050 A.D. have seen: Highest growth rate (2.1%/year) Population double during their lifetime More people have lived in the last 100 years, than in all of human history before 1900!

“An Essay on the Principle of Population” Thomas Malthus (1798) “An Essay on the Principle of Population” Populations grow geometrically while supporting resources grow arithmetically Population, if not purposefully checked (“preventative checks”), would outpace resources and lead to unplanned “positive checks” that would return population to sustainable levels

HUMAN POPULATION GROWTH Earth's population: 6 billion (Oct 12, 1999) Every second, five people are born and two people die, a net gain of three people. Every day, +250,000 = 2 x Champaign-Urbana This year, +87,000,000 = Mexico This decade +1,000,000,000 = China

THE HUMAN POPULATION doubled three times in the last three centuries about 6.1 billion and may reach 9.3 billion by the year 2050 improved health and technology have lowered death rates

The history of human population growth Figure 35.8A

Also reveals social conditions, status of women The age structure of a population is the proportion of individuals in different age-groups RAPID GROWTH SLOW GROWTH ZERO GROWTH/DECREASE Kenya United States Italy Male Female Male Female Male Female Ages 45+ Ages 45+ Ages 15–44 Ages 15–44 Under 15 Under 15 Percent of population Percent of population Percent of population Also reveals social conditions, status of women Figure 35.9B

The ecological footprint represents the amount of productive land needed to support a nation’s resource needs The ecological capacity of the world may already be smaller than its ecological footprint

Ecological footprint in relation to ecological capacity Figure 35.8B

Per capita CO2 emissions (metric tons of carbon) Total CO2 emissions (billion metric tons of carbon) 1 2 3 4 5 6 0.5 1 1.5 U.S. 5.48 U.S. 1.49 China 0.75 China 0.91 Russia 2.65 Russia 0.39 Japan 2.51 Japan 0.32 India Figure: 29-14ab Title: Use of resources per person. Caption: The use of natural resources per person (or “per capita”) varies greatly from one country to the next. The average resident of a developed country, such as the United States, uses far more resources than the average resident of a less-developed country, such as India, and this has environmental consequences. (a) One measure of resource use is per-capita carbon dioxide (CO2) emissions: the amount of CO2 a country releases into the atmosphere through human-caused activities, divided by the number of people that country has. The graph displays per-capita CO2 emissions for five countries in 1997, as measured in metric tons of carbon. (b) The differences in per-capita emissions have significant consequences for total emissions within a country. In 1997 the United States released twice as much CO2 into the atmosphere as China, even though it had only one-fifth as many people as China. 0.29 India 0.28

What next?

Figure 2.10x