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Introduction. Evolution and ecology are two key concepts Evolution : Changes that occur in organisms’ traits over time Ecology : How organisms live in their environment The great diversity of life on earth is the result of evolution
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Introduction • Evolution and ecology are two key concepts • Evolution: Changes that occur in organisms’ traits over time • Ecology: How organisms live in their environment • The great diversity of life on earth is the result of evolution • And evolution can be said to be the consequence of ecology over time
Fig. 2.1 Charles Darwin (1809-1882) 2.1 Darwin’s Voyage on HMS Beagle • In 1831, Charles Darwin took on the role of naturalist of the ship HMS Beagle • The Beagle set sail on a five-year navigational trip around the world
Fig. 2.3 2.1 Darwin’s Voyage on HMS Beagle • Most of the time was spent around South America
2.1 Darwin’s Voyage on HMS Beagle • Darwin studied a wide variety of plants and animals across the globe • Particularly on the Galapagos Islands • In 1859, he published his book On the Origin of Species • In it he proposed that evolution occurs through natural selection
2.2 Darwin’s Evidence • At first, Darwin was fully convinced that species were immutable • However, his observations eventually convinced him that evolution took place • Fossils of extinct species resembled living species in the same area • Galapagos finches differed slightly in appearance but resembled those on the S. American mainland
Fig. 2.5 Four Galapagos finches and what they eat • They differed mainly in beaks and feeding habitats • In all Darwin observed 14 different finch species He believed it was “descent with modification” from a common ancestor Or evolution
Fig. 2.6 2.3 The Theory of Natural Selection • Darwin was influenced by Thomas Malthus’s Essay on the Principle of Population (1798) • Populations increase geometrically, while food supply increases only arithmetically Thus, food supply will limit population growth
2.3 The Theory of Natural Selection • Darwin was also familiar with variation in domesticated animals • Breeders use artificial selection to produce animals/plants with particular traits • Darwin proposed that such trait selection could also occur in nature • A process he termed natural selection
2.3 The Theory of Natural Selection • Darwin drafted a preliminary transcript in 1842 • However, he shelved it for 16 years • Probably because of its controversial nature • Alfred Russel Wallace (1823-1913) independently developed a similar theory • Correspondence between the two spurred Darwin to publish his theory in 1859
Fig. 2.8 Darwin greets his monkey ancestor 2.3 The Theory of Natural Selection • Darwin’s Origin of Species was disturbing to many • It suggested that humans and apes have a common ancestor • Darwin presented this argument directly in a later book, The Descent of Man
2.4 The Beaks of Darwin’s Finches • Darwin collected 31 finch species from the Galapagos Islands in 1835 • Ornithologist John Gould determined that these finches were a closely-related group • They differed only in their bills • Darwin observed a correlation between the beaks and the food source of the birds • He concluded that the beaks had been shaped by evolution
Fig. 2.10 A diversity of finches on a single island 2.4 The Beaks of Darwin’s Finches
2.4 The Beaks of Darwin’s Finches • In 1938, David Lack set out to test Darwin’s hypothesis • Lack’s five-month observation seemed to contradict Darwin’s proposal • Lack found many different species of finch feeding together on the same seeds • So was Darwin wrong or is there something else going on?
