Population Biology Populationslarge and smallchange over time Meaning

Population Biology

Populations—large and small—change over time Meaning, they are DYNAMIC Humans face similar problems as small or large populations that other organisms do BUT humans also have an advantage What is our advantage?

We know populations interact…

Prey Herbivore-carnivore populations may Bay increase, Lynx and. Prey Hare Pelts Sold to the Hudson’s Company followed by increases in predator populations, Number of organisms(in thousands) followed by decrease in prey populations, followed by decrease in predator populations Times (in years)

Predators Results in the fates of predator and prey populations being intimately intertwined. Population size fluctuates due to this relationship Preying most successfully on the Slowest Weakest Least fit members of their target population

Predators affect populations Preventing excess population growth Allowing successful traits to become dominant in the prey population (and the predators) Sounds like…unscramble the phrase below TAURALN TNIOLEESC Predation may lead to extinction Seen with introduced species. Two categories of predator-prey relationships. Intraspecific and interspecific…more later

Herbivore vs. Producer Herbivores have developed adaptations to deal with fluctuations in available food supplies: Put on extensive layers of fat during seasons of abundance. Some will migrate to where food is available. Others hibernate during seasons of hardship. Respond to seasons of scarcity by making do with foods of relatively low nutritional value.

Plants are Prey too… Plants respond to herbivores by: Producing enough tissue for herbivores and still survive Produce distasteful chemicals that deter further feeding Produce chemicals that affect herbivores’ physiology

Herbivore-Carnivore Interactions Compared to plant material, animal material is Easier to digest Energy and nutrients are more concentrated Drawback: Herbivores are mobile Dangerous when cornered Mimicry

Competition Intraspecies—arising or occurring within a species; involving the members of one species INTRA— m o n g u s Remember—hyenas compete with each other for rank (hierarchy), food, mating rights and territory

Plants have developed mechanisms to cope with intraspecific competition. Seedlings unable to germinate in the shady conditions created by parent plants. Plants disperse seeds to other sites by water, air, or animals. Plants secrete substances that inhibit the growth of seedlings near them.

Animals have developed mechanisms to cope with intraspecific competition. Varied life cycles different habitats and feeding in juvenile and adult invertebrates Occupy different ecological niches. Territoriality: intense intraspecific competition define an area surrounding their home site/nesting site defend it.

How would this help the population (increase survival)? ? ? Help allocate resources of an area by spacing out the members of a population Promote dispersal into adjacent areas

Competition Interspecies—existing or occurring between species b INTER— t w e e n 2

When Populations Compete, Both are Harmed Law of competitive exclusion: no two species will occupy the same niche cannot compete for exactly the same resources in the same habitat for very long One species will have a competitive edge gain a larger share of resources. Other species will migrate to a new area, become extinct, or change its behavior in a way to minimize competition.

Competition may cause competitive exclusion, the elimination of one species in a community. Examples: • Paramecium • Wasps • Barnacles

Factors That Influence Population Size Population growth rate Determined by: Natality or birth rate Death rate Also influenced by immigration and emigration. Expressed mathematically: r = (b-d) + (i-e)

When Studying Populations… Count up all the individuals in the population. Why is that impractical? More frequently used is density. The number of individuals per unit area.

Labs… Random Sampling A method of selecting a sample Random means Sample means How does it work? BEST for STATIONARY POP (pic of or plants!!!)

Mark and Recapture Sample where animals are caught alive and tagged and then returned (unharmed) to their habitat over time animals from the pop are trapped and those with marks/tags are counted mathematical formula estimates the pop size

Next How do scientist collect data on population size?

Population Growth J-Curve Exponential Growth Unchecked growth As a population gets larger it grows faster

Population Growth S-Curve Carrying capacity Number of organisms the environment can support Limiting factors Biotic abiotic

What often happens…

Population Size Assumptions Perils of Small Populations low genetic diversity subject to inbreeding less likely to adapt to environmental changes Problems being a Large population Increase food shortages & diseases Decrease in space, clean water Live at carrying capacity so can experience huge crash Adaptable with greater genetic diversity

Population Density Population density is total population size per unit of area. Population densities depend on: Interactions within the environment Quality of habitat Density dependent factors Density independent factors

Dispersion Patterns Within Populations Three common patterns of population distribution are:

Population Density Uniform Clumped Random

Population Density-dependent factors Disease Competition Predators Parasites food Density-independent factors Volcanoes Temperature Storms Floods Drought Habitat disruption

Population Stress As populations increase in size = variety of stress symptoms aggression, decrease in parental care, decreased fertility, and decreased resistance to disease. become limiting factors for growth and keep populations below carrying capacity

Patterns Reproductive pattern = life-history pattern Variety of patterns Two extremes

Patterns Rapid life-history patterns Changing or unpredictable environment Small Mature rapidly Reproduce early Short life span

r-selected Reproductive Strategy r-selected Species: have high reproductive rates tend to occur in unpredictable environments typically have type III survivorship curves

Patterns Slow life-history pattern Large species Stable environments Reproduce slowly Matures slowly Long life span Stay at or near carrying capacity

K-selected Reproductive Strategy K-selected Species: occur near carrying capacity experience effects of population density have low reproductive rates, high parental care have type I survivorship curves.

Survivorship in Populations

Reproductive Strategies r- Selected (maximum growth rate, below carrying capacity) Early reproduction Short life span High mortality rate Little or no parental care Large investment in producing large numbers of offspring Below carrying capacity Examples: Bony fish Grasshoppers K-Selected (maximizes population size near carrying capacity) Late reproduction Long life span Low mortality rate Extensive parental care Greater investment in maintenance and survival of adults At or near carrying capacity Examples: Sharks Elephants

Other population factors Predation Competition

Human Populations Age Structures and Human Growth

Human Population Growth Human population growth does not currently show density effects that typically characterize natural populations. In natural populations, per capita population growth rate decreases with population size, whereas global human population growth rate has a positive relationship.

Population Age Structure Differences in environmental conditions and past history may cause populations to differ in their age distributions. The future growth of a population depends on its current age distribution.

Age Structure A population’s age structure indicates the percentage of individuals at each age. The right side shows females; the left, males The x-axis is number is populations size Usually in millions The y-axis is age ranges usually 0 -4, 5 -9, 10 -14, etc…

US Dynamic Age Structure

me Ya’ll

History of Human Population Growth • The Development of Agriculture – About 10, 000 to 12, 000 years ago, the development of agriculture increased the growth rate of the human population.

What happened in the 1600 s? The Population Explosion Around 1650, improvements in hygiene, diet, and economic conditions further accelerated population growth. After World War II, the human population grew at the fastest rate in history, largely because of better sanitation and medical care in poorer countries.

Advances in Human Technology = Growth

1. What is the difference between linear growth and exponential growth as plotted on a graph? 2. Explain the graph of linear growth shown.

4. Why don’t populations of organisms grow indefinitely? 5. What is the relation ship of births to deaths in a population before the population reaches the environment’s carrying capacity? 6. What happens when the population exceeds the carrying capacity? 7. What are some limiting factors that can curb population growth?

Human population growth rate has been growing more than exponentially. Limited resources eventually will cause human population growth to slow, but global human carrying capacity is not known.