#### Transcript Week 5 Lecture - Environmental Studies Program

Announcements • • • Check your syllabus with the one online to make sure it is the right one! No reading assignment for section this week Focus on your textbook Two-minute Quiz Imagine that you are a wetland ecologist. It is early summer, and you and your limnologist best friend are mapping a system of streams, rivers, and wetlands near the coast in northern Siberia. You ford a small, rocky, fast moving stream. True or false: Most of the litter in this stream is likely to be highly processed. • You follow the water downstream until it slows and pools in an area filled with sedges and accumulated organic matter. Are there many trees in this biome? • You hike overland to a large river that empties into the sea. You taste the water and it is brackish. The birding is great. Where are you now? (multiple answers possible for this one) • Summary from Wednesday • • • • aquatic ecosystems differences between low & high order streams production vs. biomass pyramids lakes • • • • • light penetration thermal stratification and O2 content phytoplankton and abiotic factors over the year oligotrophic vs. eutrophic wetlands • biogeochemistry Wetland Biogeochemistry • • • When land is flooded, O2 gets used up by decomposers and the soil becomes anaerobic Demand for O2 is still high Other minerals containing oxygen get reduced • • Reduction is when a compound gains an electron- in this case by giving up an O2 atom Some molecules release O2 more easily than others O2 NO3- Fe(OH)3 MnO2 SO42- CO2 • If the water level drops, O2 enters the soil again, and the reduced substances can get oxidized Saltwater vs. Freshwater Systems • Salt marshes • sulfur cycling important CO2 organic matter H2S SO42- SO42- Saltwater vs. Freshwater Systems • Freshwater systems • • decomposition is slow organic matter accumulates • • storage of carbon reduction of CO2 produces methane (CH4) O2 NO3- Fe(OH)3 MnO2 SO42- CO2 Environmental Concerns in Wetlands • Drainage • • either for agriculture and development, or to use the available water Pollution • wetlands are in low-lying areas The open ocean is most like… A) a temperate rain forest B) the chaparral C) the desert D) a Mediterranean grassland …with regard to productivity. Where is the ocean most productive? Where nutrients are available: • near the coast • rivers bring nutrients • in upwelling zones Coastal Upwelling Coastal Upwelling Off-shore winds blow southward. Coastal Upwelling Friction and the effects of the Earth's rotation cause the surface layer of the ocean to move away from the coast. Coastal Upwelling As the surface water moves offshore, cold, nutrient-rich water comes up from below, replacing it. Why are nutrients down deep? Why are surface waters low in nutrients? Euphotic zone Aphotic zone Sediment Dead material sinks to the bottom, where it is dark and photosynthesis is not taking place Coral reefs • Coral reefs are extremely • • productive Visibility is great! But we know that nutrient-rich water is murky How is this possible? Where are the nutrients? Coral reefs • Efficient cycling of nutrients • Complex relationships between organisms • zooxanthellae in coral • intricate food webs Ecology subfields: • Population Ecology: • the study of individuals of a certain species occupying a defined area during a specific time Population Ecology • Population density • # of individuals of a certain species in a given area • Population demography • a way of assessing well-being • • • • • proportion of males to females birth rates death rates replacement of parents by next generation (fitness) life expectancy The Tools of Population Ecology • • Modeling Creation of Life Tables Why are models powerful? You can use them to: • • • • • synthesize information look at a system quantitatively test your understanding predict system dynamics make management decisions Population Growth • • • • • • • t = time N = population size (number of individuals) dN = change in population size dt = change in time dN/dt = rate in change of population size r = growth constant; maximum rate of population increase K = carrying capacity; maximum population size Population Growth • Assume a fixed rate of reproduction per