Ecologists work at many scales

Populations

Populations Groups of organisms of the same species that live within a given area

Population Characteristics We can characterize individual populations in terms of Variation Patterns of Dispersion Demographics Size and Density Limits on population growth Human population growth

Members of a population show similarities because they belong to the same species.

Members of a population also show variation. Most variation falls in a normal distribution (bell-shaped frequency).

Population Characteristics We can characterize individual populations in terms of Variation Patterns of Dispersion Demographics Size and Density Limits on population growth Human population growth

There are three common patterns of population distribution: Uniform

Why Different Types?

Population Characteristics We can characterize individual populations in terms of Variation Patterns of Dispersion Demographics Size and Density Limits on population growth Human population growth

Demographics Characteristics of a population Examples: Average age Average size Average number of offspring http://quickfacts.census.gov/qfd/states/53000.html

Population Characteristics We can characterize individual populations in terms of Variation Patterns of Dispersion Demographics Size and Density Limits on population growth Human population growth

Four Factors Influence the Size of a Population: Natality: Birth Rate (offspring produced and added to population)

Mortality: Death Rate (individuals that die)

Immigration: Movement of members of the species into the area

Emigration: Movement of members of the species out of area to live elsewhere.

Population Change Population Change = (natality + immigration) (mortality + emigration)

Exponential Curve Unlimited Growth (J-Shaped) Populations tend to grow in size for the simple reason that individuals tend to have more than one offspring.

Can this happen in nature? Yes: Bacteria If there are no factors limiting the growth, their number will increase rapidly.

Exponential growth of bacteria

Can this happen in nature? Yes: Invasive species Uniform habitat No predators No disease Unlimited area Abundant food

Pythons

Logistic Curve Limited Growth (S-Shaped) 3 Phases: 1. Exponential growth Phase 2. Transitional Phase 3. Plateau Phase

Exponential Growth Phase Population increases exponentially. Resources are abundant. Predators and disease are rare.

Transitional Phase As a result of intra-specific competition for food, shelter, nesting space, etc., and the build up of waste. The growth rate slows down. Birth rates decline and death rate increases

Plateau Phase Natality and mortality are equal so population size is constant. When the number of individuals in the population have reached the maximum which can be supported by the environment. The number is called the CARRYING CAPACITY

Growth of a population of fur seals

Population size oscillates around the carrying capacity (K) overshoot K N oscillations Time

Population Characteristics We can characterize individual populations in terms of Variation Patterns of Dispersion Demographics Size and Density Limits on population growth Human population growth

Limits on Population Growth Water and shelter are critical limiting factors in the desert. Density Dependent Limits Food Water Shelter Disease Density Independent Limits Natural Disasters Humans (logging, mining, farming) Fire is an example of a Density independent Limiting factor.

Population Characteristics We can characterize individual populations in terms of Variation Patterns of Dispersion Demographics Size and Density Limits on population growth Human population growth

World Population Events Time unit Births Deaths Growth ------------------------------------------------- Year 131,571,719 55,001,289 76,570,430 Month 10,964,310 4,583,441 6,380,869 Day 360,470 150,688 209,782 Hour 15,020 6,279 8,741 Minute 250 105 146 Second 4.2 1.7 2.4 -------------------------------------------------

What s Behind Population Growth Three Factors Fertility Infant Mortality Longevity Animal Domestication and Agriculture Provided for a few to feed many Industrial Revolution Growth of Cities and Infrastructure Water Energy Transportation Increased Productivity Nutrition Sanitation Medicine

Age structures of three nations Shrinking Growing Stable Are these growing, shrinking or stable populations?

Exponential growth of the human population Limited Human resources population eventually growth will cause does human not currently population show growth density to slow, effects that typically but characterize global human natural populations. carrying capacity is not known.

Population Predictions Most predictions: 9-12B by 2050 10-15B by 2100 Large uncertainties

Land Resource Limits Deforesting to acquire more arable land Would run out in next century at current yields Water In 1950 people used half of accessible water Are now dependent on dams Pollution loses 33% of potential water Getting close to limits Energy growth very high last fifty years Mostly hydrocarbon fuels Nonrenewable resource consumption Climate change issues

Question: Why are humans destroying the earth? destructamundo destructamundo destructamundo destructamundo

Question: Why do locusts destroy crops? nymph aggregating nymphs adults feeding swarming destrutamundo

Limits: Locust Freedom Without Responsibility I ve got my rights! It s a free country! = Destroyed Crops (destruction of environment) Who s going to stop me?

Phage et al. Question: Why do some microbes make us sick?

Limits: Pathogen Freedom Without Responsibility It s a free country Who s going to stop me? I ve got my rights! Bacterial pathogens = Disease! (destruction of the body environment)

Question: Why are humans destroying the earth? destructamundo destructamundo destructamundo destructamundo

Human Freedom Without Responsibility lack of cooperation the bottom line It s a free country pesticides loss of habitat overfishing out-of-control materialism bigger is better global warming deforestation loss of topsoil overconsumption conspicuous consumption destruction might makes right TEOTWAWKI = the end of the world as we know it Who s going to stop me? radical anti-environmentalism I ve got my rights! loss of farmland overpopulation = Destructamundo! (destruction of environment) special interests short-term thinking air polution greed NIMBY = not in my backyard urban sprawl fish kills toxic algal blooms loss of wetlands greenhouse effect monoculture desertification erosion ozone hole water polution mass extinction lack of cooperation

Humans need to be better ecologists.