Populations

Bell Ringer A nearby high school is closing, and all their students will be coming to your high school. What will be different about your school with the addition of all these new students?

Growing Populations Increases in general populations can put stresses on resources Which resources do we protect and consume? Abundance or scarcity of food sources? Disruption of ecological systems?

Florida School Project What does the problem at Central High have to do with the environment? Do you think it is important to protect the gopher tortoise? What are some ways that building the school will affect the gopher tortoise? Do you think any living organisms were affected when (your school) was built?

What are gopher tortoises?

Gopher Tortoise Keystone species - alter the habitat by constructing and maintaining their burrows Indicator species - used as an indicator of ecosystem health.

Burrow Details Protect from temperature extremes and predators Max. length 13 m (40 feet), depth 3m (10 feet) Burrow has ledge at end where tortoise rests http://www.youtube.com/watch?v=ioOTnXSf4u0

Population Ecology A population is a group of members of the same species defined by geographic boundaries Population dynamics help ecologists understand how a population may grow or decline.

Population Dynamics Size - # of organisms Density - # of individuals with a population per unit area High population density = easier for organisms to find mates, may lead to conflict in competing for resources Low population density = organisms benefit from space & resources, difficult to locate mates.

Population Distribution/Dispersion Spatial arrangement of organisms within an area. Random = no pattern. Uniform = Evenly spaced Clumped = In groups

Sex Ratios – Proportion of males to females Age Structure – relative numbers of organisms of each age within a population Pre-reproductive Reproductive Post-reproductive

Age Pyramids Visual tools used to show the age structure

What limits population growth? Births Deaths Immigration Emigration Population change = (b + i) – (d + e)

Survivorship Graphs

Identify biotic/abiotic factors that limit population size Growth Factors Decrease Factors Abiotic Factors Biotic Factors

High reproductive rate Adequate food supply Suitable habitat POPULATION SIZE Growth factors Decrease factors Abiotic Abiotic Favorable light Favorable temperature Favorable chemical environment (optimal level of critical nutrients) Too much or too little light Temperature too high or too low Unfavorable chemical environment (too much or too little of critical nutrients) Biotic Biotic High reproductive rate Adequate food supply Suitable habitat Ability to compete for resources Ability to hide from or defend against predators Ability to resist diseases and parasites Low reproductive rate Inadequate food supply Unsuitable or destroyed habitat Too many competitors Insufficient ability to hide from or defend against predators Inability to resist diseases and parasites

Populations (r) = growth rate Population change = (b + i) – (d + e) 2 models of population growth: 1) Exponential growth: assumes ‘r’ stays constant 2) Logistic growth: as popns grow, resources diminish

Exponential population growth Under ideal conditions, a population grows rapidly (J-shaped curve)

Logistic Population Growth Unlimited resources are rare, so populations tend to level out. S-shaped curve

3 Phases in Logistic Growth Carrying Capacity The maximum stable population size a particular environment can support Occurs when Birth rate = Death rate

Bell Ringer Describe the 2 models of population growth. What is carrying capacity? Identify factors that can limit carrying capacity factors.

Carrying Capacity Limited by density-dependent factors Competition for limited resources (food, water, territory) Health (overcrowded plants produce less seeds) Physiological factors (overcrowding in field mice causes stress)

2 Types of Life Histories Strategies K-strategists: organisms live and reproduce around K, and are sensitive to population density R-strategists: organisms exhibit high rates of reproduction and live in unstable environments in which population densities fluctuate

2 Types of Life Histories Strategies K Selected - Equilibrial R Selected - Opportunistic Long life span Long maturation time Low death rate Few offspring Several reproductions per lifetime Extensive parental care Usually in stable, predictable environments Good competitors Ex: tigers, whales, elephants Short lifespan Short maturation time High death rate Usually one reproduction/lifetime Many offspring No parental care Temporary large populations followed by crashes Unpredictable changing environments Ex: insects, bacteria

Humans: R or K? From beginning to 1350 AD, humans experienced logistic growth But agriculture (food surplus), medicine, and technology expanded carrying capacity Eventually, damage to planet will decrease carrying capacity and slow human growth leading to environmental, health, food & social changes.

Human Population Growth