individual • for starters, let’s assume no limits on growth • change in number of individuals over time would be equal to the number of individuals multiplied by a growth constant dN =r*N dt • exponential growth Time (t) Population size (N) Population size (N) Can the population really grow forever? Time (t) Population size (N) Can the population really grow forever? What should this curve look like to be more realistic? Time (t) Population Growth • logistic growth • assume that as a population increases, it becomes limited by resources • growth rate should decline when the population size gets large • symmetrical S-shaped curve with an upper asymptote Announcements • Women in Science and Engineering • “Applying to Graduate School in Sciences” workshop and lunch Oct. 27th • • • • Check your syllabus with the one online to make sure it is the right one! No additional reading assignment for section this week Focus on your textbook reading Bring your calculator to section Summary from Monday • Wetland biogeochemistry • H2S production in brackish wetlands • Methane (CH4) production in freshwater wetlands Open oceans vs. coastal areas • Population ecology • • The power of modeling • Modeling exponential growth dN =r*N dt • Logitstic growth • Resources limit population growth N t Population Growth How do you model logistic growth? How do you write an equation to fit that S-shaped curve? Start with exponential growth dN =r*N dt Population Growth How do you model logistic growth? How do you write an equation to fit that S-shaped curve? Start with exponential growth dN = r * N (1 – dt N ) K Population Growth logistic growth dN = r * N (1 – dt N ) K Population Growth dN = r * N (1 – dt logistic growth so, when N is much smaller than K N ≈0 K N ) K dN = r * N (1 – 0) exponential growth dt Population Growth dN = r * N (1 – dt logistic growth so, when N is much smaller than K N ) K N dN ≈0 = r * N (1 – 0) exponential growth K dt when N is equal to K N dN ≈1 = r * N (1 – 1) no growth K dt Population Growth dN = r * N (1 – dt logistic growth so, when N is much smaller than K N ) K N dN ≈0 = r * N (1 – 0) exponential growth K dt when N is equal to K N dN ≈1 = r * N (1 – 1) no growth K dt when N is much larger than K N dN >1 = r * N (1 – 2) population shrinks K dt What is carrying capacity? • • • where births = deaths number of individuals an area can support through the most unfavorable time of year population an area can support without degradation of the habitat What limits populations? • Density-dependent factors: • intra-specific competition • food • space • contagious disease • waste production • Density-independent factors: • disturbance, environmental conditions • fire • flood • colder than normal winter Species interactions • How do we model them? • Start with logistic growth dN = r * N (1 – dt dN K =r*N( dt K N ) K - dN K-N =r*N( ) dt K N ) K Use this equation for 2 different species Species interactions • Population 1 N1 dN1 K1-N1 = r1 * N1 ( ) dt K1 • Population 2 N2 dN2 K2-N2 = r2 * N2 ( ) dt K2 • But the growth of one population should have an effect the size of the other population Species interactions • New term for interactions a12 effect of population 2 on population 1 a21 effect of population 1 on population 2 • Multiply new term by population size the larger population 2 is, the larger its effect on population 1 (and vice versa) a12 * N2 a21 * N1 Species interactions If two species are competing, the growth of one population should reduce the size of the other Population 1 N1 dN1 K1 - N1 - a12 N2 dt = r1 * N1 K1 Population 2 N2 dN2 K2 - N2 - a21 N1 dt = r2 * N2 K2 Species interactions If two species are competing, the growth of one population should reduce the size of the other Because this is a negative term, K is reduced Population 1 N1 dN1 K1 - N1 - a12 N2 dt = r1 * N1 K1 Population 2 N2 dN2 K2 - N2 - a21 N1 dt = r2 * N2 K2 Species interactions If it is a predator-prey relationship, then the two populations have opposite effects on one another Because this is a negative term, K is reduced Prey (N1) dN1 K1 - N1 - a12 N2 dt = r1 * N1 K1 Predator (N2) Because this is a positive term, K is increased dN2 K2 - N2 + a21 N1 dt = r2 * N2 K2 Species interactions If it is a