Chapter 8

1. Chapter 8 Understanding Populations

2. 8-1: How Populations Change Size • Describe the three main properties of a population. (slide 3 & 4) • Describe exponential population growth. (slide 6, 7, 11, 12) • Describe how the reproductive behavior of individuals can affect the growth rate of their population. (slide 6 & 7) • Explain how population sizes in nature are regulated. (slide 8)

3. What is a population? • All the members of the same species living in the same place at the same time. • “reproductive group” or “gene pool” • Population refers to the group in general and to the size of the group • Daisies in Ohio, not in Maryland • Bass in a lake in Iowa • Properties of populations: • Size • Density • dispersion

4. Size • Number of individuals in the population • 250,000 people in Kalamazoo County (2010 census) • Density • Individuals per unit of area or volume • 75 deer per square mile • Dispersion • Distribution or arrangement • Even – pine trees in rows in a forest; corn fields • Clumped – zebras in the savanna; deer herds • Random- dandelions in a field; lizards in the desert

5. Population Growth • Growth rate is calculated using change in = births – deaths population size *Also included would be immigrants to the area and emigrants from the area *Growth rate can be positive or negative numbers; with negative numbers equaling a decrease in population size

6. Growth Curves • Biotic potential = fastest rate at which a population can grow. This is also called fercundity (max number of offspring that could be produced vs fertility which is number actually produced). • Reproductive potential = max. number that a population can produce. • Earlier maturity • Larger numbers of eggs • Shorter generation time • Survival rate

7. Sea turtle lay >2000 eggs, they don’t all survive • A pair of elephants could produce 19 million descendants in 750 years….but have one at a time, gestate 20+ months, nurse 4+ years, 15 when mature, raise 1 at a time; even if live to be 100 – only have a couple kids • Bacteria and insects have very short generation times. • Average generation time for humans is 20 years

8. Limits to population growth • Resources are never unlimited or constant; they are either used up or they change. • A limited resource is something the species needs and consumes at the same rate its produced. • Leads to competition • Carrying capacity = theoretical limit to populations size in a given ecosystem. • Rabbits in Australia • Islands make good studies because of boundaries • Regulation • Density dependent – rate of death is worse when individuals are closely packed (infection in pine trees) • Density independent – rate of death is not dependent on numbers of individuals in the area; storms, crops freezing , etc.

9. 8-2: How Species Interact with Each Other • Explain the difference between niche and habitat. (slide 17-19) • Give examples of parts of a niche. (slide 17-19) • Describe the five major types of interactions between species. (slide 14 & 15) • Explain the difference between parasitism and predation. (slide 14) • Explain how symbiotic relationships may evolve.

10. 8.2: Population Dynamics • Population – group of similar individuals that are in the same place, at the same time and comprise a gene pool • Species – organisms that are similar enough to interbreed in nature and produce viable offspring. • Breed, variety, strain, subspecies, etc. • “dynamic” means in constant motion, always changing, not static.

11. Births increase population • Deaths decrease population • If births = deaths then population is steady, called “replacement rate” • If growth is exponential then population increases rapidly…. Parents have 2 kids (4) and they each have 2 kids (8), and they have 2 kids (16)….. The sum of population would go like this 2,4,8,16,32….

12. Population Growth patterns • Logistic – steady (“S”) • Exponential – increasing rapidly (“J”) • In a new situation populations have the potential to increase exponentially, but natural forces like food/resources, predators and space will eventually create a stable level when the population reaches “Carrying Capacity”

14. Symbiosis • In addition to enough food, water, oxygen, sun, space, mates and other resources – individuals have interactions with other species that impact their survival and reproductive success. • Competition (rabbit and penguins, bugs and food) • Can be direct or indirect • Predator – prey (rabbit – lynx) • Commensalism (bromeliads like orchids) • Mutualism (acacia/ants, pollinators, intestinal bacteria) • Parasitism (mosquito, lice, leech, tapeworm)

17. Resource Partitioning • In order to decrease competition some resources are allocated or partitioned to specific species • Common examples include birds that specifically live in the upper branches, lower branches, or interior of the tree so that one tree can house 3 species in their own separate zones

19. Niche • An organism’s unique role within an ecosystem is it’s NICHE; FUNCTION or job… “grazer”, “pollinator”, etc • Physical space + • Environmental factors + • Interactions • Realized Niche vs Fundamental Niche • Where you actually are vs. anywhere you could be successful • Habitat = WHERE you live

20. Humans • The human population is also subject to all of the conditions studied in ecology • Resource availability (coal, Al, transportation, Rx) • Material resources, goods and infrastructure including services • Water, air, food • Space • Waste • Pollution Disease/ immunity • Genetic impacts “Creativity” • Carrying capacity is hard to calculate due to the number of variables.