Ecology: Ecology Lecture 10 Ralph Kirby


Predation: Predation Predators are agents of mortality and feed on living organisms rather than scavengers or decomposers Types of predation Carnivory Direct taking of animal prey for immediate consumption Hawk taking a mouse Herbivory Consumption of plant material when plant is killed Consumption of nuts and seeds Parisitoidism Predator lives in or on a host and eventually kills to provide a food source Parasitic wasps Parisitism Predator lives in or on a host and consumes, but does not usually kill the host Ticks on mammals Cannabilism Predation on same species Tadpoles in a pond


Similar formula to describe predation as for competition: Similar formula to describe predation as for competition Lotka and Volterra equation for predation Prey dNprey/dt = rNprey – CNpredNprey Where CNpredNprey is mortality of prey due to predator. C is per capita capture rate and NpredNprey are the numbers of predators and prey respectively. Predator dNpred/dt = B(CNpredNprey) - DNpred Where B is efficiency of conversion of prey consumed (CNpredNprey) and D is death rate of predators


Solving the equations: Solving the equations For predator density Npred = r/C Growth rate of prey population is zero when density of predators equals per capita growth rate of prey divided by per capita capture rate of predators. Any increase in predator density will result in negative growth in prey population For prey density Nprey = D/BC Growth rate of predator population is zero when rate of increase of predators is equal to rate of mortality Thus the two equations interact and this can be done graphically


Slide5: Result is 3rd graph on left There is a cyclical rise and fall in both the predator and prey populations with time Density of predators lags behind density of prey Feast and Famine scenario Prey and predators are never quite driven to extinction Mutual population regulation Simplified analysis


Slide6: Excludes Availability of refuges Increased difficulty of finding rare prey Multiple prey species Predator preference among prey Coevolution Functional response As prey increases, predators take more prey But how Linear Rate of predation is constant Decreasing rate to maximum Rate of predation decline Sigmoidal Reaches maximum then declines


Slide7: Linear Type 1 Mortality of prey simply density dependent No limits on system Decreasing Type 2 Predators can only each so much – satiation Time needed to kill and eat prey becomes limiting Sigmoid Type 3 Capture rate is density dependent Availability of cover Alternative prey when preferred is rare Prey not part of predators search image, not a desirable food source


Slide8: Prey switching Palatable versus less palatable Better return per kill Less energy needed to find and kill an abundant prey Numerical response Predators reproduce more However reproduction usually slower than prey Movement into high prey density areas This aggressive response is very important as it rapidly increases predator density


Slide9: This is an example of an aggressive response Bay-breasted Warbler Spruce budworms


Slide10: Increased reproductive effort Weasels as predators Rodents as prey Predators followed prey in reproduction


Slide11: Coevolution Because of mutual interaction, there must be selection on both prey and predator Prey are better at escaping Predators that are better at capturing Note this is a moving target situation But there can be punctuation Prey defenses Chemical Pheromones to warn related species of attack Fish Poisons Arthropods and fungi Cryptic coloration Hide in normal environment Moths on trees. Melanism Flashing coloration Distraction Deer and rabbits Warning coloration Learnt behavior due to bad experience Bees and wasps Mimicry Copy coloration of toxic species Batesian mimicry of tropical butterflies Armor Difficult to kill Clams, hedgehogs Behavorial Grouping together More difficult to attach a large herd, see African antelope Timing of reproduction


Slide12: Hunting tactics Ambush Low success rate Low energy consumption Crocodiles, frogs, etc Stalking Long search time Short pursuit time Cats Extreme example is cheetah Pursuit Know where prey is present so there is a short search time Long pursuit time Wolves, lions, hawks Note this is a simplification Stalking can involve ambush at water hole Pursuit can involve stalking if there is a large herd Cats can use ambush Leopards up trees


Slide13: Each predator develops it own foraging strategy Extreme example is cheetah Very high speed High energy consumption Must have high success rate Failure has high price Robin Decides where to land and hunt Search for food items such as a worm Once located, food item is attacked and capture attempted When to call off capture if unsuccessful Energy balance Success return No success – look elsewhere


Slide14: Thus predators show prey preference Optimum size for pry of wagtail Note also that predator may be prey to another species Choice of hunt area becomes important Theoretically there is an optimum strategy for every predator But too many factor involved to identify this easily Note also that herbivory ideas put forward Plants defend themselves Chemical Qualitative Poisons Fungi Quantitative Tannins reduce protein availability Bushes in deserts Structural Thorns, spines, etc Roses and Acacia Note also carnivorous plants Ambush strategy Attractants


Slide15: Complete interaction between plants, herbivores and carnivores


Slide16: Parasitism Predation Negative effect Do not usually kill host Eco- and Endo- parasites Wide variety of access routes Microparasites Viruses, bacteria, fungi, protozoa etc May cause disease Usually direct transmission Air, water, etc Macroparastites Liverflukes, ticks, mistletoe, etc Usually more than one host Both direct and indirect transmission Latter involves a vector such as a mosquito for malaria Commensalism Obligatory Minimization of negative effects Mutualism Advantage to both


Slide17: Life cycle can become complex as with meningeal worm and white tailed deer Definitive host Where adult stage reproduces Intermediate hosts Where juvenile stages grow


Slide18: Host response to parasite Avoidance Grooming Inflammatory response in animals Gall formation in plants Immune response in animals Vaccination Parasite adaptation Malaria


Slide19: Parasites affect host survival and reproduction Malaria in humans Can end up with balance Malaria in humans Sickle-cell anemia in Africans Parasites can be major regulators of population Humans Black Death in14th century Smallpox in 18th century Cholera in 19th century AIDS in 21st century? Buffalo, wildebeest and cattle in Africa Rindepest in 19th century


Slide20: Note importance of population density Black Death in14th century Needs lots of rats and some concentration of human population Not a major problem to Romans or Chinese civilizations due to good urban planning Smallpox in 18th century Needs even high human population due to direct transmission Halted by human evolution Vaccination Cholera in 19th century Needs even higher density and water/food transmitted Halted by human evolution Clean water supply and bacteriology AIDS in 21st century Needs even higher population density Never a problem in low density central African origin except to some villages Sexual transmission requires large number of contact, cf syphilis in 19th century Major effect on population once infection rate reaches 2%-5% Exponential growth in southern Africa Affects human productivity directly Halted by Change in human behavior? Science?


Slide21: Parasitism can evolve into mutualism Symbiotic or none symbiotic At least one pair becomes totally dependent on the other Ruminants stomach and microorganisms to digest plant material Rhizobium and nitrogen fixation in legumes Frankia and nitrogen fixation in some woody plants Endomycorrhizae and plant roots Lichens Mitochondria Chloroplasts


Slide22: When things get so involved they cannot be separated 2.5 billion year host guests


Slide23: Mutalism can be none symbiotic Pollination Seed dispersal Multiple species may be involved


Slide24: Mutualism can involve multiple species and affect the community Oaks Truffles Voles Pigs Humans Humans Humans use trained pigs to find truffles Human eat truffles Human keep oak forests to harvest truffles Voles spread truffle spores Oaks need truffle mycorrhizae Truffle farms in Australia without voles need human innoculation of oaks