4. 1 Species interactions- 1

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Species Interactions Section 10 D 1


Why are ecological interactions important? Affect distribution and abundance. Cause developmental change over time. Impact strategies in survival. Interactions can influence evolution 2

Two types of species interactions:

Two types of species interactions 3 1) Intraspecific interaction 2) Interspecific interaction


Types…. Type of interaction Intraspecific Interspecific Use of same limiting resource Competition Competition Consumption of all or part of another individual Cannibalism Predation Individuals live in close association, with mutual benefit Mutualism Mutualism Individuals live in close association , at the cost of host Parasitism Parasitism 4

Species interaction affect on each other:

Species interaction affect on each other Type of interaction Effect on species A Effect on species B Competition -- -- Predation + -- Parasitism + -- Neutralism 0 0 Amensualism 0 - Commensualism 0 + ‘0’ is no effect, ‘+’ is beneficial, ‘-’ is detrimental 5


COMPETITION Mutual use of a limited resource by populations of two or more species. Each individual adversely affect another in the quest for food (nutrients), living space, mates, or other common needs. Individuals can harm one another is attempting to gain a resource. Leading to a reduction in survivorship, growth, and/or reproduction of the individuals concerned. Abundance of both is greater when alone, than when together. May cause the development of different niches or physical characteristics. 6


COMPETITION May be: interspecific , or intraspecific Due to: exploitation, or interference Result in: mutual extinction, or exclusion of one, or coexistence 7

Ways in which competition operates:

Ways in which competition operates Exploitation This occurs indirectly through a common limiting resource which acts as an intermediate. Consumptive : consuming shared resources Pre-emptive : using space Overgrowth : Plants over shade other plants Observed in canopy of taller trees 8

Ways in which competition operates:

Interference This occurs directly between individuals via aggression etc. when the individuals interfere with foraging, survival, reproduction of others, or by directly preventing their physical establishment in a portion of the habitat. Chemical interference by Allelopathy Encounter : transient interactions directly over a specific resource. Territorial: behavior or fighting in defense of space Ways in which competition operates Observed in male-male competition in red deer during rut 9

Categories of Competition:

Categories of Competition When competition is between individuals of: ---- same species (intraspecific) ---- different species (interspecific) 10

Intraspecific competition :

Intraspecific competition 11 Competition occurring between members of the same species. Regulates population size This is a type of negative feedback

Intraspecific competition :

Intraspecific competition 12 Leads to behavioral adaptations to overcome or cope with competition such as Dispersal by wind, fur of animals, in gut of fruit-feeding birds and mammals or water currents Eg . Galinsoga parviflora Territoriality for general /specialized purposes


The red grouse males stake out territories that are defended against other males. The size of a territory determines red grouse density. This is called territorial behavior. Territoriality 13


Territoriality Territorial behavior has evolved in many species as a response to intraspecific competition. Male red wing blackbirds stake out a territory in defense of nests and mates. 14

Kinds of intraspecific competition:

Kinds of intraspecific competition Adapted  or programmed intraspecific competition Results from aggressive social behavior such as dominance hierarchies and territoriality. Here only certain individuals high in the peck-order, or holding territories, succeed in breeding . Also called   contest competition because it involves aggressive contests between competing individuals . Observed in white-faced capuchin monkeys ( Cebus capucinus ) 15

Kinds of intraspecific competition:

2) Unadapted or incidental  intraspecific competition R esults under high densities, no individual gets enough to survive, and the population crashes. Also called   scramble competition because everybody is involved in a mad scramble for the scarce resources. Observed in Sheep blowfly, Lucilia cuprina Kinds of intraspecific competition 16

Self thinning :

Self thinning Result of intraspecific competition. 17 Self thinning in populations of grass  Sorghastrum nutans

Interspecific competition:

Interspecific competition Competition occurs between members of the different species. Individuals of one species suffer a reduction in fecundity, survivorship, or growth as a result of resource. Starlings tend to fight off Purple Martins, kill nestlings, and break their eggs 18

