Unit III: Populations Chapter 8: Understanding Populations 8-1 How Populations Change in Size Population: all members of a species living in the same place at the same time (ex. All the water lilies in a pond). *Specific species, specific location.* Population: all members of a species living in the same place at the same time (ex. All the water lilies in a pond). *Specific species, specific location.*

3 Key Properties of Populations: 1. Population Size: # of individuals in a population Very small populations are likely to become extinct Very small populations are likely to become extinct * Inbreeding (breeding w/ relatives) is common in small populations * Inbreeding (breeding w/ relatives) is common in small populations –unfavorable recessive traits are more likely to be homozygous and therefore expressed. –Reduced variability limits the population’s ability to adapt. 2. Population Density: # of individuals found in a given area Widely spaced populations may rarely or never encounter one another, making reproduction rare Widely spaced populations may rarely or never encounter one another, making reproduction rare 3. Population Dispersion: the way the individuals of the population are arranged Randomly spaced: determined by chance Randomly spaced: determined by chance evenly spaced: regular intervals evenly spaced: regular intervals clumped: bunched together (*most common type of distribution in nature) clumped: bunched together (*most common type of distribution in nature)

RandomEvenClumped

Growth Rate: Change in pop. size = birth rate – death rate Change in pop. size = birth rate – death rate Can be positive, negative, or zero Can be positive, negative, or zero

Reproductive Potential: the maximum # of offspring each member of the population can produce Biotic Potential: the fastest rate at which a species population can grow (limited by reproductive potential) Biotic Potential: the fastest rate at which a species population can grow (limited by reproductive potential) Reproductive Potential Increased by: Reproductive Potential Increased by: Producing more offspring at a time Producing more offspring at a time Reproducing more often Reproducing more often Reproducing earlier in life (has greatest effect) Reproducing earlier in life (has greatest effect) –Shortens generation time: avg. time it takes a member of the population to reach the age when it reproduces.  Small organisms = short generation times (bacteria & insects = few hours-few days)  Large organisms – long generation time (humans = about 20 years) Who has a higher reproductive potential – humans or insects? Who has a higher reproductive potential – humans or insects?

Exponential Growth: when populations grow faster and faster Occurs in nature when: plenty of food and space, no competition or predators Occurs in nature when: plenty of food and space, no competition or predators Forms a J-shaped curve when graphed Forms a J-shaped curve when graphed constant growth rate, population grows quickly as the size of the population increases constant growth rate, population grows quickly as the size of the population increases ex. Human Population Growth ex. Human Population Growth

Carrying Capacity: maximum population size an ecosystem can support Eventually as the population grows the growth rate falls (birth rates decline and death rates rise) Eventually as the population grows the growth rate falls (birth rates decline and death rates rise) Why? Competition for food, shelter, mating sites, and other resources, and the accumulation of toxic wastes tends to increase as a population approaches its carrying capacity. Why? Competition for food, shelter, mating sites, and other resources, and the accumulation of toxic wastes tends to increase as a population approaches its carrying capacity. Forms an S-shaped curve when graphed. Forms an S-shaped curve when graphed. a.k.a. equilibrium a.k.a. equilibrium

Limiting resource / limiting factor: resources that limit the size of a population (mainly abiotic factors) Competition for limiting resources is often indirect (ex. social dominance or territory) Competition for limiting resources is often indirect (ex. social dominance or territory) –Territory: an area defended by 1 or more individuals against other individuals (of value for space, shelter, food, or breeding sites)

2 Types of Population Regulation 1. Density-Dependent Factors: cause of death occurs more quickly in a crowded population than in a sparse population cause of death occurs more quickly in a crowded population than in a sparse population the effect on the size of the population DEPENDS upon the density or size of the population (usually biotic factors ex. Disease, parasites, competition, etc) the effect on the size of the population DEPENDS upon the density or size of the population (usually biotic factors ex. Disease, parasites, competition, etc) 2. Density-Independent Factors: a certain portion of a population may die regardless of the population’s density a certain portion of a population may die regardless of the population’s density unrelated to population size. affect everyone in the population regardless of population size (usually abiotic factors ex. Weather, climate, natural disasters, etc.) unrelated to population size. affect everyone in the population regardless of population size (usually abiotic factors ex. Weather, climate, natural disasters, etc.)

8-2 How Species Interact with Each Other Niche: unique roll of a species within an ecosystem Includes: Includes: –Physical home, environmental factors necessary for the species’ survival –All of the species’ interactions w/ other organisms –(where it lives, what it eats, when it reproduces, etc.) Niche vs. Habitat Habitat = organism’s location Habitat = organism’s location Niche = pattern of use of its habitat Niche = pattern of use of its habitat

Competition – common use of scarce resources Occurs within & between species Occurs within & between species Happens when niches overlap Happens when niches overlap Indirect Competition – 2 species don’t come in direct contact w/ each other (ex. 1 insect species feeds on a plant during the day, another species at night) Indirect Competition – 2 species don’t come in direct contact w/ each other (ex. 1 insect species feeds on a plant during the day, another species at night)

Adaptations to Competition Avoiding competition is an advantageous adaptation. Avoiding competition is an advantageous adaptation. Niche Restriction – each species uses less of the niche than they are capable of using Niche Restriction – each species uses less of the niche than they are capable of using –Fundamental Niche: total niche an organism could occupy w/in an ecosystem - entire range of conditions it can tolerate –Realized Niche: niche a species actually occupies (it doesn’t occupy the entire fundamental niche due to competition)

Time To Draw Some Happy Little Trees…. Fundamental NiceFundamental NiceRealized Niche Species ASpecies BSpecies A & B

Ecological Relationships Competition Species A =  - Species A =  - Species B =  - Species B =  - Example: Birds competing for seed at a feeder. Example: Birds competing for seed at a feeder. Description:2 Species use the same resources Description:2 Species use the same resources

Predation Species A = + Species A = + Species B =  - Species B =  - Example: snakes & mice Example: snakes & mice Description: Predator eats and kills the prey. Description: Predator eats and kills the prey.

Parasitism Species A = + Species A = + Species B =  - Species B =  - Example: tick & dog ; tapeworm & human Example: tick & dog ; tapeworm & human Description: Parasite lives in or on the host and feeds on the host. Description: Parasite lives in or on the host and feeds on the host.

Mutualism Species A = + Species A = + Species B = + Species B = + Example: Flowering Plant & Honey Bee Example: Flowering Plant & Honey Bee –Acacia Trees & Ants Description: Each species helps the other (both species benefit) Description: Each species helps the other (both species benefit)

Commensalism Species A = + Species A = + Species B = 0 ? Species B = 0 ? Example: Shark & Remora Example: Shark & Remora –Birds nesting in trees Description: Species A benefits, species B is unaffected. Description: Species A benefits, species B is unaffected.

Symbiosis: “living together” – 2 organisms living in close association w/ each other Includes: Parasitism, Mutualism, & Commensalism Includes: Parasitism, Mutualism, & Commensalism Often results in coevolution (both species evolve in response to one another – ex. many flowers match feeding habits of their pollinators Often results in coevolution (both species evolve in response to one another – ex. many flowers match feeding habits of their pollinators