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Biodiversity and Conservation: Extinctions The gradual process of becoming extinct is known as background extinction. Mass extinctions: When a large percentage of all living species become extinct in a relatively short period of time. 250 MYA: Over 90% of species died EXTINCTION RATES Biodiversity and Conservation: Extinctions ESTIMATED NUMBER OF EXTINCTIONS SINCE 1600 Group Mainland Island Ocean Total Approximate Number of Species Percent of Group Extinct Mammals 30 51 4 85 4000 2.1 Birds 21 92 0 113 9000 1.3 Reptiles 1 20 0 21 6300 0.3 Amphibians 2 0 0 2 4200 0.05 Fish 22 1 0 23 19,100 0.1 Invertebrates 49 48 1 98 1,000,000+ 0.01 Flowering Plants 245 139 0 384 250,000 0.2 Biodiversity and Conservation: Extinctions Cretaceous Period (65 MYA) Triassic Period (200 MYA) Permian Period (250 MYA) FIVE MOST RECENT MASS Devonian Period (360 MYA) EXTINCTIONS Ordovician Period (444 MYA) LIMITS TO GROWTH Copyright Pearson Prentice Hall Population Ecology: Population Growth Rate Population growth models Limits to exponential growth Population Density (the number of individuals per unit of land area or water volume) increases as well Competition follows as nutrients and resources are used up The limit to population size that a particular environment can support is called carrying capacity (k) POPULATION LIMITING FACTORS A limiting nutrient is an example of a more general ecological concept: a limiting factor. In the context of populations, a limiting factor is a factor that causes population growth to decrease. LIMITING FACTORS Copyright Pearson Prentice Hall Population sizes are controlled by various interactions among organisms that share a community. Predation and competition are two interactions that control populations. ORGANISM INTERACTIONS Limiting Factors The primary productivity of an ecosystem can be reduced when there is an insufficient supply of a particular nutrient. Ecologists nutrients. call such substances limiting LIMITING FACTORS Copyright Pearson Prentice Hall POPULATION DENSITY Let’s say our classroom is 600 sq. ft. In 3rd hour and fifth hour, there are 25 students in the class. The population density for 3rd and 5fth hour is 25 students/600 ft² or .04 students/ft². In 6th hour, there are only 19 students in the class. Is the population density higher or lower? SIX NEW STUDENTS WERE ADDED TO SIXTH HOUR. THE POPULATION DENSITIES OF ALL THE CLASSES IS NOW THE SAME. THE SCHOOL IS SPONSORING AN EVENT THAT ALLOWS STUDENTS TO MISS 3RD, 5TH, AND 6TH HOURS. WHICH CLASSES WILL BE MOST EFFECTED? All equally effected! The event will disrupt class regardless of size – everyone will have the opportunity to go. ITS FLU SEASON, AND LOTS OF SICK STUDENTS ARE COMING TO SCHOOL. THEY ARE COUGHING, SNEEZING, AND TOUCHING EVERYTHING. TEN PERCENT OF MS. SONLEITNER’S STUDENTS HAVE THE FLU, BUT ARE SO DEDICATED THEY COME TO CLASS ANYWAY. IF MS. SONLEITNER WIPES DOWN EVERY TABLE BEFORE EVERY CLASS, WHICH CLASS WILL BE MOST AFFECTED BY THE FLU? 3rd and 5th hours, because they have the greatest population density. A larger number of students will be infected and have opportunity to infect a larger number of healthy students. POPULATION CHARACTERISTICS 1. Population Density: 2. The number of organisms per unit area Spatial Distribution: Dispersion: The pattern of spacing a population within an area 3 main types of dispersion Clumped Uniform Random The primary cause of dispersion is resource availability Population dynamics – study of how characteristics of a population changes in response to changes in the environmental conditions Populations differ in Distribution Numbers Age structure POPULATIONS HAVE CERTAIN CHARACTERISTICS Random Independent of other organisms No DISTRIBUTION PATTERNS habitat preference Uniform Even spacing Evidence DISTRIBUTION PATTERNS for intraspecific competition (among other sea otters) Clumped Organisms tend to be together Habitat preference Behavioral DISTRIBUTION PATTERNS preference such as herding Most common! WHY CLUMPING? Species tend to cluster where resources are available Protects some animals from predators Packs allow some to get prey Temporary groups for mating and caring for young deer population dynamics What is happening to this population? 