Interspecific competition:

Interspecific competition The Grey Squirrel ( Sciurus carolinensis ) was introduced to Britain in about 30 sites between 1876 and 1929. It has easily adapted to parks and gardens replacing the red squirrel. The Red Squirrel ( Sciurus vulgaris ) is native to Britain but its population has declined due to competitive exclusion, disease and the disappearance mature conifer forests in lowland Britain. Grey Squirrel Range Red Squirrel Range Maps prepared by the Biological Records Centre, CEH Monks Wood, from records collated by the Mammal Society and others mainly between 1965 and 1993, also including earlier, published records and a few additions up to 1997. 19

Interspecific competition:

Barnacle species are distributed in distinct zones. Balanus in lower intertidal zone Mean tide level Interspecific competition 20

Impact of Competition:

Impact of Competition Species B 21

Possible Outcomes of Competition:

Possible Outcomes of Competition 1. One wins; other loses ….. (competitive exclusion) 2. One wins; other adapts…… (Character displacement) 3. Neither wins …….. (coexistence) 4. Both lose …….. (mutual extinction) Only 1,2, and 3 above are of ecological or evolutionary significance 22

Competitive Exclusion Principle:

Competitive Exclusion Principle No two species can occupy the same niche in the same habitat at the same time Formulated by G F Gause based on experiments with Paramecia and yeast. 23 Eg: Two species of Paramecia will thrive separately, but when put together, one species is eliminated “Complete competitors cannot coexist.”

Limitations of CEP:

Limitations of CEP Models have only two species Competitors have exactly the same resource requirements. Environmental conditions remain constant The two species are not equal competitors 24


Resource partitioning = species use different resources Or they use shared resources in different ways Ex: One species is active at night, another in the day Ex: One species eats small seeds, another eats large seeds Resource Partitioning 25


Fig. 4-5, p. 68 Louisiana heron wades into water to seize small fish Black skimmer seizes small fish at water surface Ruddy turnstone searches under shells and pebbles for small invertebrates Avocet sweeps bill through mud and surface water in search of small crustaceans, insects, and seeds Brown pelican dives for fish, which it locates from the air Dowitcher probes deeply into mud in search of snails, marine worms, and small crustaceans Herring gull is a tireless scavenger Flamingo feeds on minute organisms in mud Scaup and other diving ducks feed on mollusks, crustaceans, and aquatic vegetation Piping plover feeds on insects and tiny crustaceans on sandy beaches Knot (sandpiper) picks up worms and small crustaceans left by receding tide Oystercatcher feeds on clams, mussels, and other shellfish into which it pries its narrow beak Environmental Science: Problems, Concepts, and Solutions. (12th ed.) by G. Tyler Miller, Jr. and Scott Spoolman Resource Partitioning 26 Specialized feeding niches of various bird species in a coastal wetland.


Fig. 6-4, p. 112 Cape May Warbler Blakburnian Warbler Black-throated Green Warbler Yellow-rumped Warbler Bay-breasted Warbler Environmental Science: Problems, Concepts, and Solutions. (12th ed.) by G. Tyler Miller, Jr. and Scott Spoolman Resource Partitioning 27 R esource partitioning of five species of insect-eating warblers in the spruce forests of the U.S. state of Maine.

Resource partitioning:

Obviates competitive exclusion, Allows the coexistence of several species using the same limiting resource. Resource partitioning leads to evolutionary response to interspecific competition, or it could simply be that competitive exclusion eliminates all situations where resource partitioning does not occur. Resource partitioning 28


Coexistence Stable coexistence requires niche differentiation, such that members of each species compete more strongly among themselves than with members of the other species. (intraspecific > interspecific) “ Limiting similarity ” is the critical threshold of niche differentiation in resource utilization. Limit in the similarity of the competing species is caused by balance between i) intensity of interspecific competition ii) intensity of intraspecific competition 29 Resource utilization curves for two species

Character displacement:

