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5 Ecosystems and Living Organisms Overview of Chapter 5 Evolution: How Populations Change Over Time Natural Selection Principles of Population Ecology Biological Communities Symbiosis Predation & Competition Species Richness in Community Community Development © 2012 John Wiley & Sons, Inc. All rights reserved. Evolution The cumulative genetic changes that occur in a population of organisms over time Current theories proposed by Charles Darwin, a 19th century naturalist Occurs through natural selection Natural Selection Individuals with more favorable genetic traits are more likely to survive and reproduce Frequency of favorable traits increase in subsequent generations © 2012 John Wiley & Sons, Inc. All rights reserved. Natural Selection Based on four observations about the natural world: 1. 2. 3. 4. High Reproductive Capacity Heritable Variation Limits on Population Growth, or a Struggle For Existence Differential Reproductive Success © 2012 John Wiley & Sons, Inc. All rights reserved. Natural Selection Darwin’s finches exemplified the variation associated with natural selection © 2012 John Wiley & Sons, Inc. All rights reserved. The Modern Synthesis An attempt to explain variation among offspring (mutation) Includes knowledge from genetics, classification, developmental biology, fossils and ecology © 2012 John Wiley & Sons, Inc. All rights reserved. Principles of Population Ecology Population Ecology Study of populations and why their numbers change over time Important for Endangered species Invasive species Population Group of individuals of same species living in the same geographic area at the same time © 2012 John Wiley & Sons, Inc. All rights reserved. Domains of Life © 2012 John Wiley & Sons, Inc. All rights reserved. Major characteristics of a population 1) Size – number of individuals 2) Density – number of individuals in a certain space 3) Dispersion – spatial pattern of a population 4) Age distribution – proportion of individuals of each age in a population © 2012 John Wiley & Sons, Inc. All rights reserved. Population Dynamics Population dynamics - study of how population change in size, density and age. -- populations respond to their environment -- change according to distribution © 2012 John Wiley & Sons, Inc. All rights reserved. Population Spacing Dispersal patterns of a population Provides insight into the environmental associations & social interactions of individuals in population clumped random uniform © 2012 John Wiley & Sons, Inc. All rights reserved. Clumped Pattern (most common) © 2012 John Wiley & Sons, Inc. All rights reserved. Uniform May result from direct interactions between individuals in the population territoriality © 2012 John Wiley & Sons, Inc. All rights reserved. Population Density Population density The number of individuals of a species per unit area or volume at a given time Ex: minnows per Liter of pond water Ovals below have same population, and different densities © 2012 John Wiley & Sons, Inc. All rights reserved. Population Size Births and immigration add individuals to a population. Births Immigration Changes to population size adding & removing individuals from a population PopuIation size birth death immigration emigration Emigration Deaths Deaths and emigration remove individuals from a population. © 2012 John Wiley & Sons, Inc. All rights reserved. Growth Rate The rate of change of a population’s size, expressed as percent per year =b−d r = growth rate, b = births/1000 people, d = deaths/1000 people r Ex: A hypothetical human population has10,000 people, and 200 births per year (20 births per 1000 people) and 100 deaths per year (10 deaths per 1000 people) = (20 / 1000) – (10 / 1000) r = 0.02 − 0.01 = 0.01, or 1% per year r © 2012 John Wiley & Sons, Inc. All rights reserved. Change in Population Size © 2012 John Wiley & Sons, Inc. All rights reserved. Change in Population Size In local populations, such as the population of the United States, the number of births, deaths, immigrants, and emigrants affects population size. © 2012 John Wiley & Sons, Inc. All rights reserved. Calculating Population Change Growth rate Death rate Emigration rate r = (b – d) + (i – e) Birth rate Immigration rate Birth (b), Death (d), Immigration (i) and Emigration (e) are calculated per 1000 people © 2012 John Wiley & Sons, Inc. All rights reserved. LIMITS TO POPULATION GROWTH Intrinsic rate of increase (r): rate at which a population would grow if it had unlimited resources Biotic potential: capacity for population growth organisms with a high biotic potential reproduce early in life have short generation times can reproduce many times have offspring each time they reproduce © 2012 John Wiley & Sons, Inc. All rights reserved. LIMITS TO POPULATION GROWTH: Resources & Competition Environmental resistance: all factors that act to limit the growth of a population Prevent indefinite reproduction Unfavorable food, water, shelter, predation, etc. Carrying Capacity (K) Maximum # of individuals an environment can support Causes leveling off of exponential growth S- shaped curve of logistic population growth © 2012 John Wiley & Sons, Inc. All rights reserved. Maximum Population Growth Intrinsic Rate of Growth (Biotic Potential) Growth rate under ideal conditions J- Shaped Curve (exponential growth) © 2012 John Wiley & Sons, Inc. All rights reserved. Logistic Growth Rapid exp. growth followed by steady dec. in pop. Growth w/time until pop. Size levels off © 2012 John Wiley & Sons, Inc. All rights