2.4 The Beaks of Darwin’s Finches • In 1973, Peter and Rosemary Grant embarked on a study of the medium ground finch • Geospiza fortis feeds preferentially on small tender seeds abundantly available in wet years • It resorts to larger, harder seeds in dry years • The Grants found out that the beak depth changed predictably year after year
Fig. 2.11 Large-beaked finches increase in number 2.4 The Beaks of Darwin’s Finches Small-beaked finches are more common The Grants’ research supported Darwin’s hypothesis
Darwin believed that the Galapagos finches all evolved from a single common ancestor The ancestor came from the South American mainland New arrivals occupied different niches and were subject to different environmental pressures This resulted in a cluster of species A phenomenon termed adaptive radiation 2.5 How Natural SelectionProduces Diversity
The 14 finch species that Darwin studied now occupy four types of niches 1. Ground finches 2. Tree finches 3. Warbler finches 4. Vegetarian finch 2.5 How Natural SelectionProduces Diversity
Gr. logos, study of Gr. oikos, house 2.6 What is Ecology? • The term was coined by Ernst Haeckel (1866) Ecology Thus, ecology is the study of how organisms interact with their environment
2.6 What is Ecology? • There are five levels of ecological organization • 1. Populations • Individuals of the same species living together • 2. Communities • Populations of different species living together • 3. Ecosystems • Combination of communities and associated non-living factors
2.6 What is Ecology? • There are five levels of ecological organization • 4. Biomes • Major terrestrial assemblages of organisms that occur over wide geographical areas • 5. The Biosphere • All biomes together with marine and freshwater assemblages
Sun Plants Herbivores Carnivores Food chain 2.7 A Closer Look at Ecosystems • Ecosystems: the fundamental units of ecology • All organisms in an ecosystem require energy • Almost all energy comes from the sun • Energy is lost at each step of the food chain • This limits the number of steps
2.7 A Closer Look at Ecosystems Raw materials are not used up when organisms die • They are recycled back into the ecosystem for use by other organisms Rainfall and temperature are the two most important factors limiting species distribution • These physical conditions with their sets of similar plants and animals are called biomes
The niche of a species may be defined as its biological role in the community It is not synonymous with habitat Habitat place Niche pattern of living 2.8 How Species Evolve to Occupy Different Niches Within an Ecosystem
The principle of competitive exclusion No two species with the same niche can coexist Persistent competition is rare in nature So species try to find ways to reduce competition In resource partitioning, species avoid competition by 1. Living in different portions of the habitat 2. Using different resources 2.8 How Species Evolve to Occupy Different Niches Within an Ecosystem
Fig. 2.15 Resource partitioning among sympatric lizard species Anolis lizards Same pattern has evolved independently on different Caribbean Islands
Character displacements The changes that evolve in two species to reduce niche overlap This is clearly seen among Darwin’s finches 2.8 How Species Evolve to Occupy Different Niches Within an Ecosystem
Fig. 2.16 Character displacement in Darwin’s finches (genus Geospiza) Bills of similar sizes when living apart Bills of different sizes when living together
– (death + emigration) 2.9 Patterns of Population Growth • Innate capacity for increase • The rate at which a population grows in the absence of limits • Also termed the biotic potential • Realized rate of population increase (r) • # of individuals added minus the # lost • Thus: r = (birth + immigration)
Exponential Growth • To determine the population growth rate, r must be adjusted for population size # of individuals in the population population growth rate = rN Realized rate of population growth • A population exhibits exponential growth at first • However, the growth rate slows down as resources become depleted
K – N K Carrying Capacity (K) • Is the number of individuals that can be supported in a particular area indefinitely • Population growth is limited by shortages of some important factor • Space, water, nutrients • Growth of a population is approximated by the following logistic growth equation population growth rate = rN
Fig. 2.18 • This relationship is graphically represented as a sigmoid growth curve Growth fluctuates around K Exponential growth at first
Life History Strategies • The particular set of adaptations that adjusts an organism’s growth rate to its environment Rapid growth Slow growth Short lifespan Long lifespan Transient environments Stable environments Large no. of offspring Small no. of offspring No parental care Parental care
Fig. 2.20 K-selected life history Fig. 2.19 r-selected life history Life History Strategies
2.10 Human Populations • Throughout most of our history, human populations have been regulated by • Food availability • Disease • Predators • Two thousand years ago, the human population was ~ 130 million • It took one thousand years for it to double • And another 650 years for it to double again
2.10 Human Populations • Starting in the 1700s, technological changes gave humans more control over their environment • These changes allowed humans to expand the carrying capacity of their habitats • Currently, the human population is growing at a rate of ~ 1.3% annually • Doubling time at this rate is only 54 years!
Population Pyramids • Human population growth is not uniform
Fig. 2.22 Population Pyramids • Some countries, like Mexico, are currently growing rapidly Birth rate much higher than death rate
More or less rectangular pyramid => Stable population Fig. 2.23 Population Pyramids • A population’s age structure and sex ratio can be used to assess its demographic trends Triangular pyramid => Rapid future growth
Consumption in the Developed World • The vast majority of the world’s population is in developing countries • However, the vast majority of resource consumption is in the developed world • This disparity can be quantified by calculating the ecological footprint • The amount of productive land required to support a person throughout his or her life
Fig. 2.24 Ecological footprint of individuals in different countries Resource use by humans is now 1/3 greater than the amount that nature can sustainably replace