Character displacement Organisms may develop morphological differences because of competition for resources. Evolution of anatomical differences that reduces competition Happens mostly where ranges of competitors overlap 30 Eg: In Darwin’s finches, species found in separate locations have the same beak size. The same species found together have different beak sizes. allows them to feed on different seeds and reduces competition


Observed in ( Chthamalus (top) populations are overgrown in the lower intertidal zone by Balanus bottom). Competitive release Niche of the competitively-inferior species expands in the absence of the competitively-superior species 31


Growth rate Location in intertidal zone low high middle Chthamalus alone fundamental niche realized niche Chthamalus with Balanus competitive release Competitive release 32 Realized niche (range of conditions) of Chthamalus smaller than its fundamental niche; no difference in these niches of Balanus Mechanism: interference by Balanus individuals (dominant competitor) Asymmetric competition

Apparent competition:

Apparent competition This occurs indirectly between two species which are both preyed upon by the same predator. Nettle aphids (prey A) and grass aphids (prey B) are prey to Coccinellidae (predator) 33

Apparent competition:

Apparent competition 34 Affects by increasing the local predator population.

Lotka-Volterra interspecific competition model:

Lotka-Volterra interspecific competition model 35


The Lotka-Volterra Model of Competition (1925-1928) 36


The equation for species 1 growing alone: The equation for species 2 growing alone: Logistic growth equation of population growth where N 1 =Population of Species 1, N 2 =Population of Species 2 K 1 =Carrying Capacity of Species 1 K 2 =Carrying Capacity of Species 2 r1 = Rate of increase of Species 1 r2 = Rate of increase of Species 2 37


The growth curves for the two species, each growing alone… Logistic growth curve of both the species 38


The equations basically indicate that a portion of the resource that could have contributed to the carrying capacity for each species growing alone is used up by the competing species. Competition is incorporated by specifying constants, called the competition coefficients , that represent the strength of the competitive interaction Suppose that it takes two individuals of species 2 to have the same effect on an individual of species 1 as one individual of species 1 on species 1; then  12 = 0.5 There are two coefficients, each representing the effect of one species on the other. We add them to the two logistic equations as follows: The Lotka-Volterra Model of Competition 39


 1,2 N 2 = Competition coefficient indicates the relative amount used by species 2 individuals compared to species 1  2,1 N 1 = Competition coefficient indicates the relative amount used by species 1 individuals compared to species 2 Logistic equation of population growth 40


Role of competition on carrying capacity of populations 41


Consider the populations of two species plotted on the X and Y axes respectively. For the species on the X axis, (Sp 1) a diagonal line can be drawn. This is an isocline. To the right of it, species 1 will decrease in number, to the left of it, species 1 will increase in number. Zero growth isoclines from Lotka-Volterra competition equations 42


Intraspecific competition alone stops population growth of sp 1 Interspecific competition alone stops growth of species 1 Some combination of the two stops population growth of species 1 43 Species 2 Zero growth isocline


Similarly, for species 2… Species 2 Zero growth isocline 44


K 2 K 2/ a 21 Merging the two isoclines 45


Notice, this particular pair of isoclines, there is one area where species 1 increases and species 2 decreases, and one area where the reverse is true K 2 K 2/ a 21 here here 46


Thus, a stable equilibrium exists where the two species can coexist K 2 K 2/ a 21 here 47


Outcomes of Lotka-Volterra model 48


Outcomes of Lotka-Volterra model 49


Plot both zero growth isoclines together on the same plot All 4 alternate outcomes of Lotka-Volterra model 50


Although somewhat abstract, and very simple, the Lotka-Volterra model makes interesting predictions-some of which are testable. In theory, both alpha and K are measurable. Summary Outcome One species is not limited by its competitor and exerts strong interspecific competition (a), (b) One species wins Both species have intense intraspecific competition (possibly due to niche differentiation) (c) Coexistence Both species have intense interspecific competition (possibly due to co-operation within a species) (d) One species excludes other, but the outcome depends on the starting densities (unstable coexistence may temporarily occur) 51