mutually beneficial relationship, then the two populations increase each other’s size Because this is a positive term, K is increased Population 1 N1 dN1 K1 - N1 + a12 N2 dt = r1 * N1 K1 Population 2 N2 Because this is a positive term, K is increased dN2 K2 - N2 + a21 N1 dt = r2 * N2 K2 Problems with simple logistic growth • births and deaths not separated • you might want to look at these processes separately • predation may have no effect on birth rate • no age structure • when is a fish just a fish? Announcements • • Check your syllabus with the one online to make sure it is the right one! Bring your calculator to section Summary from Wednesday • • • Modeling Logistic Growth dN = r * N (1 – dt N ) K Limits on populations • Density-dependent • Density-independent Modeling Population Interactions dN1 K1 - N1 - a12 N2 = r1 * N1 dt K1 dN2 K2 - N2 + a21 N1 dt = r2 * N2 K2 Summary from Wednesday • • • Modeling Logistic Growth dN = r * N (1 – dt N ) K Limits on populations • Density-dependent • Density-independent Modeling Population Interactions dN1 K1 - N1 - a12 N2 = r1 * N1 dt K1 Prey dN2 K2 - N2 + a21 N1 dt = r2 * N2 K2 Predator Births and Deaths Births: As a population increases: • # of births will go up • with more individuals, more young will be born # births = birth rate * N • birth rate can go down • resources become limiting • each mother gives birth to fewer young Deaths: Background level of mortality • mortality due to old age fundamental death rate = f(N) (df) Density-dependent mortality • mortality due to crowdedness • competition for resources death rate = df * ( deaths = df * ( N K N K ) )*N Problems with simple logistic growth • births and deaths not separated • you might want to look at these processes separately • no age structure • age matters for reproduction % of Total Population Different populations can have different age structures Age % of Total Population Age structure affects reproduction growing rapidly not replacing itself- population is likely in decline window of reproduction Age The Tools of Population Ecology • • Modeling Creation of Life Tables Life Tables • • • Way of looking at age structure of population Trends and dynamics Provides quantitative information about: • life expectancy • proportion living • reproductive output Static vs. Cohort-based Life Tables • Static • analyze age structure of current population • assumes that one generation is similar to the next in terms of dynamics • Cohort-based (cohort= group) • follow a single generation through its entire lifespan • accurately describes the experience of that generation only Grasshopper Life Table Life stage # at start (nx) Proportion surviving at start (lx) Proportion dying in stage (dx) Mortality rate in stage (qx) Proportion alive in stage (Lx) Life expectancy (Ex) Egg 44,000 1.00 0.92 0.92 0.54 0.74 Inst. 1 3,513 0.08 0.02 0.28 0.07 2.55 Inst. 2 2,529 0.06 0.01 0.24 0.05 2.35 Inst. 3 1,922 0.04 0.01 0.24 0.04 1.94 Inst. 4 1,461 0.03 0.00 0.11 0.03 1.39 Adult 1,300 0.03 0.03 1.00 0.01 0.50 Opportunists vs. Competitors Do well in variable or unpredictable climate • High mortality • Population boom and bust cycles • Not very competitive • Rapid development • Early reproduction • Small body size • Single reproductive effort • Short lifespan • Do well with constant or predictable climate • Lower mortality • Population in equilibrium near carrying capacity • Very competitive • Slow development • Late reproduction • Large body size • Repeated reproduction • Longer lifespan • Survivorship Curves Competitors (K-selected) Large mammals, some plants Invertebrates, fish Opportunists (r-selected) (Life stage) Seasonal variation in life history • Daphnia retrocurva Spring morphology: Summer morphology: Round body, more eggs protective spikes, fewer eggs To avoid predation, natural selection favors a protective summer morphology that reduces egg production Why different life strategies? • • More ways to live in an environment and use its resources Another way to say this: filling niches What is a niche? • A niche is the total of all biotic and abiotic factors that determine how an organism fits into its environment. • Where and how does an organism live and function? • habitat • role in community