Unit 1 The Biosphere

PopulationsInteractions

3 Properties of Populations

• Population Size• Population Density• Population Dispersion

Population Size

• Population-groups of organisms that belong to the same species and live in a particular area at one time

• Population size-number of individuals a population has

• Sometimes there are too many to count so a sampling is used.

• Scientists count a number of organisms in a certain area and multiply the area.

Population Density

• Population density-measures how crowded a population is

• The number is always expressed as the number of individuals per unit of area or volume

• Some areas are densely populated and others are sparsely populated

Population Dispersion• Dispersion is the spatial distribution

of individuals within a population.• There are three types of dispersion.• Clumped dispersion occurs because

resources and living space is clumped or because of behavior, herding

• Even dispersion is the result of social behavior and organisms stay as far away from each other as possible

• Random dispersion results from wind distribution of seeds so plants usually have a random dispersal

Types of Dispersion

Population Dynamics• All populations are dynamic, meaning

they change in size and composition over time.

• Birth rate-number of births over time• Death rate (mortality rate)-number of

deaths over time• Life expectancy- how long on average

an individual is expected to live

Age Structure

• Age structure-distribution of individuals among different ages in a population

• Different countries have different age structures.

• We can use graphs to compare age structure.

Population Growth Rate

• Growth rate- the amount by which a population’s size changes over time

• Immigration-individuals moving into a population

• Emigration-individuals moving out of a population

Exponential Growth Model

• Exponential Model- population increases rapidly after only a few generations; the larger the population gets, the faster it grows

• Limiting factor-a factor that restrains or stops the growth of a population

• Limiting factors are available resources, space, waste accumulation, population density

Logistic Growth Model

• Logistic model-builds on the exponential model but adds the limiting factors.

• Carrying capacity (K)- the number of individuals the environment can support over a long period of time

• Once carrying capacity is reached, the population remains constant

Population Regulation

• Density-independent factors-weather, flood, fires; these reduce the population regardless of size

• Density-dependent factors- food, nesting sites, illness; these occur as a result of population size

Perils of small populations- Inbreeding

• The rapidly growing human population has caused extreme reductions in the populations of some other species and subspecies.

• Fewer than 200 Siberian tigers remain in the wild due to over hunting and habitat destruction

• The California condor is down to 9 individuals.

• Fewer individuals means inbreeding or mating with relatives.

• This mean the babies will be more likely to have defects or diseases.

Predation

•Predator-captures, kills and consumes another individual

•Prey-is captured and consumed for food

Predators, Prey and Natural Selection

• A predator’s survival depends on its ability to capture food, but a prey’s survival depends on its ability to avoid being captured.

Mimicry• Deception is important in

antipredator defenses.• In a defense called mimicry, a

harmless species resembles a poisonous or distasteful species.

• The harmless mimic is protected because it is often mistaken to be its dangerous look-alike

MimicryMonarch

Viceroy

National Geographic’s Collection of Mimicry and Camouflage

Plant-Herbivore Interactions

• Animals that eat plants are called herbivores.

• Through natural selection, plants have evolved adaptations that protect them from being eaten.

• Physical defenses, such as sharp thorns, spines, sticky hairs, and tough leaves, can make a plant more difficult to eat.

Plant-Herbivore Interactions

• Plants have also evolved a range of chemical defenses.

• They synthesize chemicals from products of their metabolism, called secondary compounds, that are poisonous, irritating, or bad tasting.

• Examples are the tobacco plant and poison ivy and poison oak.

• Many medicines are derived from secondary compounds.

Secondary Compounds

Purple Coneflower or Echincaea.

Immune system

Willow Tree

aspirin

Parasitism

• Parasitism- a species interaction that resembles predation in that one individual is harmed while the other benefits

• Parasite- feeds on another individual, harming it

• Host-fed upon by another organism• Ectoparasites-external, ticks, fleas, lice• Endoparasites-internal, worms, protists

Ectoparasites

Endoparasites

Competition• Competition results from niche overlap.• Competition is the use of the same

limited resource by two or more species.

• Competitive exclusion is when one species is eliminated from a community due to competition.

• One species uses a resource more efficiently and has a reproductive advantage over the other.

• Competition is the most intense between similar species using the same resources.

Mutualism and Commensalism

• Mutualism- a cooperative relationship in which both partners benefit

• Some mutualistic relationships are so close that neither partner could live without the other.

• Pollination is a major mutualistic relationship that benefits the world.

Mutualism and Commensalism

• Commensalism- a relationship between organisms in which one organism benefits and one organism is unaffected.

• One example is birds eating insects and lizards that are flushed out by buffalo.

• The buffalo is not harmed and does not benefit but the birds clearly benefit from the buffalo.

Mutualism

CommensalismThese are mainly commensalism but could change to mutualism if the situation changes.

Commensalism

Mutualism

commensalism

Parasitism

Predation

Parasitism

mutualism

mutualism