(Remember that this model is based on the logistic equation, so its assumptions still apply.) All individuals within each species are equivalent. Constant r and K No time lags in density responses α 1,2 and α 2,1 are constant, and independent of population size. Environment constant (no disturbances), homogeneous; no differences among individuals. No mechanism of competition specified Assumptions of the Lotka-Volterra model for competition 52

Criticisms of Lotka-Volterra Model:

Difficult to test explicitly, except in laboratory It assumes competition itself is density-independent. Rarely do coefficients remain constant at all population Does not model systems well when interference mechanisms involved Model does not specify any mechanism of interaction between consumers and resources (it probably best exemplifies exploitation competition) The equations really only function well for two species interaction. The equations assume environmental constancy and logistic growth in the absence of competition. The approach ignores other ecological processes/interactions and their possible effects on the competition. It uses the results, i.e. the population sizes of the species, but does not deal explicitly in the mechanism – resource use. Criticisms of Lotka-Volterra Model 53

Conclusions: :

Conclusions:  The Lotka-Volterra model of interspecific competition has been a useful starting point for biologists thinking about the outcomes of competitive interactions between species. The assumptions of the model (e.g., there can be no migration and the carrying capacities and competition coefficients for both species are constants) may not be very realistic, but are necessary simplifications. A variety of factors not included in the model can affect the outcome of competitive interactions by affecting the dynamics of one or both populations. Environmental change, disease, and chance are just a few of these factors. 54

Question from CSIR-NET paper Dec-2014:

Question from CSIR-NET paper Dec-2014 55

Answer: :

Answer: 56

Question from CSIR-NET paper Dec-2014:

Question from CSIR-NET paper Dec-2014 57 Answer: 1


Predation 58

Role of predator in the ecosystem :

Role of predator in the ecosystem Acts as ‘conduits’ for energy transfer to higher tropical region. Keeps the prey population under control, which otherwise can reach very high population density and cause imbalance in the ecosystem. Helps in maintaining species diversity in a community by reducing the intensity of competition among the competing prey species. 59

Predation :

Predation What is the nature of predation? What are the effects of predation on the predators themselves and on their prey? How do the effects vary? Why do they vary? What determines where predators feed and what they feed on? 60


Predation Describes a biological interaction where a predator (an animal that is hunting) feeds on all or part of its prey (the animal that is attacked). 61

Examples of predation:

Examples of predation Lions and Zebras 62 Lions and Zebras

Examples of predation:

Examples of predation 63 Galapagos tortoises and cactus plants

Types of predator on the level of consumption:

Types of predator on the level of consumption True predators Grazers Parasites Kill their prey soon after attacking them Kill prey gradually (or not at all), and consume part of the individual Lives in close association with a single prey individual, often inside the host Tigers, eagles Sheep and cattle, leeches, flies Bacteria and viruses 64

Types of predation on the basis of eating habits:

Types of predation on the basis of eating habits -Herbivory- consumption of plant or algal tissue 65


HERBIVORY Occurs when animals eat plants. Herbivores are those animals that exclusively or primarily eat plant tissue. Generally restricted to specific parts of the plant (leaves, flowers, fruits, roots, tubers, sap); thus, leaving the rest to regenerate. Resembles predation when seed (which contains plant embryo), seedling or whole plant is consumed. 66

Pictures of Herbivores:

Pictures of Herbivores Rabbit Turtle Caterpillar Orangutan White-tailed Deer 67

What an Herbivore eats:

What an Herbivore eats Trees/Roots/Leaves/Bark Grasses Flowers Seeds 68


VERTEBRATE HERBIVORES Large ungulates are the most conspicuous native herbivores in North America. Those that feed primarily on grasses and forbs are grazers. Those that feed on tree leaves are browsers. 69


INVERTEBRATE HERBIVORES Half of all insect species are thought to be herbivores. Groups such as butterflies, moths, weevils, leaf beetles, gall wasps, leaf-mining flies and plant bugs are almost exclusively plant eaters. Snails, slugs, mites and millipedes are largely herbivores. 70


