BIOL 4120 Principles of Ecology Lecture 13 Predation

BIOL 4120: Principles of Ecology Lecture 13: Predation Dafeng Hui Office: Harned Hall 320 Phone: 963 -5777 Email: dhui@tnstate. edu

Outline (chapter 14) 14. 1 Forms of Predation 14. 2 Mathematic model of predation 14. 3 Model suggests mutual population regulation 14. 4 Functional responses relate prey consumed to prey density 14. 5 Numerical response of predator to prey density 14. 6 Foraging decision making 14. 7 Foragers seek productive food patches 14. 8 Risk of predation can influence foraging behavior 14. 9 Coevolution can occur between predator and prey 14. 10 Animal prey have evolved defenses against predators 14. 11 Predators have evolved hunting tactics 14. 12 Plants and herbivores, carnivores interact

Predation Consumption of all or part of one living organism by another Prey Predator Functions: 1. Energy transfer 2. Predators are agents of mortality and feed on living organisms rather than scavengers or decomposers 3. Shape the community structure and evolution.

14. 1 Forms of Predation n Types of predation • Carnivory n Direct taking of animal prey for immediate consumption • Hawk taking a mouse • Herbivory n Consumption of plant material when plant is killed • Consumption of nuts and seeds • Parasitoidism n Predator lives in or on a host and eventually kills to provide a food source • Parasitic wasps • Parasitism n Predator lives in or on a host and consumes, but does not usually kill the host • Ticks on mammals • Cannibalism n Predation on same species (a special form) • Tadpoles in a pond

14. 2 Mathematical model for predation n n Lotka and Volterra equation for predation Prey n n Where c. Npred. Nprey is mortality of prey due to predator. c is per capita capture rate, and Npred, Nprey are the number of predators and prey, respectively. Predator n Where b is efficiency of conversion of prey consumed (c. Npred. Nprey) and d is death rate of predators

Solving the equations n For predator density (d. NPrey/dt=0) • Npred = r/c n n n 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 (d. NPred/dt=0) • Nprey = d/bc n n Growth rate of predator population is zero when rate of increase of prey is equal to rate of mortality divided by the product of b and c. Thus the two equations interact and this can be done graphically

Pred n n n 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

14. 3 Model suggests mutual population regulation n c. N_prey. N_pred: • For prey population, this term serves to regulate population growth through mortality • For predator population, it serves to regulate population growth through two distinct responses: Predator’s Functional responses: the great the number of prey, the more the predator eats. The relationship between per capita rate of consumption and the number of prey (c. Nprey. Npred). Predator’s Numerical response: an increase in consumption of prey results in an increase in predator reproduction (b(c. Nprey. Npred).

n n The Lotka–Volterra model is widely criticized for overemphasizing the mutual regulation of predator and prey populations • Still a valuable model Additional factors that influence predator–prey interactions • Cover or refuges for the prey • Difficulty of locating prey as it becomes scarcer • Choice among multiple prey species • Coevolution

14. 4 Functional Responses Relate Prey Consumed to Prey Density n n The functional response is the relationship between the per capita predation rate (number of prey consumed per unit time) and prey population size • This idea was introduced by M. E. Solomon in 1949 Three types of functional response (I, II, and III) • Developed by C. S. Holling

14. 4 Functional responses related prey consumed to prey density n Functional response • Ne=c. Nprey. Ts • Ts: period of search time • Ne: per capita rate of predation, i. e. , # of prey eaten during a given period of search time, Ts. • Type I functional response • Ne=c Nprey. Ts • Passive predator such as spider or the prey is less sufficiently abundant (e. g. , kestrels and voles) • All time allocated to feeding is searching.

n Type II response • Total time use include prey search and prey handling • T=Ts+(Th*Ne) • Replace Ts with T-Th*Ne and rearrange the equation, get: • Ne=c NPrey. T/(1+c Nprey. Th)

n Type II response • Ne=c NPrey. T/(1+c Nprey. Th) As prey # increase, Th*Ne increase, less time for prey search, decrease mortality rate of prey. this is the most commonly reported responses.

n Type III functional response • Sigmoid (S-shaped) response • At high prey density, the response is the same as type II response; however, the rate of prey consumed is low when the prey density is low at first, increasing in a S-shaped fashion. • • Factors caused the S-shape response 1. availability of cover to escape the predators 2. predator’s search image 3. Prey switching. Switch to other preys (more abundant)

Functional responses related prey consumed to prey density n Functional response • As prey increases, predators take more prey • But how n Linear • Rate of predation is constant n Decreasing rate to maximum • Rate of predation decline n Sigmoidal • Reaches maximum then declines (Right panel is expressed as proportion of prey density, # prey consumed divided by prey density)

n n n Linear Type 1 (European kestrel to vole) n Mortality of prey simply density dependent n No limits on system Decreasing Type 2 (weasel on rodent) n Predators can only eat so much – satiation n Time needed to kill and eat prey becomes limiting Sigmoid Type 3 (warbler on budworm larvae) n Capture rate is density dependent n Availability of cover n Alternative prey when preferred is rare (prey switching) n Prey not part of predators search image, not a desirable food source

Model of prey switching n Prey switching • Palatable versus less palatable • Better return per kill • Less energy needed to find and kill an abundant prey

