Chapter 4: Population Biology

Population group of organisms, all of the same species, that live in a specific area

How fast do populations grow? Not linear growth – so it is not a straight line Graph- starts to increase slowly, then resembles a J-shaped curve Initial increase slow, b/c # of organisms that reproduce is small Increases b/c the total # of individuals that can reproduce has increased

Is Growth Limited? J-shaped growth curve illustrates exponential population growth Exponential Growth – means that as a population get larger, it also grows at a faster rate

What Can Limit Growth? Population growth does have limits Limiting Factors – food, disease, predators, or lack of space will Cause population growth to SLOW Under these conditions the population may stabilize in a S-shape growth curve

Carrying Capacity the number of organisms of one species that an environment can support indefinitely  Developing population – more births than deaths and the population increases until the carrying capacity is reached or passed When a population overshoots the carrying capacity, limiting factors come into affect Deaths begin to exceed births and the population falls below the carrying capacity

Reproduction Patterns Life-History Pattern- organisms reproduction pattern Slow life-history pattern – slow rate of reproduction and produce relatively few offspring   Ex. Elephant Fast life-history pattern – reproduce rapidly and produce many offspring in a short period of time Ex. Mosquito

Rapid Life- History Patterns Common among organisms in changeable or unpredictable environments Organisms have: Small body size Mature rapidly Reproduce early Short life span reproduction rises rapidly then decline when environment becomes unsuitable population survives and will reproduce again when the environment is favorable

Slow Life- History Patterns large species that live in more stable environments Elephants, Bears, Whales, Humans, and plants (trees) reproduce and mature slowly long-lived maintain population sizes at or near carrying capacity

Density Factors and Population Growth   3 Patterns of Dispersal: 1. Random 2. Clumped 3. Uniform

Density-Dependent Factors disease competition predators parasites food

increasing affect as the population increases Example- corn fields Crops grow close together Disease can spread rapidly and kill off the whole crop

Density-Independent Factors can effect most populations regardless of their density Most are abiotic factors   Volcanic eruptions Temperature Storms Floods Drought Chemical Pesticides Major habitat destruction Usually affect smaller organisms more Example – Mosquitoes – severe winters kill the adults of most species

Population Size limited by abiotic and biotic factors controlled by various interactions among organisms that share a community Predation – can effect population size in minor and major ways

Locusts eat acres of lettuce on a farm Brown snake introduced into Guam, there were no native predators, and it preyed freely on native birds – drastic effect on the population size

predator- prey relationships are known to experience cycles or changes in their numbers over periods of time prey population increases and there is more food for the predator, so the predator population increases predator population increase and predation increase, therefore – the prey population declines. With less food, the predator population decrease. Cycle starts again

Competition within a Population density dependent factor few individuals compete for resources, usually no problems When population increase and the demand exceeds the supply, the population size decreases

Crowding and Stress populations become crowded, individuals exhibit stress stress symptoms Aggression decrease in parental care decreased fertility decreased resistance to disease all have negative effects on a population

Human Population Demography – study of human population size density and distribution movement Birth and death rates

Human Population Growth Humans change their environment Developed methods for producing more food infant mortality rate decreased clean water All enable people to live longer and produce more offspring Population Grows

Calculating Growth Rate Birthrate – number of live births per 1000 population in a given year Death rate – number of deaths per 1000 population in a given year Immigration – movement of individuals into a population Emigration – movement of individuals out of a population

Calculate a population’s growth rate by (Birthrate + Immigration Rate) – (Death rate + Emigration Rate) = Population Growth Rate PGR = (B + I) – (D + E) Immigration and emigration are not always accurate use:   PGR = Birthrate – Death rate

Positive Growth Rate unless the growth rate becomes negative the population continues to grow, just slower Doubling Time time needed for a population to double in size Age Structure refers to the portions of the population that are in the different age levels