Copyright © 2004 Pearson Education, Inc., publishing as Benjamin Cummings Fundamentals of Anatomy &…
Evolution, Biodiversity, and Population EcologyText+Ch+3...Copyright © 2006 Pearson Education,...
Transcript of Evolution, Biodiversity, and Population EcologyText+Ch+3...Copyright © 2006 Pearson Education,...
Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings
PowerPoint® Slides prepared by Jay Withgott and Heidi Marcum
PowerPoint® Slides prepared by Jay Withgott and Heidi Marcum
Ch 5Evolution, Biodiversity, and Population Ecology
Part 1: Foundations of Environmental Science
Copyright © 2008 Pearson Education, Inc., publishing as Benjamin Cummings
Copyright © 2008 Pearson Education, Inc., publishing as Benjamin Cummings
This lecture will help you understand:
• Natural selection • How evolution influences
biodiversity • Reasons for species extinction • Ecological organization • Population characteristics • Population ecology • Conservation biology
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Striking gold in Costa Rica
• Golden toads were discovered in 1964, in Monteverde, Chile
• 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
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Early Earth was a very different place Theory- dispersed bits of material whirling through space around our sun were drawn together by gravity
• 4.5 billion years ago, Earth was a hostile place - Severe volcanic and tectonic activity - Intense ultraviolet energy from the sun - No oxygen existed in the atmosphere, until photosynthesis
developed in microbes - No life existed
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Several hypotheses explain life’s origin
• Primordial soup (the heterotrophic hypothesis) - life originated from a “primordial soup” of simple inorganic chemicals in the oceans - First life forms used organic compounds for energy
• “Seeds” from space (the panspermia hypothesis) - microbes from space traveled on meteorites to Earth
• Life from the depths (the chemoautotrophic hypothesis) - life originated in deep-sea hydrothermal vents, with abundant sulfur - First organisms were chemoautrotrophs
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The fossil record teaches about life’s history
• Single-celled bacteria occurred on Earth 3 billion years ago
• Fossil - an imprint in stone of a dead organism
• Fossil record - gives information about the history of past life
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Present-day organisms help decipher history• Biologists use present-day
organisms to get information about evolution
• Archea - single-celled prokaryotes very different from bacteria
• The tree of life now consists of 3 prongs: bacteria, archaea, eukaryotes
• Prokaryote- a typically unicellular organism that lacks organelles and nucleus
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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
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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
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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
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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
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Natural selection acts on genetic variation
• Directional selection - drives a feature in one direction (a-thick shell protects snail)
• Stabilizing selection - produces intermediate traits, preserving the status quo (b-preserves extra resources for feeding and reproduction an favors an int. shell)
• Disruptive selection - traits diverge in two or more directions (c- two traits are favored. Thin shells conserve resources and out reproduce and thick shells are well protected)
If the environment changes, a trait may no longer be adaptive
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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
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Natural selection
• Selective breeding has produced tremendous diversity among organisms
• Adaptive radiation- burst of species formation due to natural selection
Statistics 1.5 to 1.8 million species have been discovered Estimated 100 million species mat exist
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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, and
agricultural crops
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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
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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 over some geographic distance
• DNA mutation arises in the isolated population - Can be separated by glaciers, rivers,
mountains, migration - The main mode of species creation
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Genetic Drift occurs when changes in the frequency of a gene in a population are due not to mutation, selection or migration but simply to chance
Founder Effect (allopatric) - occurs when a small number of individuals are isolated from a larger population - They may have a smaller genetic variation than the original species Both genetic drift and founder effect may not be better adapted to their environment
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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
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The fossil record shows that…
• Earlier organisms evolved into later ones • The vast majority of species are extinct • Numbers of species increase over time • Earlier organisms were smaller and simpler • Several mass extinctions have occurred • Large, complex organisms occurred 600 million years
ago - Plants, animals, fungi
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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
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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
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Extinction is a natural process
• Extinction is irreversible: once a species is lost, it is lost forever
• Humans profoundly affect rates of extinction
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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 (golden toad to the Monteverde cloud forest) - Very susceptible to extinction - These species usually have small populations
• Many other factors also cause extinction - Severe weather - New species - Specialized species
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Earth has had several mass extinctions
• Background extinction rate –the average rate of extinction that occurred before the appearance of humans
• Fossil record indicates that for both bird and mammals one species in the world typically becomes extinct every 500-1000 years or
• One to five species per million species on earth extinction usually occurs one species at a time
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Extinction
• Mass extinction events – a catastrophic widespread event where large groups of species are wiped out in a geological period lasting up to 5 million years
• five events in Earth’s history that killed off massive numbers of species at once (20-60 million years apart during the past 500 million years)
• 250 million years ago, 50-95% of all species went extinct at one time
• Humans are causing the sixth mass extinction event - Resource depletion - Population growth - Development
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Causes of Extinction
• Risk- the chance that a species of population will become extinct owing to one of these causes
1- Population Risk- random variations in population rates (in birth rates and death rates) can cause a species low in abundance to become extinct (butterfly in Colorado mountains only lay their eggs in the buds of a lupine tree. Their was a late snow killing all the buds)
2- Environmental Risk- changes in the environment that occur. This includes variations in the physical and biological environment
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Causes of Extinction – cont.
3- Natural Catastrophe- sudden changes in the environment that is not a result of human activities (volcano, earthquake, flood)
4- Genetic Risk- changes in genetic characteristics, not caused by external environmental changes (species lacks variety and may be vulnerable)
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Species’ ranges can be severely restricted
Some U.S. salamander species live on top of single mountains
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Endangered Species- Red List• The International Union for Conservation of Nature (IUCN) is
the world's main authority on the conservation status of species. A series of Regional Red Lists are produced by countries or organizations, which assess the risk of extinction to species
• The percentage of species in several groups which are listed as red critically endangered, orange endangered, or yellow vulnerable on the 2007 IUCN Red List
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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
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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
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Organismal ecology: habitat
• Habitat - the environment in which an organism lives - Includes living and nonliving elements - Scale-dependent: from square meters to miles - each organism thrives in certain habitats, but not in others (habitat use)
• 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
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Organismal ecology: niche
• Niche - an organism’s use of resources and its functional role in a community - total way of life or role of a species in an ecosystem - 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
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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
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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 Population dynamics – the study of how the characteristics of the population change in
response to changes in the environmental conditions
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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
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• 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
Population characteristics
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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
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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
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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
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Limiting factors restrain growthIntrinsic rate of increase (r) is the rate at which the population of a
species would grow if it had unlimited resources - Reproduce early in life - Have short generation times - can reproduce many times and have many offspring
• Limiting factors - physical, chemical and biological characteristics that restrain population growth - Water, space, food, predators, and disease
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Carrying capacity
• Carrying capacity (K)- 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
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Perfect logistic curves aren’t often found
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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
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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
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K-selected vs. r-selected species
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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
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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