HERBIVORY Suggested positive impacts include: Increased production and nutrient uptake. Increased quality of leaf litter and soil. Increased chances of successful seedling establishment. Improved conditions for plant growth (pruning effect). 71

Some Evolutionary Responses of Plants to Herbivory:

Some Evolutionary Responses of Plants to Herbivory 1. Mechanical forms of protection: Microscopic crystals in tissues, thorns, hooks, spines. 2. Defensive chemicals: Strychnine, morphine, nicotine, digitoxin, etc. 3. Fruits: Attractive and tasty tissues surrounding seeds that promote dispersal. 72

Types of predation:

Types of predation - Carnivory - consumption of animal tissue 73 - Carnivory - consumption of animal tissue

Pictures of Carnivores:

Pictures of Carnivores Lion Gray Wolf Hawk Coyote Bobcat Great White Shark Mountain Lion 74


What a Carnivore Eats Animals = Meat 75

Lion & Zebra:

Lion & Zebra Carnivory predation Zebra-prey Lions-predator * While individual zebras are harmed, the prey population benefits by loss of old and sick members 76

Types of predation:

Types of predation - Omnivory - consumption of both plant and animal tissues 77

Pictures of Omnivores:

Pictures of Omnivores Raccoon Primate Hedgehog Brown Bear 78

What an Omnivore eats:

What an Omnivore eats Berries Seal Meat Antelope Meat Apples/Leaves 79

Possible Outcomes of Predation:

Possible Outcomes of Predation 1. Predator population may have little effect on abundance of prey population. 2. Predator population eradicates prey population; this may contribute to extinction of predator population due to lack of food. 3. Predator and prey populations have to coexist in dynamic equilibrium. 80

How Do Predators Respond to a Change in Prey Density?:

How Do Predators Respond to a Change in Prey Density? Numerical Response – an increase in number due to an increase in reproduction. Aggregative Response – Predators tend to aggregate where the prey is at a high density. Functional Response – the number of prey eaten by an individual predator increases as the number of prey increases. Developmental Response – individual predators eat more or fewer prey as the predator grows. 81

Numerical response:

Numerical response Effective way to regulate population size. If predator populations are unable to respond numerically, to the prey when they are abundant, they will have a limited effect on the prey populations = Mismatch Predation influences where and how species live and 82

Aggregate Response:

Aggregate Respons e Predators tend to aggregate where the prey is at a high density Aggregational response increases the stability of the spatially-distributed predator-prey (or host-parasite) system. 83 Aggregative response in the Redshank The curve plots the density of redshank in relation to the average density of its arthropod prey


Impact of predators on prey population Prey: E. coli Predator: Bacteriphage T4 Prey food source: limited by glucose Two levels: 0.1 or 0.5 mg per litter Added food supply only increased predator population. 84


Monophagous – eat one prey type. Polyphagous – eat many prey types. Oligophagous – eat several prey types 85 Types according to diet widths and composition


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 86 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 Decrease at low density as well as high, increase to maximum then declines (Right panel is predation rate, # prey consumed divided by prey density) Functional response related prey consumed to prey density 87


Functional response Type 1 – Prey consumed increases with prey density. Type 2 – Prey consumed increases rapidly with prey density, then levels off. Type 3 – Prey consumed follows a logistic pattern as prey density increases. 88


Linear Type 1 (European kestrel to vole) Mortality of prey simply density dependent No limits on system Decreasing Type 2 (weasel on rodent) Predators can only eat so much –Predator satiation Time needed to kill and eat prey becomes limiting Sigmoid Type 3 (warbler on budworm larvae) Capture rate is density dependent Availability of cover Alternative prey when preferred is rare (prey switching) Prey not part of predators search image, not a desirable food source 89 Functional response

Prey- predator population:

Prey- predator population 1. Assume an exponential growth model for a prey population living in the absence of predators. 2. Assume an exponential decline model for a predator population living in the absence of prey. 3. Assume density of predators is a function of density of prey and vice versa. 90

