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What is Evolution and how has it led to the current diversity of organisms on the Earth?

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Presentation on theme: "What is Evolution and how has it led to the current diversity of organisms on the Earth?"— Presentation transcript:

1 What is Evolution and how has it led to the current diversity of organisms on the Earth?

2 How It All Began! It is impossible for life to have evolved with oxygen No oxygen in atmosphere (CO 2, CH 4, CO, N 2 & H 2 O) Cyanobacteria photosynthesis Anaerobic prokaryotes-> photosynthetic prokaryotes- >aerobic prokaryotes-> eukaryotes-> multicellualr organisms

3 What is Evolution and Natural Selection? Evolution : Cumulative genetic changes over time in a population Natural Selection : Hypothesis proposed by Charles Darwin in 1859; The process in which better adapted individuals are more likely to survive and reproduce, increasing their proportion in the population (Survival of the Fittest)

4 How Does Natural Selection Work? Overproduction: Each species produces more offspring than will survive. Variation: Each individual exhibits a unique combination of traits. Limited Resources: There is only so much food, water, light, growing space. Differential Reproductive Success: Those individuals with the most favorable combination of traits are more likely to survive, reproduce and pass their traits to the next generation.

5 Types of Natural Selection Directional Selection: Favors one extreme phenotype (antibiotics killing bacteria) Stabilizing Selection: Favors average phenotype (birth weight) Disruptive Selection: Favors both extremes (bill size in the finches) Which of these selections favors diversity?

6 Life is a Genetic Dice Game A populations ability to adapt is limited by its gene pool (genetic composition) and how fast it can reproduce. Microevolution: small genetic changes that a population within a species undergoes (peppered moth in England) Macroevolution: Long term, large scale changes through which new species form from ancestral species and other species are lost through extinction. Coevolution: Two different species interact over a long time, changes in gene pool of one species can lead to changes in the gene pool of the other.

7 How does the gene pool change? Individuals do not evolve! Populations do. Sexual Selection: Females select males with better resources Mutation: Occurs constantly (random) Migration: Tends to eliminate genetic differences in populations by equalizing allele frequencies: But causes increased diversity in small populations (animal swapping in zoos) Genetic Drift: Change in allele frequency due to random chance (more pronounced in small populations) Bottlenecking: event in which a significant percentage of a population or species is killed or otherwise prevented from reproducing, and the population is reduced by 50% or more, often by several orders of magnitude (cheetahs: lots of inbreeding & loss of allele frequencies)

8 What Limits Adaptation? Reproductive Strategies: K-selected species: large body size, long life spans, slow development, late reproduction, low reproductive rate, parental care (elephants, whales) R-selected species: small body size, early maturity, short life span, large broods, little or no parental care (insects, weeds, mice) Many species posses a combination as well as traits that are neither Which strategy has a better chance of surviving a large disturbance? Why?

9 What is the probability of survivorship? Type I survivorship curves : are for species that have a high survival rate of the young, live out most of their expected life span and die in old age. (Humans) Type II survivorship curves : are for species that have a relatively constant death rate throughout their life span. Death could be due to hunting or diseases. (coral, squirrels, honey bees and many reptiles) Type III survivorship curves : are found in species that have many young, most of which die very early in their life. (Plants, oysters and sea urchins)

10 Which type of survivorship curve does the cheetah have? What does parental care have to do with the shape of these curves?

11 SURVIVAL HANGS IN THE BALANCE! When facing a new powerful selective pressure, such as climate change or a new species invading the ecosystem, species have three alternatives: Adaptation Migration Extinction



14 SIMSPSON INDEX n = the total number of organisms of a particular species N = the total number of organisms of all species The value of D ranges between 0 and 1 With this index, 0 represents infinite diversity and 1, no diversity. Simpson's Index of Diversity 1 – D Simpson's Reciprocal Index 1 / D

15 How do new species evolve? Reproductive Isolation: Original population must separate into smaller populations that do not interbreed Geographical: Mountains/rivers/cities Spatial: Distance (maple trees in NJ & Maine) Temporal: Timing of reproductive events Morphological: chihuahua & great dane Physiological: Chemical signals in plants to allow pollen in

16 Separated Populations must be Exposed to Different Selective Pressures! Geographic Isolation: Due to glaciation in North America fox population was separated In the Arctic, selective pressure favored heavier fur, shorter tail, legs, ears and nose and white fur all of which would be harmful in warmer climates Therefore speciation occurred: arctic fox/gray fox

17 How are Species Interconnected? Symbiosis: Individuals of one species live in or on another species. Mutualism: Both species benefit (Nitrogen fixing bacteria live in nodules in the roots of legumes) Commensalism: One species benefits without harming the other (barnacles on whales) Parasitism: One organism obtains nourishment (parasite) from another (host). Parasites may weaken its host but rarely kills (tapeworms).

18 Predator – Prey Relationships Predator chases and the prey avoids Countless Strategies Camouflage & Mimicry Being Big (elephant) Groups (odds of being caught is less) Fast, hide Plants: spines, thorns, tough leaves, toxic

19 Whats all this Competition About? Competition: Interaction among organisms that vie for the same resources such as food or living space Interspecific Competition: Competition between different species (hyenas and lions) How can interspecific competition be avoided? Eating at different times Resource partitioning Character displacement

20 More Competition! Intraspecific Competition: Competition among individuals within a population (two male lions) The competitive exclusion principle: (Gause's Law) states that two species that compete for the exact same resources cannot stably coexist.Gause'sspecies Competition can lead to character displacement. If this occurs long enough you get speciation (different beak sizes eat different types of food)

21 Why is Biodiversity So Important? 1.8 million species identified so far 99% of all species that ever lived are now extinct 25% of all mammals are at risk of becoming extinct in the wild in near future Highest risk are apes & mammals

22 What roles do various species play? Niche: The role of a species in the community or way of life Keystone species: Have a larger effect on the types and abundance of other species in the community (otters, bats, sea stars)

23 Going, Going, Gone! Indicator species: Species that serve as early warnings of damage or danger to a community. Why are amphibians (frogs) indicator species? Life in both water/land Thin absorbent skin

24 Feedback Loops Positive Feedback: change increases condition already present Negative Feedback: change decreases condition already present

25 All Species Are Important! Ecological Value: Each species plays a role to increase resilience (ability of ecosystem to bounce back after a disturbance) Economic Value: 7 yr old lion in Kenya is worth $515, 000 in tourist attraction Medical & Scientific Value: 25% of all medicine derived from plants (Taxol) Intrinsic Value: Regardless of usefulness all species morally have value (aesthetic)

26 How do ecosystems respond to change? Primary Succession: Establishing life on lifeless ground (bare rock) Secondary Succession: Life building on life. Life emerges again after a disturbance. Aquatic Succession: Water to land

27 How Do Species Replace One Another? Facilitation: One set of species makes an area suitable for another (mosses and lichens build up soil on rocky areas for grasses and herbs to grow) Inhibition: Early species hinder the growth of other species (release toxic chemicals, walnut trees) Tolerance: Late successional plants are unaffected by plants at earlier stages.

28 Biodiversity on an Island Theory of Island Biogeography (MacArthur & Wilson) states that two factors affect biodiversity on an island, immigration & extinction. Two features of islands affect immigration and extinction, size & distance from nearest mainland What size island would have more biodiversity? Why? Which distance would have more biodiversity? Why?

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