20 number of deer 18 16 14 12 10 8 6 4 2 0 0 Why doesn’t the population ever go above 18? 2 4 6 8 Year 10 12 14 deer population dynamics 20 number of deer 18 16 Why does population increase? 14 12 10 8 6 4 2 0 0 2 4 6 8 Year 10 12 14 CROWDING As populations increase in size in environments that cannot support increased numbers, individual animals can exhibit a variety of stress symptoms. • These include aggression, decrease in parental care, decreased fertility, and decreased resistance to disease. • They become limiting factors for growth and keep populations below carrying capacity. Carrying Capacity The number of organisms of one species that an environment can support indefinitely. 18 is the Carrying Capacity for our population. 3. Population growth rate How fast a given population grows Factors that influence this are: Natality ( Birth rate) Mortality (Death rate) Emigration (the number of individuals moving Away from a population) Immigration (the number of individuals into a population) POPULATION LIMITING FACTORS POPULATION LIMITING FACTORS Population growth models Logistic Growth Model Often called the S-shaped growth curve Occurs when a population’s growth slows or stops following exponential growth. Growth stops at the population’s carrying capacity Populations stop increasing when: Birth rate is less than death rate (Birth rate < Death rate) Emigration exceeds Immigration (Emigration > Immigration) POPULATION GROWTH • An increase in the number of individuals in a population Unlimited resources and reproduction lead to population growth (G) Growth = Births – Deaths (G = B – D) Cohort --- all the members of a population born at the same time. Survivorship---the probability of newborn individuals of a cohort surviving to particular ages. Illustrated by Survivorship Curves MORTALITY PATTERNS When births exceed deaths you see population growth. 600 500 J-Shaped Curve 400 300 Series1 POPULATION GROWTH 200 100 0 0 2 4 6 8 10 12 • Exponential growth means that as a population gets larger, it also grows at a faster rate. 600 500 J-Shaped Curve 400 300 Series1 200 EXPONENTIAL GROWTH 100 0 0 2 4 6 8 10 12 Put your pens down for a minute & think about this: An employer offers you two equal jobs for one hour each day for fourteen days. The first pays $10 an hour. The second pays only 1 cent a day, but the rate doubles each day. Which job will you accept? UNDERSTANDING EXPONENTIALS Population Ecology: Population Growth Rate Job 1 Job 2 90 80 Now, how much would your employer 70 owe you if you 60 stayed at this job for another 2 weeks? 50 Job 2 lags for a long time before 40 What would happen if exponential this type of growth took 30 growth kicks in! place within a 20 UNDERSTANDING EXPONENTIALS population? 10 0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 Scope of Ecology Population Density and Distribution Population Growth Models Survivorship Curves Age Distributions Regulation of Population Size Life History Patterns Human Population Growth Environmental Impact Logistic growth—indicated by an S-shaped curve Difference between logistic and exponential due to environmental resistance LOGISTIC GROWTH LOGISTIC GROWTH St. Paul Island Reindeer Population Deaths begin to exceed births and the population falls below carrying capacity population growth over 20 years 600 S - Curve population 500 400 300 200 100 0 0 2 4 6 8 10 year 12 14 16 18 20 POPULATION LIMITING FACTORS Population growth models Logistic Growth Model The S-curve is not as pretty as the image looks 1. Carrying capacity can be raised or lowered. How? Example 1: Artificial fertilizers have raised k Example 2: Decreased habitat can lower k 2. Populations don’t reach k as smoothly as in the logistic graph. • Boom-and-Bust Cycles • Predator-Prey Cycles SURVIVORSHIP CURVES SURVIVORSHIP CURVES THE HUMAN POPULATION doubled three times in the last three centuries about 6.1 billion and may reach 9.3 billion by the year 2050 improved