Prey Population Living Alone:

Prey Population Living Alone Assume a constant rate of increase in absence of predators. dN/dt = r 1 N where N = number of prey t = time r 1 = reproductive capacity of prey (births exceed deaths) 91

Predator Population Living Alone:

Predator Population Living Alone Assume a constant rate of decline in absence of predators. dP/dt = - r 2 P where P = number of predators t = time - r 2 = reproductive capacity of predators (deaths exceed births) 92

Predator and Prey Populations Living Together:

Predator and Prey Populations Living Together Assume a constant rate of increase in prey population is slowed by an amount depending on the number of predators. dN/dt = (r 1 - K 1 ) N ; where K 1 = a constant related to the effect of predation on prey. Assume a constant rate of decrease in predator population is slowed by an amount depending on the number of prey. dP/dt = ( -r 2 + K 2 ) P ; where K 2 = a constant related to the effect of predation on predators. 93

A Model Predator/Prey Cycle:

A Model Predator/Prey Cycle This graph shows a limit cycle of predators and prey. 94

Description of dynamic Equilibrium between prey and predator:

Description of dynamic Equilibrium between prey and predator When predator numbers are low, prey numbers increase rapidly. As prey numbers increase, predators begin to increase. When predators numbers are high, prey numbers decrease rapidly. As prey numbers decrease, predator numbers fall. 95

Basic Equations: Prey :

Basic Equations: Prey dV/dt = rV - cPV where rV defines the maximal, geometric rate c = predator foraging efficiency: % eaten P = number of predators V= number of prey, so PV = number of encounters and cPV = number of prey killed (consumed) So, the formula describes the maximal growth rate, minus the number of prey individuals lost by predation. 96

Predator :

Predator dP/dt = a(cPV) - dP where CPV equals the number of prey consumed, and a = the rate at which food energy is converted to offspring. So, a(cPV) = number of predator offspring produced. d = mortality rate, and P = # of predators, so dP = number of carnivores dying. The equation boils down to the birth rate (determined by energy "in" and conversion rate to offspring) minus the death rate. 97


Lotka - Volterra predator-prey model 98

Predator-prey population fluctuations in Lotka-Volterra model:

Predator-prey population fluctuations in Lotka-Volterra model 99 The


The Lotka-Volterra curve assumes that prey destruction is a function not only of natural enemy numbers, but also of prey density, i.e., related to the chance of encounter. This model predicts the predator-prey oscillations sometimes seen in nature. Populations of prey and predator were predicted to flucuate in a regular manner ( Volterra termed this "the law of periodic cycle"). Lotka-Volterra model is an oversimplification of reality. In nature, many different factors affect the densities of predators and their prey. 100 Lotka - Volterra predator-prey model

Limitations of Lotka-Volterra model:

Limitations of Lotka-Volterra model The model predicts that an enrichment of the system will cause an increase in the equilibrium density of the predator but not in that of the prey and will destabilize community equilibrium. The model predicts that there cannot be a situation of both a very low and stable prey equilibrium density. 101


Didinium nasutum eats Paramecium caudatum : Gause’s Predation Experiments 102


P. caudatum (prey) and Didinium nasutum (predator) In initial experiments, Paramecium populations would increase, followed by a pulse of Didinium , and then they would crash.       Gause’s Predation Experiments 103


In initial experiments, Paramecium populations would increase, followed by a pulse of Didinium , and then they would crash. He added glass wool to the bottom, creating a REFUGE that the predator did not enter.       Gause’s Predation Experiments : 104


He induced oscillations by adding Paramecium as 'immigrants'       Gause’s Predation Experiments : 105


Hare Populations increase and eat vegetation Vegetation produces secondary defense compounds in response – less palatable and nutritious Triggers hare pop. crash – hares cannibalize – end up dying in great numbers Lynx continue to feed on hares, but run out of prey eventually Plant growth slowly recovers and rejuvenate hare population (Ecological Model, 2002) Oscillations of populations of snowshoe hare and lynx Over Time 106

