© 2011 Pearson Education, Inc. Population Ecology Ecological organization Population characteristics Population ecology

© 2011 Pearson Education, Inc. Evolution generates biodiversity Species = a population or group of populations -Whose members share characteristics -They can breed with one another and produce fertile offspring Population = a group of individuals of a species that live in the same area

© 2011 Pearson Education, Inc. Genetic variation Adaptation = the process where, over time, characteristics (traits) that lead to better reproductive success -Become more prevalent in the population Adaptive trait (adaptation) = a trait that promotes reproductive success

© 2011 Pearson Education, Inc. Ecology is studied at several levels Ecology and evolution are tightly intertwined Biosphere = the total living things on Earth -And the areas they inhabit Community = interacting species living in the same area Ecosystem = communities and the nonliving material and forces they interact with

© 2011 Pearson Education, Inc. Each organism has habitat needs Habitat = the environment where an organism lives -It includes living and nonliving elements

© 2011 Pearson Education, Inc. A specialized frog Epiphytes grow on trees for support -Obtaining water from the air -They collect pools of rainwater and pockets of leaf litter -Frogs lay their eggs in these rainwater pools

© 2011 Pearson Education, Inc. Organismal ecology: niche Niche = an organism’s use of resources -Along with its functional role in a community -Habitat use, food selection, role in energy and nutrient flow, interactions with other individuals Specialists = have narrow niches and specific needs -Extremely good at what they do -But vulnerable when conditions change Generalists = species with broad niches -They use a wide array of habitats and resources -They can live in many different places

© 2011 Pearson Education, Inc. Population characteristics All populations show characteristics that help scientists predict their future dynamics Population size = the number of individual organisms present at a given time -Numbers can increase, decrease, cycle or remain the same

© 2011 Pearson Education, Inc. Population characteristics Population density = the number of individuals in a population per unit area Large organisms usually have low densities -They need many resources and a large area to survive High densities make it easier to find mates -But increase competition and vulnerability to predation -Increased transmission of diseases Low densities make it harder to find mates -But individuals enjoy plentiful resources and space

© 2011 Pearson Education, Inc. Sex ratio = proportion of males to females -In monogamous species, a 1:1 sex ratio maximizes population growth Age distribution (structure) = the relative numbers of organisms of each age in a population -Age structure diagrams (pyramids) = show the age structure of populations In species that continue growing as they age -Older individuals reproduce more (i.e. a tree) -Experience makes older individuals better breeders Population characteristics

© 2011 Pearson Education, Inc. Four factors of population change Natality = births within the population Mortality = deaths within the population Immigration = arrival of individuals from outside the population Emigration = departure of individuals from the population Births and immigration add individuals -Deaths and emigration remove individuals Crude birth (death) rates: number of births (deaths) per 1000 individuals per year

© 2011 Pearson Education, Inc. Population growth rate Natural rate of population growth = (Crude birth rate) – (crude death rate) -Population change due to internal factors Population growth rate = (Crude birth rate + immigration rate) – (Crude death rate + emigration rate) -Net changes in a population’s size/1000/year Growth rate as a percent = -Population growth rate * 100% -Populations of different sizes can be compared

© 2011 Pearson Education, Inc. Exponential population growth Exponential growth -A population increases by a fixed percent -Graphed as a J-shaped curve Exponential growth cannot be sustained indefinitely It occurs in nature with a: -Small population -Low competition -Ideal conditions

© 2011 Pearson Education, Inc. Limiting factors restrain population growth Limiting factors = physical, chemical and biological attributes of the environment -They restrain population growth Environmental resistance = all limiting factors taken together -Stabilizes the population size -Space, food, water, mates, shelter, suitable breeding sites, temperature, disease, predators -Aquatic systems: salinity, sunlight, temperature, etc.

© 2011 Pearson Education, Inc. Carrying capacity Carrying capacity = the maximum population size of a species that its environment can sustain Limiting factors slow and stop exponential growth -An S-shaped logistic growth curve Many factors contribute to environmental resistance and influence a population’s growth rate and carrying capacity

© 2011 Pearson Education, Inc. Perfect logistic curves aren’t often found

© 2011 Pearson Education, Inc. Carrying capacities can change Environments are complex and ever-changing -Changing carrying capacities Humans lower environmental resistance for themselves -Increasing our carrying capacity -Technologies overcome limiting factors By increasing carrying capacity for humans -We have reduced the carrying capacity for countless other organisms -Calling into question our own long-term survival