Evolution and Community Ecology

Transcription

1 CHAPTER 5 Evolution and Community Ecology Black and White, and Spread All Over Zebra mussels and quagga mussels were accidentally introduced into Lake St. Clair in the late 1980s. They have since spread throughout the Great Lakes system and connecting rivers. The invasive mussels have a high economic and ecological cost. Talk About It The Great Lakes are home to more than 20 native mussel species. Why are the zebra and quagga mussels so much more destructive than the lakes native mussels? Scientists have identified and described over 1.5 million species. Millions more have yet to be discovered. a. Evolution and Natural Selection A starting population of dogs. Genes control the color and pattern of the dogs coats. Evolution: change over time i. Over time, changes occur in the gene pool... All the genes present in a population ii. Gene: A sequence of DNA that codes for a particular trait b. Mechanisms of Evolution: i. Mutations changes in DNA that can give rise to variation among individuals; can be good changes (such as stripes or no stripes in fish) or harmful Mechanisms of Evolution: ii. Migration (gene flow) A change in the proportion of organisms with a certain trait due to moving away of one group 1

2 Mechanisms of Evolution iii. Genetic Drift Evolution that occurs by chance : Natural disasters can result in change in population density and type II. Natural Selection a. Conditions of Natural Selection iv. Natural Selection Propagation of traits that enhance an organisms survival; the strongest organisms will survive, passing on best traits. (1) Organisms produce more offspring than can survive. (2) Individuals vary in characteristics, some of which are heritable. (3) Individuals vary in fitness, or reproductive success; this is reflected in their habitat II. Natural Selection a. Conditions of Natural Selection 1. Fitness how reproductively successful and organism is. b. Artificial Selection i. Process of selection (of traits) based on human intervention. 2. Adaptations trait that increases an organisms ability to survive iv. Survival of the fittest the most fit animal will produce more offspring and pass on genes more frequently than ones of lower fitness ii. Animals many varieties of dogs, which can all interbreed. Varieties are maintained by selective breeding. iii. Plants artificial selection gives us most of the food we eat today; one plant gives rise to many more. iv. Allows us to select the traits we like the most Process by which new species are generated/created Can occur in a number of different ways; the most important way is called allopatric speciation: separation for long periods of time c. Speciation Allopatric Speciation d. Extinction disappearance Trilobites Marine arthropods that went extinct at the end of the Permian period. Did You Know? During the Permo-Triassic extinction 250 million years ago, 70% of all land species and 90% of all marine species went extinct. i. 99% of all species that have ever lived are extinct ii. Fossil record shows species lasting 1-10 mill. yr Generally occurs when conditions change more rapidly than the species can adapt (background ext) There are five worldwide mass extinction events, each of which wiped out a large proportion of Earth s species. (Genesis Flood) 2

3 The zebra mussel has completely displaced 20 native mussel species in Lake St. Clair. 1. The Niche A. Habitat is the general place an organism lives. B. Niche includes where it live, eats, reproduces and interacts with others. C. Tolerance i- An organism s ability to survive and reproduce under changing environmental conditions Specialists have narrow range of tolerance (pandas) Generalists have a wide range (rats) Organisms compete when they seek the same limited resource. d. Competition In rare cases, one species can entirely exclude another from using resources. To reduce competition, species often partition resources, which can lead to character displacement. Predation (+/ ) The process by which a predator hunts, kills, and consumes prey Causes cycles in predatory and prey population sizes Defensive traits such as camouflage, mimicry, and warning coloration have evolved in response to predator-prey interactions. Some predator-prey relationships are examples of coevolution, the process by which two species evolve in response to changes in each other. Rough-Skinned Newt Did You Know? A single roughskinned newt contains enough poison to kill 100 people. Unfortunately for the newt, its predator, the common garter snake, has coevolved resistance to the toxin. Resource Partitioning Parasitism and Herbivory (+/ ) Hookworm (a parasite) Did You Know? One study of Pacific estuaries suggests that parasites play an important role in keeping these ecosystems healthy by controlling host populations. Parasitism: One organism (the parasite) relies on another (the host) for nourishment or for some other benefit Herbivory: An animal feeding on a plant Mutualism (+/+) and Commensalism (+/0) Lichen: a symbiotic relationship between a fungus and a photosynthetic partner, such as an alga Did You Know? Symbiosis describes a longlasting and physically close relationship between species in which at least one species benefits. Mutualism: a relationship in which two or more species benefit Commensalism: a relationship in which one species benefits while the other is unaffected 3