Oscillations of the Two Populations Over Time:

Oscillations of the Two Populations Over Time (Ecological Model, 2002) Lynx 107


Predator-prey relationships often have ramifications for other parts of the ecosystem. The hare-lynx relationship is an example. Hares eat twigs, More hares = more damage to trees. More lynx = fewer hares and less damage to trees. 3 way interaction 108

Optimal Foraging Theory:

Optimal Foraging Theory Predicts behavior of predators in choosing prey Assume the predator makes a conscience decision when selecting prey when simultaneously faced with two or more choices. Assume the predator will maximize the net rate of energy gain while foraging. More energy is better for the predator because it will be able to meet its metabolic demands and still have energy for: Defending a territory Fighting Reproducing Moving 109

Maximizing Daily Energy Uptake:

Maximizing Daily Energy Uptake Search time – the time it takes a predator to search for a prey. Handling time – the time it takes a predator to kill and eat a single prey. Energy Value – the amount of energy available to the predator from the prey. Profitability – the amount of surplus energy a predator gets from a prey: Profitability = Handling Time Energy value h E = 110


If a predator has two prey types to choose from. Prey 1 is large and has a greater handling time than the smaller prey 2. However, assume the profitability is greater for prey 1, such that: h 1 E 1 h 2 E 2 > If a predator encounters a prey it must decide to eat it or ignore it. Two rules: If the predator encounters prey 1, it should always eat it because it is the most profitable. If it encounters prey 2, it should eat it if the gain from eating it exceeds the gain from rejecting it and searching for a more profitable prey 1. Profitability of predator 111


If S 1 is the average search time to find a prey 1 individual then: S 1 + h 1 E 1 h 2 E 2 > This model suggests that a predator will consume prey species 2 if the search time for prey 1 is large (energetically costly). Predators will maximize profitability. Profitability of predator 112

Optimal Foraging Theory:

Generalists predators tend to stabilize prey numbers Once a prey population gets too small, the predator will feed on something else If a prey population becomes very abundant, predators will feed on them Specialist predators tend to cause instability in prey numbers Because a specialists feeds on only one species, the predator-prey populations tend to oscillate (lynx-snowshoe hare). Optimal Foraging Theory 113

Size of Prey -Optimal Foraging Theory:

Size of Prey - Optimal Foraging Theory Predators tend to eat medium size prey If the prey is too small, the energy value is not great enough even though the handling time is small If the prey is too large, the handling time may be so great that it consumes too much of the prey’s energy value Medium size prey have maximum profitability 114


Prey switching Palatable versus less palatable Better return per kill Less energy needed to find and kill an abundant prey Model of prey switching 115


Switching occurs in the following situations: Different types of prey found in different microhabitats Consumers develop a search image towards a common prey Increased probability in pursuing, catching and handling a common prey Often – observed population “preferences” are due to an increase in the number of specialist individuals – not due to an overall change in diet amongst all individuals When tubificids and water flies offered in equal numbers Predator Switching 116

Evolution of Predator-Prey Systems:

Evolution of Predator-Prey Systems Coevolution – evolutionary change in two or more interacting species. For this chapter, the coevolution of predator and prey Prey that are best able to escape predators are strongly selected for. Those that get caught die Predators that are better able to catch prey are selected for If a predator misses a prey, it only loses its meal, not its life Intense natural selection pressure on each other 117


Plants evolve thorns, Animals evolve morphology and behavioral techniques to avoid thorns. Plants get taller, change canopy structure, animals get taller. Coevolution 118

Predator and Prey techniques:

Predator and Prey techniques 119


1) Invisibility Cloak (cryptic coloration/ camouflage) Tactics of the Predator 120


Tactics of the Predator 2) Ambush- Hide and Wait 121


3) Chemical warfare: Venoms Tactics of the Predator 122


4) “Right this Way Please”: trap-doors, nets, and other deadly devices. Tactics of the Predator 123