health and technology have lowered death rates The history of human population growth Figure 35.8A The age structure of a population is the proportion of individuals in different age-groups RAPID GROWTH SLOW GROWTH ZERO GROWTH/DECREASE Kenya United States Italy Male Female Male Female Ages 45+ Ages 45+ Ages 15–44 Ages 15–44 Under 15 Percent of population Male Female Under 15 Percent of population Percent of population Also reveals social conditions, status of women Figure 35.9B Rapid life-history patterns are common among organisms from changeable or unpredictable environments. REPRODUCTION PATTERNS: 20 MINUTES! RAPID LIFE-HISTORY PATTERNS Large species that live in more stable environments usually have slow life-history patterns. 22 MONTHS! REPRODUCTION PATTERNS: SLOW LIFE-HISTORY PATTERNS • Reproduce and mature slowly, and are longlived. • Maintain population sizes at or near carrying capacity. GROWTH LIMITATIONS When a population overshoots the carrying capacity, then limiting factors may come into effect. Resources Disease Organism interaction Habitat Size/Crowding Weather TWO TYPES OF LIMITING FACTORS: Density-dependent and Density-independent Population density describes the number of individuals in a given area. DENSITY-INDEPENDENT FACTORS Density-Independent Factors Density-independent limiting factors affect all populations in similar ways, regardless of the population size. Copyright Pearson Prentice Hall Population Ecology: Density-independent factors Density-independent These factors are usually abiotic factors They include natural phenomena, such as weather events Drought, flooding, extreme heat or cold, tornadoes, hurricanes, fires, etc. POPULATION LIMITING FACTORS Density-independent factors can affect all populations, regardless of their density. Most density-independent factors are abiotic factors, such as temperature, storms, floods, drought, and major habitat disruption DENSITY - INDEPENDENT DENSITY-INDEPENDENT FACTORS Examples of density-independent limiting factors include: unusual weather natural disasters seasonal cycles •Example: Deer foraging for food in deep snow during the winter. certain human activities—such as damming rivers and clearcutting forests Copyright Pearson Prentice Hall DENSITY-DEPENDENT FACTORS Density-dependent competition predation parasitism disease Copyright Pearson Prentice Hall limiting factors include: Density-dependent factors include disease, competition, predators, parasites, and food. Disease, for example, can spread more quickly in a population with members that live close together. DENSITY - DEPENDENT Density-dependent factors exist only when the population density reaches a certain level. These factors exist most strongly when a population is large and dense. They do not affect small, scattered populations as greatly. Copyright Pearson Prentice Hall COMPETITION • Is Density - Dependent When only a few individuals compete for resources, no problem arises. • When a population increases to the point at which demand for resources exceeds the supply, the population size decreases. Positive and negative interactions Predation Interspecific competition Competition is an interaction between individuals of the same or of different species membership, in which the fitness of one is lowered by the presence of the other. Herbivory is a form of parasitism Symbiosis is any type of relationship where two individuals live together Amensalism is a relationship between individuals where some individuals are inhibited and others are unaffected. Parasitism is any relationship between two individuals in which one member benefits while the other is harmed but not killed or not allowed to reproduce. Parasitoidism is a relationship between two individuals in which one member benefits while the other is not allowed to reproduce or to develop further Commensalism is a relationship between two individuals where one benefits and the other is not significantly affected. Mutualism is any relationship between two individuals of different species where both Mutualism is the way two organisms of different species exist in a relationship