Copyright © 2008 Pearson Education, Inc., publishing as Benjamin Cummings WARM UP What does the capital letter K represent in ecology? What does it mean to be a K-selected species?

Copyright © 2008 Pearson Education, Inc., publishing as Benjamin Cummings POPULATION ECOLOGY

Copyright © 2008 Pearson Education, Inc., publishing as Benjamin Cummings Ecology is studied at several levels Ecology and evolution are tightly intertwined Biosphere = all living things on Earth and the areas they inhabit Ecosystem = communities and the nonliving (abiotic) material and forces they interact with Community = interacting species that live in the same area

Copyright © 2008 Pearson Education, Inc., publishing as Benjamin Cummings Levels of ecology science Population ecology = investigates the quantitative dynamics of how individuals within a species interact Community ecology = focuses on interactions among species (one-on-one to interrelationships among communities) Ecosystem ecology = studies living and nonliving components of systems to reveal patterns -nutrient and energy flow

Copyright © 2008 Pearson Education, Inc., publishing as Benjamin Cummings Organismal ecology: habitat Habitat = the environment in which an organism lives -includes living and nonliving elements -scale-dependent: from square meters to square km Habitat use = each organism thrives in certain habitats, but not in others (non-random patterns) Habitat selection = the process by which organisms actively select habitats in which to live -availability and quality of habitat are crucial to an organism’s well-being -human development conflicts with this process

Copyright © 2008 Pearson Education, Inc., publishing as Benjamin Cummings Organismal ecology: niche Niche = an organism’s use of resources and its functional role in a community -habitat use, food selection, role in energy and nutrient flow -interactions with other individuals Specialists = species with narrow niches and very specific requirements -extremely good at what they do, but vulnerable to change Generalists = species with broad niches that can use a wide array of habitats and resources -able to weather variable conditions, may not thrive

Copyright © 2008 Pearson Education, Inc., publishing as Benjamin Cummings Gause’s Principle (aka Competitive Exclusion Principle) No two species can fill the same niche at the same time The weaker species will fill the smaller niche, relocate or become extinct.

Copyright © 2008 Pearson Education, Inc., publishing as Benjamin Cummings Population ecology All populations show characteristics that help scientists predict their future dynamics Understanding human population dynamics is central to environmental science Population size = the number of individual organisms present at a given time -numbers can increase, decrease, cycle, or remain the same

Copyright © 2008 Pearson Education, Inc., publishing as Benjamin Cummings Population ecology Population density = the number of individuals within a population per unit area -high densities make it easier to find mates, but increases competition, and vulnerability to predation & disease -low densities make it harder to find mates, but individuals benefit from more resources and space

Copyright © 2008 Pearson Education, Inc., publishing as Benjamin Cummings Population ecology Population distribution (dispersion) = spatial arrangement of organisms within an area -Random – individuals located haphazardly, with no pattern -Uniform – individuals are evenly spaced, can be due to territoriality -Clumped – arranged according to availability of resources needed to survive -most common in nature

Copyright © 2008 Pearson Education, Inc., publishing as Benjamin Cummings Sex ratio = proportion of males to females -in monogamous species, a 50/50 sex ratio maximizes population growth Age structure (distribution) = the relative numbers of organisms of each age within a population -Age structure diagrams (pyramids) = show the age structure of populations Population ecology

Copyright © 2008 Pearson Education, Inc., publishing as Benjamin Cummings Birth and death rates Crude birth/death rates = rates per 1000 individuals Survivorship curves = the likelihood of death varies with age -Type I: More deaths at older ages -Type II: Equal number of deaths at all ages -Type III: More deaths at young ages

Copyright © 2008 Pearson Education, Inc., publishing as Benjamin Cummings 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 Growth rate formula = -(Crude birth rate + immigration rate) - (Crude death rate + emigration rate) = Growth rate -per 1000 individuals per year -expressed in % - better able to compare populations

Copyright © 2008 Pearson Education, Inc., publishing as Benjamin Cummings Exponential population growth Steady growth rates cause exponential population growth -increases by a fixed percent -Graphed as a J-shaped curve Exponential growth cannot be sustained indefinitely -occurs in nature with a small population and ideal conditions -usually when introduced to a new environment

Copyright © 2008 Pearson Education, Inc., publishing as Benjamin Cummings Limiting factors restrain population growth Limiting factors = physical, chemical and biological characteristics that restrain population growth -water, space, food, mates, shelter, breeding sites, temperature, predators, and disease -interaction of these factors determines carrying capacity -may be determined by experiment Environmental resistance = All limiting factors taken together

Copyright © 2008 Pearson Education, Inc., publishing as Benjamin Cummings Carrying capacity Carrying capacity = the maximum population size of a species that its environment can sustain -An S-shaped logistic growth curve -Limiting factors slow and stop exponential growth Carrying capacity can vary Humans have raised their carrying capacity by decreasing the carrying capacity for other species

Copyright © 2008 Pearson Education, Inc., publishing as Benjamin Cummings Perfect logistic curves aren’t often found

Copyright © 2008 Pearson Education, Inc., publishing as Benjamin Cummings Population density affects limiting factors Density-dependent factors = limiting factors whose influence is affected by population density -increased chance of finding mates, but risk of predation and competition for mates occurs with increased density Density-independent factors = limiting factors whose influence is not affected by population density -temperature extremes & catastrophic events such as floods, fires, and landslides

Copyright © 2008 Pearson Education, Inc., publishing as Benjamin Cummings Biotic potential and reproductive strategies vary Biotic potential = the ability of an organism to produce offspring Interaction between biotic potential and environmental resistance helps determine the fate of the population

Copyright © 2008 Pearson Education, Inc., publishing as Benjamin Cummings Biotic potential and reproductive strategies vary K-selected species = animals with long gestation periods and few offspring -Have a low biotic potential -Invest in offspring -Stabilize at or near carrying capacity (K) -Good competitors -Regulated by density-dependent factors r-selected species = animals which reproduce quickly & in quantity -Have a high biotic potential -Produce as many off spring as possible/little parental care -At or below carrying capacity -Regulated by density-independent factors

Copyright © 2008 Pearson Education, Inc., publishing as Benjamin Cummings K-selected vs. r-selected species

Copyright © 2008 Pearson Education, Inc., publishing as Benjamin Cummings Striking gold in Costa Rica Golden toads were discovered in 1964, in Monteverde, Costa Rica The mountainous cloud forest has a perfect climate for amphibians Unfortunately, they became extinct within 25 years -Due to global warming’s drying effect on the forest

Copyright © 2008 Pearson Education, Inc., publishing as Benjamin Cummings Population changes affect communities As population in one species declines, other species may appear Human development now displaces other species and threatens biodiversity -As Monteverde dried out, species from lower, drier habitats appeared -But, species from the cloud-forest habitats disappeared

Copyright © 2008 Pearson Education, Inc., publishing as Benjamin Cummings Challenges to protecting biodiversity Social and economic factors affect species and communities -Nature is viewed as an obstacle to development -Nature is viewed as only a natural resource -Human population growth pressures biodiversity

Copyright © 2008 Pearson Education, Inc., publishing as Benjamin Cummings Preserving biodiversity Natural parks and protected areas help preserve biodiversity -Often, they are underprotected & underfunded -Ecotourism brings jobs and money to developing areas