reserved. Exponential Growth EXPONENTIAL GROWTH - Population w/few resource limitations; grows at a fixed rate © 2012 John Wiley & Sons, Inc. All rights reserved. Population growth change in population = births – deaths Exponential model (ideal conditions) dN = riN growth increasing at constant rate dt N r ri t d = # of individuals = rate of growth = intrinsic rate = time = rate of change every pair has 4 offspring every pair has 3 offspring intrinsic rate = maximum rate of growth © 2012 John Wiley & Sons, Inc. All rights reserved. Population Crash Overshooting carrying capacity can lead to population crash Abrupt decline in population density © 2012 John Wiley & Sons, Inc. All rights reserved. Types of Population Change Curves in Nature Population sizes may stay the same, increase, decrease, vary in regular cycles, or change erratically. Stable: fluctuates slightly above and below carrying capacity. Irruptive: populations explode and then crash to a more stable level. Cyclic: populations fluctuate and regular cyclic or boom-and-bust cycles. Ex: Lynx & snowshoe hare Irregular: erratic changes possibly due to chaos or drastic change. Ex: Algae, insects © 2012 John Wiley & Sons, Inc. All rights reserved. Simplified Population Change Curves Number of individuals © 2004 Brooks/Cole – Thomson Learning (3) Irregular (1) Stable (4) Cyclic (2) Irruptive Time © 2012 John Wiley & Sons, Inc. All rights reserved. Regulation of population size Limiting factors density dependent competition: food, mates, nesting sites predators, parasites, pathogens density independent abiotic factors sunlight (energy) temperature rainfall swarming locusts © 2012 John Wiley & Sons, Inc. All rights reserved. Factors That Affect Population Size Density Dependent Factor Factor whose effect on population changes as population density changes Examples: Predation Disease Competition Sometimes cause Boom-or-Bust Population Cycles © 2012 John Wiley & Sons, Inc. All rights reserved. Boom-Or-Bust Population Cycles © 2012 John Wiley & Sons, Inc. All rights reserved. Factors That Affect Population Size Density Independent Factors Factors that affects population size, but is not influenced by changes in population density Examples: Killing frost Severe blizzard Fire © 2012 John Wiley & Sons, Inc. All rights reserved. Population density population area = pop density What is the density of people in USA? (all 50 states) population in 2002 = 276,768,280 area = 3,536,342 sq miles © 2012 John Wiley & Sons, Inc. All rights reserved. Birth Rates births in one year X 100 = birth rate % per year total population Then change answer to births per 1000 What is the birth rate for Siberian tigers? 18 Siberian tigers were born in captivity last year and the total world population is 450. ANS = 4% and 4 100 = 40 forty per thousand 1000 © 2012 John Wiley & Sons, Inc. All rights reserved. Doubling time (how long for the population to increase by 100%?) 70____ g as a % = doubling time How many years for California to double its population with a current growth rate of 1.07% ? ANS: = 65 years © 2012 John Wiley & Sons, Inc. All rights reserved. Death Rates deaths in one year X 100 = death rate % per year total population What is the death rate in Calif? deaths in 2001 = 232,790 total population in 2001 = 34,655,000 ANS = 0.67% and 6.7 per thousand © 2012 John Wiley & Sons, Inc. All rights reserved. Reproductive Strategies r-selected species K-selected species - Small body size - - - - - Early maturity Short life span Large broods Little or no parental care Probability of long term survival is low Mosquitoes and Dandelions - Small broods Long life span Slow development Large body size Late reproduction Low reproductive rate Redwood trees and human beings © 2012 John Wiley & Sons, Inc. All rights reserved. Survivorship LATE LOSS -High survivorship to certain age; then high mortality -EX: elephants, rhinos, humans CONSTANT LOSS -Fairly constant death rate at all ages -EX: songbirds EARLY LOSS -Survivorship is low early in life -EX: annual plants, bony fish sp © 2012 John Wiley & Sons, Inc. All rights reserved. Survivorship curves What do these graphs tell about survival & strategy of a species? Generalized strategies Survival per thousand 1000 Human (type I) Hydra (type II) I. High death rate in post-reproductive years 100 II. Constant mortality rate throughout life span Oyster (type III) 10 1 0 25 50 75 Percent of maximum life span 100 III. Very high early mortality but the few survivors then live long (stay reproductive) © 2012 John Wiley & Sons, Inc. All rights reserved. Metapopulations A set of local populations among which individuals are distributed in distinct habitat patches across a landscape Source habitats Sink habitats © 2012 John Wiley & Sons, Inc. All rights reserved. Metapopulations © 2012 John Wiley & Sons, Inc. All rights reserved. Biological Communities Communities vary greatly in size and lack precise boundaries © 2012 John Wiley & Sons, Inc. All rights reserved. Ecological Niche The totality of an organisms adaptations, its use of resources, and the lifestyle to which it is fitted Takes into account all aspect of an organisms existence. IT’S ROLE Physical, chemical, biological factors needed to survive Habitat Abiotic components of the environment © 2012 John Wiley & Sons, Inc. All rights reserved. Ecological Niche Fundamental niche Potential idealized ecological niche Realized niche The actual niche the organism occupies and uses resources. Ex: Green Anole and Brown Anole © 2012 John Wiley & Sons, Inc. All rights reserved. Ecological