5) Bigger, Badder, Faster 200 mph 17,000 lbs, and perhaps as smart as you 700 lbs & built to kill Tactics of the Predator 124


Combinations- Invisibility Cloak; Patience; Bigger, Badder, Faster Tactics of the Predator 125


Responses of the Prey 1) Invisibility Cloak (cryptic colouration / camouflage) 126


Responses of the Prey 2) FLEE or fly away!!!! 127


Responses of the Prey 3) Chemical defense- “Eat me and die”- Poisons/ toxins a) Prey can synthesize toxin using their own metabolic processes, In animals Amphibians- produce skin toxins by glands. Fishes – release alarm pheromones 128 Fire salamander makes a nerve poison, which it can squirt from glands on its back. The poison dart frog has poison glands scattered all over its body.

Chemical Defense in plants:

Chemical Defense in plants Calotropis produces toxic glycoside Cyanide in white clover Nicotine in tobacco Mustard oil in cabbage Tomato produces protease inhibitors 129

Chemical defense:

Chemical defense b) Animals also accumulate toxin from the food they eat. Milkweed-prey (defense) Latex: A milky white sap that becomes sticky and coagulates when exposed to air. Cardiac glycoside : To various degrees, it is toxic to herbivores with hearts (birds and mammals). Monarchs and several other arthropods that eat milkweed have a tolerance for cardiac glycosides, although evidently not at the high levels found in some milkweed species. Monarch Butterfly-predator Monarch larve cut the petiole of the leaf before beginning to eat it. This "leaf-notching" behavior cuts off the supply of latex. Birds that eat the Monarchs vomit and learn to avoid them in the future.  130

Rough-Skinned Newt & Common Garter Snake:

Rough-Skinned Newt & Common Garter Snake Carnivory predation Newt-prey Has genes to produce potent toxins which discourage predation Snake-predator Has genes for resistance to newt toxin * Results in an “evolutionary arms race”… coevolution ! 131


Responses of the Prey 4) Aposematic coloration : Is a strategy used by some animals to alert potential predators of their presence with bold colors with patterns to promote avoidance. Predators will avoid any animal that has the colors and patterns they associate with pain , illness, or unpleasant experiences Most common warning colors are bright shades of red , yellow, orange, black, and white 132

Examples of Aposematism:

Examples of Aposematism 133


Responses of the Prey 5) “Shields up”: (armor):Protection – shells, bark, spines, thorns 134


Responses of the Prey 6) “Who wants fetid flesh for dinner? Surely not a proud hunter like yourself” (play dead): 135


Responses of the Prey 7) Mimicry: where harmless species resemble a poisonous species. Types: Aggressive mimicry – looks attractive Batesian mimicry- looks like a toxic model- but is non-toxic Mullerian mimicry- looks like a toxic model- AND is toxic 136

Aggressive Mimicry:

Aggressive Mimicry 137 The bright leaves of Dionaea muscipula attract insects in the same way as flowers. The Alligator Snapping Turtle uses its tongue to lure fish. A form of mimicry in which a predator (the mimic) closely resembles another organism (the model) that is attractive to a third organism (the dupe) on which the mimic preys.

Batesian Mimicry:

Batesian Mimicry 138 The Syrphid fly mimics the colors and markings of honey bees. The Monarch would be the model and the Viceroy the mimic. A form of protective mimicry in which an unprotected species (the mimic) closely resembles an unpalatable or harmful species (the model), and therefore is similarly avoided by predators

Müllerian Mimicry:

Müllerian Mimicry 139 A form of protective mimicry in which two or more poisonous or unpalatable species closely resemble each other and are therefore avoided equally by all their natural predators. Poison dart frogs of South America and Madagascar. Heliconius erato and H. melpomene


Responses of the Prey 8) Strength in Numbers: 140


9) Alertness – highly developed senses Fly – compound eye Rabbits- Ears 141 Responses of the Prey


10. Behavioral strategies – Puffing up (blowfish) “Bluff,” where it make a scary face or noise. 142 Responses of the Prey



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