# Ecology Lecture 10 Ralph Kirby. Predation Predators are agents of mortality and feed on living organisms rather than scavengers or decomposers Types of.

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Ecology Lecture 10 Ralph Kirby

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 Lotka and Volterra equation for predation Prey –dN prey /dt = rN prey – CN pred N prey Where CN pred N prey is mortality of prey due to predator. C is per capita capture rate and N pred N prey are the numbers of predators and prey respectively. Predator –dN pred /dt = B(CN pred N prey ) - DN pred Where B is efficiency of conversion of prey consumed (CN pred N prey ) and D is death rate of predators

Solving the equations For predator density –N pred = 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 –N prey = 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

Result is 3 rd 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

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

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

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

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

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

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

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

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

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 FungiQuantitative –Tannins reduce protein availability Bushes in deserts –Structural Thorns, spines, etc –Roses and Acacia Note also carnivorous plants –Ambush strategy –Attractants

Complete interaction between plants, herbivores and carnivores

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

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

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

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 in14 th century Smallpox in 18 th century Cholera in 19 th century AIDS in 21 st century? –Buffalo, wildebeest and cattle in Africa Rindepest in 19 th century

Note importance of population density –Black Death in14 th 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 18 th century Needs even high human population due to direct transmission Halted by human evolution –Vaccination –Cholera in 19 th century Needs even higher density and water/food transmitted Halted by human evolution –Clean water supply and bacteriology –AIDS in 21 st 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 19 th 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?

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

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

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

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

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