Ch.5 Evolution and Community Ecology How do organisms become so well suited to their environment? Evolution and Natural Selection

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1 Ch.5 Evolution and Community Ecology How do organisms become so well suited to their environment? Evolution and Natural Selection Gene: A sequence of DNA that codes for a particular trait Gene pool: All the genes present in a population Biological evolution: The change in a population s gene pool over time Mutation Accidental change in DNA that can give rise to variation among individuals Migration (gene flow) Movement of individuals into (immigration) or out of (emigration) a population 1

2 Genetic Drift: Evolution that occurs by chance. Charles Darwin, in 1859, proposed the theory of natural selection. Natural Selection: Process by which traits useful for survival and reproduction are passed on more frequently than those that are not (Some individuals, because of certain inherited traits, are more likely to survive and reproduce than other individuals, based on the environment they are living in.). Over time, natural selection can cause characteristics of the population to change this is known as evolution. Adaptation = an inherited trait that increases an organism's chance of survival and reproduction Coevolution = two species evolving in response to long term interactions with each other (ex: termites and bacteria in their gut) 2

3 Conditions of Natural Selection: (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. Fitness describes how reproductively successful an organism is for its environment. 3

4 Artificial Selection Selection under human direction Throughout history, humans have chosen and bred animals and plants with beneficial traits. 4

5 Speciation Process by which new species are generated Can occur in a number of different ways; the most important way is called allopatric speciation Has resulted in every form of life on Earth today and in the past 5

6 Extinction The disappearance of species from Earth Generally occurs gradually, one species at a time, when environmental conditions change more rapidly than the species can adapt There are five known mass extinction events, each of which wiped out a large proportion of Earth s species. Trilobites Marine arthropods that went extinct at the end of the Permian period. 6

7 5.2 Species Interactions The Niche Describes an organism s use of resources and functional role in a community Affected by an organism s tolerance its ability to survive and reproduce under changing environmental conditions Often restricted by competition A big part of a spider's niche, or role is to prey on insects caught in its web. 7

8 Competition Organisms compete when they seek the same limited resource. 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. By each specializing in particular insects on particular parts of the trees, the birds minimize competition. 8

9 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. 9

10 Parasitism and Herbivory Parasitism: One organism (the parasite) relies on another (the host) for nourishment or for some other benefit symbosis a ;long lasting and physically close relationship in which at least one organism benefits. Herbivory: An animal feeding on a plant 10

11 Mutualism and Commensalism Mutualism: a relationship in which two or more species benefit Commensalism: a relationship in which one species benefits while the other is unaffected Lichen: a symbiotic relationship between a fungus and a photosynthetic partner, such as an alga 11

12 5.3 Ecological Communities Primary Producers (Autotrophs) Capture energy from the sun or from chemicals and store it in the bonds of sugars, making it available to the rest of the community Energy from the sun is captured by plants, algae, or bacteria through photosynthesis. Energy from chemicals is captured by some bacteria through chemosynthesis. 12

13 Consumers (Heterotrophs) Rely on other organisms for energy and nutrients Herbivores: plant eaters Carnivores: meat eaters Omnivores: combination eaters Detritivores and decomposers: recycle nutrients within the ecosystem by breaking down nonliving organic matter Use oxygen to break bonds in sugar and release its energy through cellular respiration (primary producers do this, too) The California Condor Scavengers, such as vultures and condors, are just large detritivores. 13

14 Energy in Communities An organism s rank in a feeding hierarchy is its trophic level. Primary producers always occupy the first trophic level of any community. In general, only about 10% of the energy available at any trophic level is passed to the next; most of the rest is lost to the environment as heat. 14

15 Numbers and Biomass in Communities A trophic level s biomass is the mass of living tissue it contains. In general, there are more organisms and greater biomass at lower trophic levels than at higher ones. 15

16 Food Chains and Webs Food chain: Linear series of feeding relationships Food web: Shows the overlapping and interconnected food chains present in a community 16

17 Keystone Species Species that have strong and/or wide reaching effects on a community Removal of a keystone species can significantly alter the structure of a community. 17

18 5.4 Community Stability Ecological Disturbances A community in equilibrium is generally stable and balanced, with most populations at or around carrying capacity. Disturbances or changes in the environment can throw a community into disequilibrium. Severe disturbances can cause permanent changes to a community and initiate a predictable series of changes called succession. 18

19 Primary Succession Occurs when there are no traces of the original community remaining, including vegetation and soil Pioneer species, such as lichens, are the first to colonize. The environment changes as new species move in, adding nutrients and generating habitat. Secondary Succession Occurs when a disturbance dramatically alters a community bu does not completely destroy it Common after disturbances such as fire, logging, or farming Occurs significantly faster than primary succession Succession in Water Primary aquatic succession occurs when an area fills with water for the first time. Disturbances such as floods or excess nutrient runoff can lead to secondary aquatic succession. 19

20 Climax Communities Ecologists once thought succession leads to stable climax communities. Today, ecologists see communities as temporary, ever changin associations of species. Communities are influenced by many factors and constant disturbances. 20

21 Invasive Species Nonnative organisms that spread widely in a community A lack of limiting factors such as predators, parasites, or competitors enables their population to grow unchecked. Not all invasive species are harmful. 21

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