1!What is Ecology? Ernst Haeckel (1866) – from Greek term for home “Oikos”. “The total relations between an organism and its organic and inorganic environment.” What is Ecology? Molles – “The study of the relationships between organisms and the environment.” What is Ecology? Townsend, Harper, and Begon (2000) – “The scientific study of the distribution and abundance of organisms and the interactions that determine distribution and abundance.” What is Ecology? Houlihan (Today) – “The scientific study of the patterns of distribution and abundance of organisms and the mechanisms that determine the patterns of distribution and abundance.” Ecology • Patterns - distribution and abundance • Mechanisms - interactions between organisms and their environments – both non-living (abiotic) and living (biotic) components of the environment. • Focus - distinguished by the level of organization at which ecologists work. Levels of Organization2!Levels of Organization • Organism - an individual animal • Population - groups of individuals of same species inhabiting an area. • Community – groups of populations in an area. • Ecosystem – communities and non-living components. • Biosphere – the entire earth system. Why study population ecology? The environment of an organism consists of anything that might effect its chance to survive and reproduce. When we model the ecology of an organism we only include those components of the environment that matter. What are the components of an organism’s environment? Abiotic - non-living (nutrients, climate, etc.) Biotic - living Population Dynamics: The patterns of and mechanisms of population change.3!Population growth and regulation simple model of population growth: change in pop size = births - deaths ∆N = B - D (ignoring immigration and emigration) example: • population of 10,000 people • in one year, 1500 births and 500 deaths • ∆N = 1000 But more useful to think in terms of rate. In our example, per capita birth rate: 1500 births ÷ 10,000 people = 0.15 births/person/year per capita death rate: 500 deaths ÷ 10,000 people = 0.05 deaths/person/year Defining per capita growth rate r = b - d (b = per capita birth rate, d = per capita death rate) In our example, r = 0.15 - 0.05 = 0.1 or 0.1 person per capita per year or 10% per year per capita growth rate, continued r = b -d Note that: r > 0, population is growing r < 0, population is shrinking r = 0, population is stable It follows that: ΔNΔt= rNExponential Growth Equation! in our example, r = 0.1, so year 1 year 2 year3 ΔNΔt= rN ΔNyear= 0.1(10,000) = 1000_people ΔNyear= 0.1(11,000) =1100_people ΔNyear= 0.1(12,100) = 1210_people4!exponential growth • If r remains constant (and > 0), the number of individuals added to the population each year grows continuously. In our model, the amount of time required for an exponentially growing population to increase from 2 to 2000 individuals is determined by 1. how quickly the value of r increases. 2. the amount of genetic drift that occurs during population growth. 3. the size of the difference between per capita birth rate (b) and per capita death rate (d). 4. the size of the per capita growth rate (r) 5. two of the above exponential growth • If r remains constant (and > 0), the number of individuals added to the population each year grows continuously. • curve has no upper limit • population size increases more rapidly when r is larger. exponential growth, continued • a population has a hypothetical maximum possible value of r • the intrinsic rate of increase, rmax • represents a population’s growth rate under ideal conditions (unlimited resources)5!In the real world, populations do not maintain exponential growth. House Flies If each fly lays 100 eggs and generation time is approx. 2 weeks then No. of flies in 1 year =1052 10,000,000,000,000,000,000,000,000,000 Problem of unlimited growth In the real world, populations do not maintain exponential growth. • population growth approaches a limit • r declines • eventually, a limit is reached • r = 0 • population has reached its maximum sustainable size (carrying capacity) • designated K Exponential growth Population size increases indefinitely at a rate determined by the rate of increase. Exponential growth dNdtrN=Change in population size over change in time Exponential growth6!Logistic growth Population size increases at a increasing rate and then at a diminishing rate, until it reaches a limit called the carrying capacity (K). Logistic growth N t K Logistic growth dNdt= rmaxNK -NKGrowth limiting component!In logistic growth, per capita growth rate is closest to rmax when 1. population size is high 2. population size is low. 3. (K - N) approaches 0 4. (K - N) approaches K 5. two of the above answers are correct.7!Real-world and lab populations may follow logistic growth pattern • especially in periods after populations have been reduced. What limits population growth? (By affecting birth rate and/or death rate) What limits population growth? (By affecting birth rate and/or death rate) • density-dependent factors (effects increase as population density increases)8!Which of the following processes is NOT likely to supply density-dependent negative feedback on population growth? 1. predation 2. competition 3. parasitism 4. seasonal climate change 5. accumulation of waste products What limits population growth? (By affecting birth rate and/or death rate) • density-dependent factors (effects increase as population density increases) – predation • including parasitism – availability of resources • e.g. food, space – accumulation of wastes – behavior change What limits population growth? (By affecting birth rate and/or death rate) • density-dependent factors (effects increase as population density increases) • density-independent factors – weather • e.g. annual freezes, periodic droughts/floods, unpredictable storms, etc. Other factors affecting growth rates • sex ratio • age