Ch 5 Population Ecology Part 1: Foundations of Environmental Science PowerPoint® Slides prepared by Jay Withgott and Heidi Marcum Copyright © 2008 Pearson Education, Inc., publishing as Benjamin Cummings

This lecture will help you understand: Population characteristics Population ecology Conservation biology

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

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

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

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

Gause’s Principle No two species can fill the same niche at the same time The weaker species will fill the smaller niche, relocate or die.

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

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

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

Population ecology 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

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

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

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

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

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

Perfect logistic curves aren’t often found

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

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

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

K-selected vs. r-selected species

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

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

Preserving biodiversity Natural parks and protected areas help preserve biodiversity Often, they are underprotected & underfunded Ecotourism brings jobs and money to developing areas

QUESTION: Review Which of the following is NOT a part of the process of natural selection? a) Organisms struggle to survive b) Organisms limit the number of young they produce c) Individuals vary in their genetic characteristics d) Some individuals are better suited to their environment than others Answer: b

QUESTION: Review Disruptive selection would result in which of the following? a) Dogs with black coats evolving whiter coats in colder areas b) Red and white flowers interbreeding, producing pink flowers c) Fish evolving bigger eyes as the water gets muddier d) A population of birds, some with thicker beaks that eat seeds and others with thinner beaks that eat insects Answer: d

QUESTION: Review Biological diversity includes all of the following, except: a) Species diversity b) Genetic diversity c) Population diversity d) Community diversity e) All of these are included in the concept of biodiversity Answer: e

QUESTION: Review Sympatric speciation would occur in .... a) One population that mates in May, and another that mates in June b) Two populations separated by the Mississippi River c) Two populations separated by a glacier d) Two populations separated by the Rocky Mountains Answer: a

QUESTION: Review Which of these species is least vulnerable to extinction? a) A species with a population size of 50 individuals b) A species distributed throughout the United States c) A species that eats only river snails d) A species that lives on mountaintops Answer: b

QUESTION: Review An ecosystem is defined as: a) The total living things on Earth b) Members of the same population that can interbreed c) Interacting species in an area d) Species and the nonliving material they interact with Answer: d

QUESTION: Viewpoints Should we care whether a species goes extinct? Yes, because all life is important and valuable Yes, because we are causing this wave of extinction, so we should fix it We should not, because it’s natural I don’t care; it really does not affect me Answer: any

QUESTION: Viewpoints Do you think humans are subject to limiting factors and, ultimately, a fixed carrying capacity? Yes, although we have raised the carrying capacity, there are limits to the number of humans the Earth can support Yes, but technology will keep raising the carrying capacity, so it’s not much of a problem No, humans are no longer constrained by environmental limits, due to our technology and ability to manipulate the environment I don’t care; it really does not affect me Answer: any

QUESTION: Interpreting Graphs and Data Which of the following graphs shows a population that will have fewer individuals in the future? Answer: d (a) (b) (c) (d)

QUESTION: Interpreting Graphs and Data Which type of distribution is a result of individuals guarding their territory? a) Random b) Uniform c) Clumped d) None of these Answer: b

QUESTION: Interpreting Graphs and Data What does this graph show? a) The effects of carrying capacity on population growth b) A population that keeps growing c) The effects of exponential growth d) The effects of increasing carrying capacity Answer: a