in which each individual benefits. Mutualism is the oposite to interspecific competition. Client– service relationships Pollination Mutualism is often linked to coevolutionary processes Facilitation is a special form of commensalism and describes a temporal relationship between two or more species where one species benefits from the prior (and recent) presence of others. In plant succession early arriving plants pave the way for later arrviing by modifying soil condition. Intraspecific competition Canis lupus Mytilus edulis Scramble (exploitation, diffuse) is a type of competition in which limited resources within an habitat result in decreased survival rates for all competitors. Contest (interference) competition is a form of competition where there is a winner and a loser Mate competition Territoriality 𝜎2 ≪ 𝜇 The variance in distance is much less than the mean distance Territories imply a more or less even distribution of individuals in space Territoriality is a form of avoidance of intraspecific competition Overlap Territory Home range Home ranges might overlap Home range Territory Competition When populations become crowded, organisms compete for food, water space, sunlight, and other essential resources. Competition among members of the same species is a density-dependent limiting factor. Copyright Pearson Prentice Hall Competition can also occur between members of different species. This type of competition can lead to evolutionary change. Over time, the species may evolve to occupy different niches to avoid competition. DENSITY-DEPENDENT FACTORS Copyright Pearson Prentice Hall Predation Populations in nature are often controlled by predation. The regulation of a population by predation takes place within a predatorprey relationship, one of the best-known mechanisms of population control. DENSITY-DEPENDENT FACTORS Predators may capture prey by: Walking Swimming Flying Pursuit and ambush Camouflage Chemical warfare MOST CONSUMER SPECIES FEED ON LIVE ORGANISMS OF OTHER SPECIES PREDATION Populations of predators and their prey experience cycles or changes in their numbers over periods of time. Lynx and Hare pelts sold to the Hudson’s Bay Company Wolf and Moose Populations on Isle Royale DENSITY-DEPENDENT FACTORS Moose Copyright Pearson Prentice Hall Wolves Predation Erigone atra Canada lynx and snowshoe hare Specialist predator Generalist predator Oligophages Polyphages Monophages Prey quality Stoppin g point Starvation Maximu m yield Trade-offs in foraging Animals should adopt a strategy to maximuze yield Optimal foraging theoryforaging Holling’s optimal theory 𝐹𝑜𝑜𝑑 𝑖𝑛𝑡𝑎𝑘𝑒 ∝ 𝐷𝑒𝑛𝑠𝑖𝑡𝑦𝑓𝑜𝑜𝑑 𝑡𝑡𝑟𝑎𝑣𝑒𝑙 1 + 𝑎𝐷𝑒𝑛𝑠𝑖𝑡𝑦𝑓𝑜𝑜𝑑 𝑡ℎ𝑎𝑛𝑑𝑙𝑖𝑛𝑔 Searching time Great tits forage at site of different quality How long should a bird visit each site to have optimal yield? 1 0 2 0 1 5 3 1 8 1 1 4 1 7 Parus major 8 9 Predicted energy intake from travel and handling time Predicted energy intake from travel time Cowie 1977 Specialist predators and the respective prey often show cyclic population variability 12 year Cycles of the cycle predator follow that of the prey Canada lynx and snowshoe hare Hudson’s Bay Company Data from MacLulick 1937, Univ. Toronto Studies, Biol. Series 43 Data from Yoshida et al. 2003, Nature 424 Bracyonus calyciflorus Chlorell a vulgaris Cycles might be triggered by the internal dynamics of the predator – prey interactions or by external clocks that is environmental factors of regular appeareance Most important are regular climatic variations like El Nino, La Nina, NAO. The Lotka Volterra approach to specialist predators e: mortality rate of the predator 𝑑𝑃 𝑑𝑁 𝑑𝑃 = −𝑒𝑁 = 𝑟𝑁 − 𝑎𝑃𝑁 = 𝑓𝑎𝑁𝑃 − 𝑒𝑃 r: reproductive rate of the prey 𝑑𝑡 𝑑𝑡 𝑑𝑡 faN: reproductive rate of the predator 𝑑𝑁 𝑟 𝑑𝑃 𝑒 f: predator efficieny =0→𝑃= =0→𝑁= 𝑑𝑡 𝑎 𝑑𝑡 𝑓𝑎 aP: mortality rate of the prey The equilibrium abundances of prey and a: attack rate predator In nature most predator prey relationships are more or less stable. The Lotka Volterra models predicts unstable delayed density dependent cycling of populations Any deviation from the assumption of the Lotka Volterra model tends to stabilize