14. 5 Predators respond numerically to changing prey density n Aggregative response in the redshank Numerical response • Predators reproduce more n However reproduction usually slower than prey • Movement into high prey density areas n This aggregative response is very important as it rapidly increases predator density

n Another example of numerical response • Bay-breasted Warbler • Spruce budworms

n Other numerical response as increased reproductive effort • • Weasels as predators Rodents as prey Predators followed prey in reproduction Increase of rodent was due to good harvest in 1990

14. 6 Foraging involves decisions regarding the allocation of time and energy n n Optimal foraging theory Hypothesis: natural selection should favor efficient foragers, those individuals that maximize their energy or nutrient intake per unit of effort. Foraging: what food to eat; where and how long to search; how to search. Costs and benefits • Cost: time and efforts on foraging • Benefit: survive and reproduce more, fitness

A simple model n n n n Two kinds of prey: P 1 and P 2 Energy yields: E 1 and E 2 Time required: Th 1 and Th 2 Profitability E 1/Th 1 and E 2/Th 2 If E 1/Th 1 > E 2/Th 2, then P 1 is more profitable: When a predator searches for P 1, but finds a P 2, should it eat it? What is a P 1 is nearby?

Optimal choice n n n Determined by search time Search time: Ts 1 and Ts 2 Eat P 2, profitability is E 2/Th 2 Search and eat P 1, E 1/(Ts 1+Th 1) If E 2/Th 2 is larger than E 1/(Ts 1+Th 1), then the predator should eat P 2

n Predators show prey preference • Optimum size for prey of wagtail is the middle prey length • Small one easy to handle, but E/Th is small. Wagtail

14. 8 Risk of predation can influence foraging behavior n Predator can be prey to other • Insects—birds—owls n n Balance energy gained against being eaten Avoid predator while foraging • Change foraging behavior (e. g. , time) • Change foraging site n from most profitable, but predator-prone site to a less profitable, but more secure part

14. 9 Coevolution can occur between predator and prey n n n Predators exert a selective pressure on prey — any characteristic that enables individual prey to avoid being detected and captured by a predator will increase its fitness Natural selection should • Function to preserve “smarter, ” more evasive prey • Produce “smarter, ” more skilled predators Coevolution: as prey species evolve ways to avoid being caught, predators evolve more effective means to capture them

14. 10 Animal prey have evolved defenses against predators n Predator defenses: characteristics that function to avoid detection, selection, and capture by predators • Chemical defenses n Pheromones to warn related species of attack • Fish n Poisons • Arthropods and fungi, snakes: example, stinkbug • Cryptic coloration (colors and patterns, object resemblance)) n Hide in normal environment • Moths on trees. Flounder • Flashing coloration n Distraction • Deer and rabbits, butterfly, grasshopper • Warning coloration or aposematism (bold colors with patterns that serve as warning to would-be predators) n Learnt behavior due to bad experience • Bees and wasps • Snake • Skunk (black and white stripes)

n Predator defenses (cont. ) • Mimicry n Copy coloration of toxic species • Batesian mimicry of tropical butterflies n Edible species mimic inedible species, nonvenomous mimic venomous species • Mullerian mimicry n Unrelated species have a shared color patterns that function to keep predators away n Snakes, social wasps • Armor n Difficult to kill • Clams, hedgehogs, armadillos • Behavorial defense n Grouping together • More difficult to attack a large herd, see African antelope • Timing of reproduction—predator satiation (cicadas)

Predator Defenses Cryptic coloration, warning coloration, Mullerian mimicry, Batesian mimicry, behavior defense

n Predator defenses fall into two classes: n Constitutive defenses • Fixed features of the organisms n n Object resemblance and warning coloration Induced defenses • Defenses are brought about or induced by the presence or action of predators n Chemical defense n Behavior defense

14. 11 Predators have evolved efficient hunting tactics n Hunting tactics • Ambush n n n Low success rate Low energy consumption Crocodiles, frogs, etc • Stalking n n n Long search time Short pursuit time Cats • Extreme example is cheetah • Pursuit n n n Know where prey is present so there is a short search time Long pursuit time Wolves, lions, hawks • Note this is a simplification n Stalking can involve ambush at water hole Pursuit can involve stalking if there is a large herd Cats can use ambush • Leopards up trees

n Predators may use cryptic coloration to blend into background and use deception by resemble the prey

14. 12 Herbivores prey on plants Amount of biomass eaten by herbivores: 6 -10% forest, 30 -50% grassland Outbreak of grasshopper, gypsy moths etc can kill http: //www. tnstate. edu/biology, chalktalk materials (Dr. Sam Mc. Naughton)

14. 13 Plants defend themselves from herbivores n Plants defend themselves • Chemical n Qualitative inhibitors • Poisons n Fungi Serve as call for helpers (corn, caterpillar, wasp) n Quantitative • Tannins reduce protein availability n Bushes in deserts • Structural n Thorns, spines, etc • Roses and Acacia n Note also carnivorous plants • Ambush strategy • Attractants

14. 14 Plants, herbivores, and carnivores interact n Complete interaction between plants, herbivores and carnivores

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14. 7 Foragers seek productive food patches n n Marginal value theorem: Predict the length of time an individual should stay in a resource patch before leaving and seeking another Length of stay is related to the richness of food patch (prey density), time require to travel (travel time t), and the time required to extract the resource. Optimal foraging theory predicts: predators should abandon the patch when the rate of return is at its maximum value, after which the rate of return begins to decline