4 The sun provides the energy for almost all of the ecological communities and species interactions on Earth. A. Primary Producers (Autotrophs) i. Energy cannot be created or destroyed (1 st Law of Thermodynamics) ii. Plants capture energy from sun or chemicals and store it as sugar 1. Energy (light) from sun is the main source for photosynthesis: 6CO 2 + 6H 2 O + energy = C 6 H 12 O 6 + 6O 2 Did You Know? Deep-sea vents, far from sunlight, support entire communities of fish, clams, and other sea animals, which depend on energy converted through chemosynthesis. Primary Producers (Autotrophs) 2. Chemosynthesis - Energy from chemicals when no light is available, converts hydrogen sulfide instead of light: 6CO 2 + 6H 2 O + 3H 2 S = C 6 H 12 O 6 + 3H 2 SO 4 3. Both methods use carbon dioxide and water to make sugar Did You Know? Deep-sea vents, far from sunlight, support entire communities of fish, clams, and other sea animals, which depend on energy converted through chemosynthesis. B. Consumers (Heterotrophs) i. Organisms that rely on other organisms for energy (like us) ii. Use the sugar from photosynthesis (food) for energy iii. Use oxygen to release energy from sugar: cellular respiration : iv. 6CO 2 + C 6 H 12 O 6 = 6CO 6 + 6H 2 O California Condor Did You Know? Scavengers, such as vultures and condors, are just large detritivores. B. Types of Consumers i. Herbivores primary consumers that eat producers(plants) ii. Carnivores eat other animals iii. Omnivores eat both plants and animals iv. Detrivores eat only nonliving (dead) organisms V. Decomposers breakdown dead plants/animals so plants can use them as nutrients and the cycle starts over again. California Condor Did You Know? Scavengers, such as vultures and condors, are just large detritivores. II. Energy and Biomass a. Trophic Levels pyramid model show ranking in feeding hierarchy b. Energy i. Entropy Energy tends to move from order to disorder (2 nd Law of Thermodynamics); ii. Example of tank of gas: only about 14% gets used, rest is lost as heat iii. Organisms use energy from food but burn it in the process iv. Only 10% of energy is available for each succeeding trophic level Pyramid of Energy 4

5 Biomass in Communities c. Total amount of living tissue (plant or animal) at each trophic level i. Each level has less mass because of less available energy Food Chains and Webs a. Food Chain a linear series of feeding relationships that shows energy transfer b. Food Web more realistic model of how organisms feed on each other, because animals usually eat more than one type of food Keystone Species where one organism has big effect on whole ecosystem; without that one species, the whole system falls apart (example of sea otters) A 2010 report on invasive species suggests that they cost the U.S. $120 billion a year in environmental losses and damages. Invasive kudzu 1. Ecological Disturbances A. A community in equilibrium is generally stable and balanced, with most populations at or around carrying capacity. B. Disturbances or changes in the environment can throw a community into disequilibrium. C. Severe disturbances can cause permanent changes to a community and initiate a predictable series of changes called succession. Forest fire 2. Primary Succession a. Occurs when there are no traces of the original community remaining, including vegetation and soil. b. Pioneer species, such as lichens, are the first to colonize. c. The environment changes as new species move in, adding nutrients and generating habitat. 5

6 3. Secondary Succession a. Occurs when a disturbance dramatically alters a community but does not completely destroy it b. Common after disturbances such as fire, logging, or farming c. Occurs significantly faster than primary succession 4. Succession in Water a. Primary aquatic succession occurs when an area fills with water for the first time. b. Disturbances such as floods or excess nutrient runoff can lead to secondary aquatic succession. i. Algae add nutrients ii. Debris builds on bottom iii. Lake fills in, becomes a meadow 5. Climax Communities a. Ecologists once thought succession leads to stable climax communities. b. Today, ecologists see communities as temporary, ever-changing associations of species. c. Communities are influenced by many factors and constant disturbances. Beech-maple forest, a classic climax community 6. Invasive Species a. Nonnative organisms that spread widely in a community b. A lack of limiting factors such as predators, parasites, or competitors enables their population to grow unchecked. i. Zebra mussel ii. Cane toad iii. kudzu c. Not all invasive species are harmful. Did You Know? Although the European honeybee is invasive to North America, it is beneficial because it pollinates our agricultural crops. 6