population: • Prey aggregration • Density dependent consumption • Functional responses Variability, chaos and predator prey fluctuations 𝑑𝑁 𝑑𝑃 = 𝑟𝑁 − 𝑎𝑃𝑁 = 𝑓𝑎𝑁𝑃 − 𝑒𝑃 𝑑𝑡 𝑑𝑡 Lotka Volterra cycles with fixed parameters a, e, f, r. Lotka Volterra cycles with randomly fluctuating parameters tends a, e, f,tor. Stochasticity stabilize populations Dynamic equilibrium Any factor that provides not too extreme variability into parameters of the predator prey interaction tends to stabilize populations. Fixed parameter values cause fast extinction. Herbivory Feeding Strategy Diet Example Frugivores Fruit Ruffed lemurs Folivores Leaves Koalas Nectarivores Nectar Hummingbirds Granivores Seeds Hawaiian Honeycreepers Palynivores Pollen Bees Mucivores Plant fluids, i.e. sap Aphids Xylophages Plant defenses Wood against herbivors Termites Many plants produce secondary metabolites, known as allelochemicals, that influence the behavior, growth, or survival of herbivores. These chemical defenses can act as repellents or toxins to herbivores, or reduce plant digestibility. Alcaloide (amino acid derivatives): nicotine, caffeine, morphine, colchicine, ergolines, strych nine, and quinine Terpenoide, Flavonoids, Tannins Mechanical defenses: thorns, trichomes… Mimicry Mutualism: Ant attendance, spider attendance Digitalis Negative feedback loops occur when grazing is too low Reduced structural complexit y Low coral cover Decreasing coral recruitment Hay and Rasher (2010) Decreasin g fish recruitme nt Low grazing intensity Increasing algal cover Functions of herbivores in coral reefs Herbivorous fish (Diadema) Positive feedback loops occur when grazing is high Increased structural complexity High coral cover Overfishing of Increasing herbivorous fish coral might cause a shift recruitment to algal dominated low divesity Increasin g fish recruitme nt High grazing intensity Decreasing algal cover Parasitism and Disease Parasites can limit the growth of a population. A parasite lives in or on another organism (the host) and consequently harms it. Copyright Pearson Prentice Hall A limiting factor that depends on population size is called a densitydependent limiting factor . Density-Dependent Factors Copyright Pearson Prentice Hall Population of New Orleans, La 1970-2006 650000 population 550000 450000 350000 250000 150000 50000 -500001968 1973 1978 1983 1988 1993 1998 year 1. What are the independent and dependent variables? 2. What is the population trend? 3. Why did this happen? Is this densitydependent or independent? 2003 2008 Global population 1900 - 2046 Population in Billions 10 9 8 7 6 recorded population 5 projected population 4 3 2 1 0 1850 1900 1950 2000 2050 2100 Years 4. What type of growth is this? 5. When does growth increase? What might have happened to cause this? PREDATOR-PREY INTERACTIONS: LECTURE CONTENT Predator-prey interactions often dramatic, illustrated by snowshoe hare-lynx population fluctuations Simple Lotka-Volterra predator-prey model generates fluctuations of prey, predator Graphical models identify factors that stabilize, destabilize predator-prey interaction Importance of predation in nature attested to by various lines of evidence Diversity, ubiquity of anti-predator adaptations Evidence that predators control prey, under particular conditions Impact of interacting predators and prey in population cycles PREDATOR-PREY INTERACTIONS ARE OFTEN DRAMATIC-- “NATURE RED IN TOOTH AND CLAW”--AS ILLUSTRATED BY THIS LION ABOUT TO SNAG A HYENA ONE OF THE MOST FAMOUS EXAMPLES OF PREDATOR-PREY INTERACTIONS ILLUSTRATED BY CANADA LYNX AND SNOWSHOE HARE, IN CANADIAN TAIGA (FOREST) BIOME DRAMATIC FLUCTUATIONS OF HARE AND LYNX POPULATIONS Note regular periodicity, and lag by lynx population peaks just after hare peaks HARE-LYNX EXAMPLE Charles Elton’s paper (1924), “Periodic fluctuations In the numbers of animals: their causes and effects”, British Journal of Experimental Biology, was first (of MANY) publications to analyze this data set Are these cycles regular, i.e., with constant periodicity? What causes these cycles? Interaction of predator and prey? Hare-resource