Niche Green Anole and Brown Anole Fundamental niches of 2 lizards initially overlapped Brown anole eventually out-competed the green anole, thereby reducing the green anole’s realized niche © 2012 John Wiley & Sons, Inc. All rights reserved. Limiting Resources Any environmental resource that, because it is scarce or at unfavorable levels, restricts the ecological niche of an organism © 2012 John Wiley & Sons, Inc. All rights reserved. Competition Interaction among organisms that vie for the same resource in an ecosystem Intraspecific Competition between individuals in a population Interspecific Competition between individuals in 2 different species © 2012 John Wiley & Sons, Inc. All rights reserved. Interspecific Competition © 2012 John Wiley & Sons, Inc. All rights reserved. competition for nesting sites © 2012 John Wiley & Sons, Inc. All rights reserved. marking territory = competition © 2012 John Wiley & Sons, Inc. All rights reserved. Competitive Exclusion & Resource Petitioning Competitive Exclusion One species excludes another from a portion of the same niche as a result of competition for resources Resource Partitioning (below) Coexisting species’ niche differ from each other © 2012 John Wiley & Sons, Inc. All rights reserved. Symbiosis An intimate relationship between members of 2 or more species Participants may be benefited, harmed or unaffected by the relationship Result of coevolution Three types of symbiosis Mutualism Commensalism Parasitism © 2012 John Wiley & Sons, Inc. All rights reserved. Mutualism Symbiotic relationship in which both members benefit Ex: Mycorrihzal fungi and plant roots Fungus provides roots with unavailable nitrogen from soil Roots provide fungi with energy produced by photosynthesis in the plant Left: root growth without fungi Right: root growth with fungi © 2012 John Wiley & Sons, Inc. All rights reserved. Commensalism Symbiotic relationship where one species benefits and the other is neither harmed nor helped Ex: epiphytes and tropical trees Epiphytes uses tree as anchor Epiphyte benefits from getting closer to sunlight, tropical tree is not affected © 2012 John Wiley & Sons, Inc. All rights reserved. Parasitism Symbiotic relationship in which one species is benefited and the other is harmed Parasites Ex: rarely kill their hosts ticks Ticks attach themselves to skin of animals and consume their blood © 2012 John Wiley & Sons, Inc. All rights reserved. Predation The consumption of one species by another Many predator-prey interactions Most common is pursuit and ambush Plants and animals have established specific defenses against predation through evolution © 2012 John Wiley & Sons, Inc. All rights reserved. Pursuit and Ambush Pursuing prey - chasing prey down and catching it Ex: Day gecko and spider (below) Ambush - predators catch prey unaware Camouflage Attract prey with colors or light © 2012 John Wiley & Sons, Inc. All rights reserved. Plant Defenses Against Herbivores Plants cannot flee predators Adaptations Spikes, thorns, leathery leaves, thick wax Protective chemicals that are poisonous or unpalatable © 2012 John Wiley & Sons, Inc. All rights reserved. Defensive Adaptation of Animals Fleeing or running Mechanical defenses Ex: quills of porcupines, shell of turtles Living in groups Camouflage Chemical defensespoisons Ex: brightly colored poison arrow frog © 2012 John Wiley & Sons, Inc. All rights reserved. Keystone Species A species that exerts profound influence on a community More important to the community than what would be expected based on abundance The dependence of other species on the keystone species is apparent when the keystone species is removed Protecting keystone species is a goal to conservation biologists © 2012 John Wiley & Sons, Inc. All rights reserved. Species Richness The number of species in a community Tropical rainforests = high species richness Isolated island = low species richness Related to the abundance of potential ecological niches © 2012 John Wiley & Sons, Inc. All rights reserved. Ecosystem Services Important environmental benefits that ecosystems provide, such as: Clean air to breathe Clean water to drink Fertile soil in which to grow crops © 2012 John Wiley & Sons, Inc. All rights reserved. © 2012 John Wiley & Sons, Inc. All rights reserved. Community Development Succession: the process where a community develops slowly through a series of species Earlier species alter the environment in some way to make it more habitable by other species As more species arrive, the earlier species are outcompeted and replaced Two types of succession Primary succession Secondary succession © 2012 John Wiley & Sons, Inc. All rights reserved. Primary Succession Succession that begins in a previously uninhabited environment No soil is present Ex: bare rocks, cooled lava fields, etc. General Succession Pattern Lichen secrete acids that crumble the rock (soil begins to form) Lichen mosses grasses shrubs forests © 2012 John Wiley & Sons, Inc. All rights reserved. 1 2 3 Primary Succession 1. 2. 3. Barren landscape rock with lichen & small shrubs Dwarf trees & shrubs Spruces dominate © 2012 John Wiley & Sons, Inc. All rights reserved. Secondary Succession Succession that begins in an environment following destruction of all or part of the earlier community Ex: abandoned farmland, open area after fire Generally occurs more rapidly than primary succession © 2012 John Wiley & Sons, Inc. All rights reserved. Secondary Succession of an abandoned farm field in North Carolina © 2012 John Wiley & Sons, Inc. All rights reserved.
