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ES 120 TOXICS IN THE ENVIRONMENT LECTURE 16-17: Effects on populations, communities and ecosystems SCOPE OF LECTURE • How can we recognize toxic effects on populations, communities and ecosystems? EFFECTS ON HIGHER LEVELS OF BIOLOGICAL ORGANIZATION • Population: group of individuals of same species in an area – Change in abundance – Change in age distribution – Change in genotypes • Community: group of populations in an area (see lecture on biomonitoring) • Ecosystem: interaction of biotic and abiotic factors in an environment 2 PARADIGMS OF POPULATION MODELS (CONTINUOUS) - Population growth rate is density independent and constant: Exponential growth: dN rN = dt - Population growth rate is density dependent, e.g.: Logistic growth: dN dt N) r N (1 = max K CONTINUOUS POPULATION GROWTH TOXICANT EFFECT ON LOGISTIC GROWTH WHY IT IS DIFFICULT TO DISCERN EFFECTS OF STRESS ON REAL POPULATIONS 1. There are multiple stressors, some density dependent and some density independent 2. Intensity of stressors varies in time 3. Population growth may be discrete 4. Real populations are age/size structured: birth and death rates depend on age/size 5. Dynamics of real populations depend on other species: competition, mutualism, parasitism, predation 6. A population may develop resistance to a stressor INTENSITY OF STRESSOR VARIES IN TIME: POPULATION OF BLUE HERONS DECLINES AFTER SEVERE WINTER DISCRETE POPULATION GROWTH MAY CAUSE FLUCTUTATIONS (LOGISTIC GROWTH) ‘PREDATOR-PREY’ DYNAMICS MAY LEAD TO FLUCTUATIONS Producer SUBLETHAL EFFECTS ON CONSUMER MAY INCREASE BOTH PRODUCER AND CONSUMER DENSITIES Consumer Producer ??? Consumer RESISTANCE IN INSECTS DEVELOPMENT OF RESISTANCE TO PYRETHROIDS IN COTTON BUD WORM (ANNUAL APPLICATION IN JANUARY/ FEBRUARY) EFFECTS ON HIGHER LEVELS OF BIOLOGICAL ORGANIZATION • Population: group of individuals of same species in an area • Community: group of populations in an area • Ecosystem: interaction of biotic and abiotic factors in an environment – Changes in elemental fluxes (C, N) MICROBIAL RESPIRATION IN SOILS AMMENDED WITH A HERBICIDE BIOMAGNIFICATION ACROSS TROPHIC LEVELS IN LAKE WASHINGTON (1 FULL TROPHIC LEVEL: d15N INCREASES 0.34%) DDT Predators Grazers Next Lecture • Linking toxic effects across biological levels of organizations • Review • Homework: – Read PE 15 – Study ‘Part 1’: PE 1 – 6 plus lecture material EXTRAPOLATION ACROSS LEVELS OF BIOLOGICAL ORGANIZATION • How can we relate the biochemical effects of pollutants to changes at the population level? Or: • How can we ‘proof’ that observed effects at higher levels of organization are caused by pollutants? THREE POSSIBLE APPROACHES 1. Apply mathematical models to translate effects at the biochemical level to population, community or ecosystem level • Methodology largely undeveloped 2. Conduct large scale mesocosm, field enclosure or field trials with varying pollutant levels including controls • Elaborate, time consuming, expensive 3. Use ‘mechanistic’ biomarkers with effects that are quantitatively ‘calibrated’ to population effects • Scope of chapter 15 FOUR EXAMPLES • Effects of organophosphorus pesticides on central nervous system • Effects of DDT on central nervous system • Effects of DDT on Ca-ATPase • Effects of synthetic estrogens on development ORGANOPHOSPHORUS INSECTICIDES BIOCHEMICAL INTERACTION OP inhibits Acetylcholine esterase Accumulation of Acetylcholine in synaptic cleft PHYSIOLOGICAL EFFECT EFFECTS ON INDIVIDUALS Continuing signal transduction leading to cramped muscles reduced feeding rates, escape from predators; death EFFECTS ON POPULATIONS increased mortality; reduced production EFFECT OF DDT ON CENTRAL NERVOUS SYSTEM (CNS) BIOCHEMICAL INTERACTION DDT inhibits Sodium channel in CNS Retarded restoration of Na/K gradient after passage of signal PHYSIOLOGICAL EFFECT EFFECTS ON INDIVIDUALS Disturbed signal transduction leading to tremors and convulsions reduced feeding rates, escape from predators; death EFFECTS ON POPULATIONS increased mortality; reduced production EFFECT OF DDT ON EGG SHELL PRODUCTION BIOCHEMICAL INTERACTION DDT inhibits CaATPase PHYSIOLOGICAL EFFECT Reduced transport of Ca over membrane in egg shell gland Reduction of egg shell thickness EFFECTS ON INDIVIDUALS EFFECTS ON POPULATIONS When thinning exceeds 17%, eggs may break Reduced breeding success SYNTHETIC ESTROGENS (EE2) BIOCHEMICAL INTERACTION EE2 binds to receptors of cells in various tissues PHYSIOLOGICAL EFFECT EFFECTS ON INDIVIDUALS Development of female secondary sexual characteristics; In liver of fish: production of vitellogenin Reduced sperm production male sterility EFFECTS ON POPULATIONS Reduction in recruitment ADDITIONAL REMARKS • Not all biomarkers indicate effects at higher levels of biological organization • Most sites are subject to multiple pollutants/ sources of stress, which obscure the clean relationship between a ‘mechanistic’ biomarker and effects on populations and beyond • Expression of biomarkers may depend on environmental conditions, season, time of day, etc