interaction? (hares feed on fir tree needles, and other vegetation) Sunspot Humans cycles? (as hunters) interacting with both predator and prey? MODELING IS ONE WAY ECOLOGISTS HAVE STUDIED PREDATOR-PREY POPULATION DYNAMICS Lotka-Volterra Predator-Prey model is the classic model (see “Summary: Lotka-Volterra PredatorPrey Model”, lecture notes on web page) This model generates highly regular oscillations of both prey and predator population fluctuations, as seen in hare-lynx data (see next slide) However, this model results in “neutral stability”, a very fragile kind of stability that does not explain the factors that tend either to stabilize or destabilize population dynamics of predator-prey interactions To appreciate stabilizing, destabilizing influences on predator-prey systems, we will use graphical analysis PREDATOR-PREY POPULATION FLUCTUATIONS (NEUTRAL STABILITY) IN LOTKA-VOLTERRA MODEL GRAPHICAL ANALYSES AND STABILITY OF PREDATOR-PREY SYSTEMS Modifications of prey isocline (see lecture, text) Humped prey isocline Why is it often hump-shaped? (Recall slope of logistic model) Allee effect at low prey densities Stability depends on relative position of predator isocline Prey refuge from predator Modifications of predator isocline Predator carrying capacity Predator interference (e.g., territoriality) Factors that destabilize predator-prey interactions Time lags, predator efficiency Monophagous predator (inability to switch prey) WHAT EVIDENCE THAT PREDATORS ARE AN IMPORTANT FACTOR IN NATURE? Diversity, ubiquity of antipredator adaptations in many kinds of prey Impact of predators on prey populations Reviews Role of literature of predators in oscillating populations of prey and predators SOME ANTI-PREDATOR ADAPTATIONS IN INSECTS (AND A FEW VERTEBRATES) Warning = aposematic coloration Batesian mimicry--palatable mimic Mullerian mimicry--both Camouflage, model and mimic unpalatable crypsis--match background, unpalatable object Catalepsis--frozen posture Aggression, of unpalatable model with appendages retracted counter-attack (bombadier beetle) Aggression--e.g., stinging, biting such Armor--spines, as wasps & bees thorns, anti-swallowing devices, large size, bluffing Masting--synchronous reproduction (e.g., Escape 13- ,17-year cicadas) behaviors--e.g., jumping Homoptera Prey may avoid capture by Camouflage Chemical Warning warfare coloration Mimicry Deceptive looks Deceptive behavior MOST CONSUMER SPECIES FEED ON LIVE ORGANISMS OF OTHER SPECIES PREY DEFENSES Predation usually results in the evolution of defensive adaptations in prey. These can include: Chemical defenses (toxins, poison, acrid sprays) Behavior (living in groups, scouts, alarm calls) Morphological features (spines, color, structures that allow you to run fast or detect predators), and other traits Photo Credit: Rhett A. Butler @ mongabay.com Caterpillar with Venomous Spines Caterpillar Video: http://www.youtube.com/watch?v=oWOC8trquFo BEHAVIORAL DEFENSE EXAMPLE APOSEMATIC COLORATION IN POISON-ARROW FROG, MONTEVERDE, COSTA RICA (PHOTO BY T.W. SHERRY & T.K. WERNER) BATESIAN MIMICRY OF WASP (UNPALATABLE MODEL, UPPER LEFT) BY (1) MANTISPID (NEUROPTERA, PALATABLE MIMIC, UPPER RIGHT), AND (2) MOTH (PALATABLE MIMIC, LOWER); (RICKLEFS 2001) MULLERIAN MIMICRY IN TWO PAIRS OF BUTTERFLIES (RICKLEFS 2001) (HELICONIINAE) CRYPTIC COLORATION IN COSTA RICAN MOTH (CENTER OF PHOTO) RESTING ON GROUND DURING DAY (PHOTO BY T.W. SHERRY) CRYPTIC (LEAF-LIKE) COLORATION IN CHOERADODIS RHOMBICOLIS MANTID, COSTA RICA VENTRAL VIEW OF CHOERADODIS RHOMBICOLIS MANTID, COSTA RICA: PROTHORACIC FLAP (SHIELD-LIKE STRUCTURE JUST BEHIND HEAD) CAUSES 10-FOLD INCREASE IN HANDLING TIME BY COSTA RICAN NUNBIRDS (LARGEINSECT PREDATOR), BASED ON EXPERIMENT BY T. SHERRY (PHOTO BY T. CATALEPSIS IN COSTA RICAN KATYDIDS: SEE TWO INSECTS ALONG LEAF VEINS (ARROWS), WITH ONLY ONE PAIR OF LEGS PROTRUDING OUT OF ALLIGNMENT WITH REST OF BODY (PHOTO BY T.W. SHERRY) BOMBADIER BEETLE (BRADINUS CREPITANS) SPRAYING BOILING HOT ACID AT PREDATOR; NOTE ALSO APOSEMATIC COLORATION (PHOTO BY THOMAS EISNER, CORNELL UNIVERSITY) ACTIVE DEFENSE--URTICATING (STINGING) CATERPILLAR IN COSTA RICA (PHOTO BY T.W. SHERRY & T.K. WERNER) PINNED SPECIMENS OF JUMPING HOMOPTERA FROM COSTA RICA (SUPERFAMILY FULGOROIDEA)--NOTE LARGE HIND-LEGS (PHOTO BY T.W. SHERRY) SOME CONCLUSIONS FROM EXAMPLES OF ANTI-PREDATOR ADAPTATIONS Diversity, ubiquity of anti-predator adaptations attests to intense selection pressure by predators Some adaptations are subtle, poorly studied to date (e.g., large body size as a refuge, anti-predator flaps) Many prey have multiple adaptations, weapons Tropics (and deep oceans) are arenas for intense predator-prey coevolution (long time periods of stable environments, specialized adaptations in relatively constant environments, yearlong activity, diverse predators, prey) Anti-predator adaptations are one form of evidence for the impact of predators in ecological systems IMPACT OF PREDATION ON BULLFROG TADPOLE BEHAVIOR AND GROWTH RATE (FROM RICKLEFS 2001) BIRDS AS PREDATORS ON CATERPILLARS IN THE HUBBARD BROOK EXPERIMENTAL FOREST, NH (HOLMES, SCHULTZ, AND NOTHNAGLE, 1972); ASTERISKS INDICATE SIGNIFICANT DIFFERENCES OTHER EXAMPLES OF PREY CONTROL BY PREDATOR Dingo (wild dog) introduced into Australia has huge impact on several herbivores there: kangaroos, emus, feral pigs Populations of all these animals significantly reduced where dingos live (prey eliminated in some areas) Feral pigs have different population age-structure where dingos present versus absent (see text) Sea otters control abundance of sea urchins, sea urchins of kelp beds (& orcas of sea otters!) Review by Andrew Sih (1985): 95% of studies showed some effect of predation; 85% large effect Introduced predators have disproportionate effect WHAT IS ROLE OF PREDATORS IN CAUSING OSCILLATIONS OF PREDATOR, PREY? Look at case study, of lynx-hare system Krebs et al. (1996) study in arctic Canada Winter food known to be important: Food quality declines when heavily grazed at high hare density Study attempted to get at both factors by reducing predators (using exclosures) & supplementing food (rabbit chow) during a population peak and subsequent decline Next three slides present some of results of their study ABUNDANCE OF HARE POPULATIONS IN RESPONSE TO TREATMENTS AND CONTROLS, DURING POPULATION PEAK, & SUBSEQUENT DECLINE (KREBS ET AL.) RATIO OF DENSITY OF HARES IN TREATMENT VERSUS CONTROLS FOR SEPARATE AND COMBINED TREATMENT EFFECTS; NOTE BY FAR THE GREATEST EFFECT OF COMBINED TREATMENTS (C) SURVIVAL RATES OF HARES ALSO SHOW MUCH GREATER IMPACT OF COMBINED TREATMENTS CONCLUSIONS FROM KREBS ET AL. EXPERIMENT ON LYNX-HARE POPULATION OSCILLATIONS: It was possible to prolong peak of population abundance of hares, but difficult! Both food additions and predator reductions affected hare populations separately Effect of both food and predators had greatest overall effect, indicating an interaction of food and predators on prolonging hare population at high level SOME HUMAN APPLICATIONS OF PREDATOR-PREY MODELS Humans as super-efficient predator that destabilizes predator-prey interactions (e.g., fisheries) Humped catch-yield versus fishing effort curve in some fisheries How does increased predator efficiency destabilize? Interaction with natural environmental instability (e.g., El Niño-La Niña climate fluctuations) Introductions of predators often tend to destabilize predator-prey systems….why? CONCLUSIONS: Predator-prey conspicuous ecological interactions often dramatic, Models help identify factors that stabilize and destabilize predator-prey interactions Classic Lotka-Volterra model leads to oscillations, but neutral stability Stabilizing factors--prey self-limitation, prey refuge, spatial heterogeneity, predator territoriality De-stabilizing factors--predator more efficient, time-lags Importance of predators in nature supported by experiments on predator-impacts, anti-predator adaptations, impact of predators on population oscillations, activities of humans HERBIVORE-PLANT INTERACTIONS An herbivore grazing on a plant is another example of predation. Usually, only part of the prey is eaten by the predator. Photo Credit: Rhett A. Butler @ mongabay.com