Ch 5 Evolution, Biodiversity, and 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

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This lecture will help you understand: Natural selection How evolution influences biodiversity Reasons for species extinction Ecological organization Population characteristics Population ecology Conservation biology

Ecology is studied at several levels Ecology and evolution are tightly intertwined Biosphere = the total living things on Earth and the areas they inhabit Ecosystem = communities and the nonliving material and forces they interact with Community = interacting species that live in the same area

Levels of ecological organization Population ecology = investigates the quantitative dynamics of how individuals within a species interact Community ecology = focuses on interactions among species Ecosystem ecology = studies living and nonliving components of systems to reveal patterns Nutrient and energy flows

Population Ecology Population = a group of individuals of a species that live in the same area

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

Evolution: the source of Earth’s biodiversity Biological evolution = genetic change in populations of organisms across generations May be random or directed by natural selection Natural Selection = the process by which traits that enhance survival and reproduction are passed on more frequently to future generations than those that do not

Understanding evolution is vital It alters the genetic makeup of a population It is important for understanding antibiotic and pesticide resistance, agricultural issues, production, medicines, etc. Organisms adapt to their environment and change over time

Natural selection shapes organisms In 1858, Darwin and Wallace both proposed natural selection as the mechanism of evolution Organisms face a constant struggle to survive and reproduce Organisms tend to produce more offspring than can survive Individuals of a species vary in their characteristics due to genes and the environment Some individuals are better suited to their environment and will survive and pass their genes on in their offspring

Genetic variation Adaptive Trait (Adaptation) = a trait that promotes reproductive success Mutations = accidental changes in DNA that may be passed on to the next generation Non-lethal mutations provide the genetic variation on which natural selection acts Sexual reproduction also leads to variation

Natural selection acts on genetic variation Directional selection = drives a feature in one direction Stabilizing selection = produces intermediate traits, preserving the status quo Disruptive selection = traits diverge in two or more directions If the environment changes, a trait may no longer be adaptive http://wps.pearsoncustom.com/wps/media/objects/3014/3087289/Web_Tutorials/17_A02.swf

Evidence of natural selection is everywhere It is evident in every adaptation of every organism Evident in bacteria and fruit flies in laboratories Selective breeding of animals

Artificial selection Artificial Selection = the process of selection conducted under human direction For example, artificial selection has led to the great variety of dog breeds

Evolution generates biodiversity Biological Diversity = An area’s sum total of all organisms The diversity of species Their genes Their populations Their communities Species = a population or group of populations whose members share characteristics and can freely breed with one another and produce fertile offspring Population = a group of individuals of a species that live in the same area

Speciation produces new types of organisms The process of generating new species A single species can generate multiple species Allopatric speciation = species formation due to physical separation of populations Can be separated by glaciers, rivers, mountains The main mode of species creation http://wps.pearsoncustom.com/wps/media/objects/3014/3087289/Web_Tutorials/18_A01.swf

Another type of speciation Sympatric speciation = species form from populations that become reproductively isolated within the same area Feed in different areas, mate in different seasons Hybridization between two species Mutations

Speciation results in diverse life forms Speciation generates complex patterns of diversity above the species level Phylogenetic trees (Cladograms) = Represents the history of species divergence Scientists can trace when certain traits evolved Show relationships between species

Why didn’t the Golden Toad “Adapt”?

Extinction Species generally evolve from simple to complex and small to big, but the opposite can occur, and some even disappear Extinction = the disappearance of a species from Earth Occurs when a species cannot adapt quickly enough to a changing environment Speciation and extinction affect species numbers

Extinction is a natural process Extinction is irreversible: once a species is lost, it is lost forever Humans profoundly affect rates of extinction

Some species are more vulnerable to extinction Extinction occurs when the environment changes too rapidly for natural selection to keep up Endemic species = a species only exists in a certain, specialized area Very susceptible to extinction These species usually have small populations Many other factors also cause extinction Severe weather New species Specialized species

Earth has had several mass extinctions Background extinction rate = extinction usually occurs one species at a time Mass extinction events = five events in Earth’s history that killed off massive numbers of species at once 50-95% of all species went extinct at one time Humans are causing the sixth mass extinction event Resource depletion Population growth Development

Species’ ranges can be severely restricted Some U.S. salamander species live on top of single mountains

Organismal ecology: habitat Habitat = the environment in which an organism lives Includes living and nonliving elements Scale-dependent: from square meters to miles Habitat use = each organism thrives in certain habitats, but not in others 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 developments conflict 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 live in many different places and NICHES

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 Capture, Mark and Recapture Technique

Capture, Mark and Recapture

Population characteristics Population density = the number of individuals within a population per unit area High densities make it easier to find mates, but increase competition, and vulnerability to predation Low densities make it harder to find mates, but individuals enjoy plentiful resources and space The Good and the Bad…

Population characteristics Population distribution (dispersion) = spatial arrangement of organisms within an area Random – haphazardly located individuals, with no pattern Uniform – individuals are evenly spaced due to territoriality Clumped – arranged according to availability of resources Most common in nature

Population characteristics Sex ratio = proportion of males to females In monogamous species, a 50/50 sex ratio maximizes population growth Age Structure = the relative numbers of organisms of each age within a population Age structure diagrams (pyramids) = show the age structure of populations

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

Is it good or bad for a large number of individuals in a population to die at a young age? It depends…. On What?

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

Exponential population growth Steady growth rates cause exponential population growth Something 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 and ideal conditions

Limiting factors restrain growth Limiting factors = physical, chemical and biological characteristics that restrain population growth Water, space, food, predators, and disease 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 changes 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 risk of predation and competition for mates occurs with increased density Density-independent factors = limiting factors whose influence is not affected by population density Events such as floods, fires, and landslides

Biotic potential and reproductive strategies vary Biotic potential = the ability of an organism to produce offspring K-selected species = animals with long gestation periods and few offspring Have a low biotic potential Stabilize at or near carrying capacity Good competitors r-selected species = animals which reproduce quickly Have a high biotic potential Little parental care

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 source of resources Human population growth pressures biodiversity

Preserving biodiversity Natural parks and protected areas help preserve biodiversity Often, they are 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: 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

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