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Predation Parasitism Mutualism

by: Sierra

Predation Parasitism Mutualism Biol 28600

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About this Document

Lecture 18
Introduction to Ecology and Evolution
Joshua Springer
Class Notes
Ecology, evolution, Biology
25 ?




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This 45 page Class Notes was uploaded by Sierra on Friday April 8, 2016. The Class Notes belongs to Biol 28600 at Purdue University taught by Joshua Springer in Spring 2016. Since its upload, it has received 11 views. For similar materials see Introduction to Ecology and Evolution in Biology at Purdue University.


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Date Created: 04/08/16
Announcements  Curve for Exam II is 14. You will see a separate column on BB for 14/0 soon.  Curve for Exam I is 2. I will add a column for those points as well  Key and Questions will be posted later to BB  Exam III is April 14 and is ONLINE! More information as the date approaches iClicker  In general, a trait does not need to be heritable for a change in phenotypic value to be evident from one generation to the next This statement is: A) True B) False Predation Parasitism © 2015 Pearson Education, Inc. Mutualism Parasitoidism (Parasitoids) Up to 65 C © 2015 Pearson Education, Inc. © 2015 Pearson Education, Inc. Predation Takes a Variety of Forms  Carnivores – consume animal tissue  Herbivores – consume plant or algal tissue  Omnivores – consume plant and animal tissue  Predation is a direct and often complex interaction between the eater and the eaten  A true predator (predator) kills its prey immediately upon capture, more or less  Predators consume multiple prey organisms and function as agents of mortality  Regulate populations Switch prey when prudent or necessary © 2015 Pearson Education, Inc. © 2015 Pearson Education, Inc. © 2015 Pearson Education, Inc. iClicker  The full range of environmental conditions that an organism can live/exist in is considered:  A) Realized niche  B) Fundamental niche  C) Optimum niche  D) Survivorship curve  E) Niche coefficient Predation Takes a Variety of Forms  Herbivores include grazers and browsers  Generally they consume only part of an individual plant  This may harm the plant but usually does not kill it  Seed predators and planktivores are exceptions because they kill their “prey,” functioning as true predators © 2015 Pearson Education, Inc. Predation Takes a Variety of Forms  Parasites feed on the live host organism  often an intimate relationship, with the parasite living on or in the host at least part of its life cycle  Activity is harmful but generally not lethal, at least in the short term  Parasitoids attack the prey indirectly by laying eggs on the host’s body  an intimate association with a single host  The eggs hatch and the larvae feed on the host, eventually killing it Figure 14.3b 1 2 3 4 Prey Predator Population size Time (b) © 2015 Pearson Education, Inc. Predators Respond Numerically to Changing Prey Density  Sometimes there is a lag between the prey and predator populations in the numerical response of the predator  Field study of Canadian lynx (predator) and snowshoe hare (prey) in Yukon Territory, Canada between 1986 and 1995  Lynx population increased 7.5-fold in response to dramatic increase in hares  This increase was about a year behind the time of peak abundance of hares Foraging Involves Decisions about the Allocation of Time and Energy  In addition to foraging, predators must allocate time to  avoiding their own predators  defense  searching for mates  caring for young  Meeting all of these demands requires trade-offs Foraging Involves Decisions about the Allocation of Time and Energy  Optimal foraging theory – natural selection favors “efficient” foragers, individuals that maximize their nutrient intake per unit of effort  What types of decisions does an organism make relative to optimal foraging? To forage efficiently, an organism must determine what food to eat where to search for food how to search for food how long to search for food Use the cost and benefit approach cost – time and energy expended for foraging benefit – increased fitness as measured in terms of energy or nutrient gain, which is assumed to correlate with fitness Small prey – easy to handle but too little energy gained Large prey – hard to handle relative to energy gained © 2015 Pearson Education, Inc. Coevolution Can Occur between Predator and Prey  As characteristics evolve in prey that reduce their chance of being caught and eaten, this exerts selective pressure on predators  Failure to capture prey reduces predator fitness through reduced reproduction and increased mortality  More effective means of capturing prey evolve in the predator  This coevolutionary “race” is continual – predator and prey are evolving simultaneously, which maintains their relationship Animal Prey Have Evolved Defenses against Predators  Chemical defenses are widespread  Alarm pheromones signal other individuals in the same or related species to flee  Arthropods sequester toxic plant compounds  Monarch butterflies feed on milkweed as caterpillars  Venomous animals produce their own toxins  poison dart frogs, snakes Animal Prey Have Evolved Defenses against Predators  Cryptic coloration – prey organisms possess colors and patterns that allow them to blend into the background in their environment  This is common in fish, reptiles, and ground-nesting birds Animal Prey Have Evolved Defenses against Predators  Object resemblance is a defense in which the organism looks like an object or part of another organism in the environment  Many insects use this  Walking sticks resemble twigs  Some animals have eyespots, which may intimidate potential predators or trick them into attacking a less vulnerable part of the body Animal Prey Have Evolved Defenses against Predators  Flashing coloration is often associated with cryptic coloration  An animal displays a visible patch of color when disturbed that vanishes when it is at rest  seen in butterflies, grasshoppers, birds, ungulates  This color flash may distract and disorient the predator  May be a signal to promote group cohesion and raise alarm when a predator is present  White-tailed deer show a white patch under the tail Figure 14.16 Coral Snake King Snake (a) (b) © 2015 Pearson Education, Inc. Animal Prey Have Evolved Defenses against Predators  Living in a group is a simple defense strategy  Most predators are less likely to attack a group of individuals  A tight, unified group makes it more difficult for a predator to take a single individual  Group flight can confuse a predator Animal Prey Have Evolved Defenses against Predators  A change in reproductive timing can result in most offspring being produced in a short time  In predator satiation, prey are so abundant that the predator can only take a fraction of them, so most escape predation  Periodic cicadas have a mass emergence as adults in North America after 13 or 17 years  Local density can be millions per hectare  This leads to predator satiation; only a small proportion is eaten at high densities Plants Have Evolved Characteristics that Deter Herbivores  Plants cannot run away from their predators so have evolved an array of adaptations that deter herbivores from feeding on them  Some defenses are structural; others are chemical  Benefit of the defense must outweigh cost of production  Structural defenses include  hairy leaves  thorns  spines Figure 14.23 © 2015 Pearson Education, Inc. Plants Have Evolved Characteristics that Deter Herbivores  For herbivores, quality of food rather than quantity is often the main constraint  Plant tissues contain cellulose  Complex animal digestion is required to convert plant tissues into animal biomass  Herbivores need high-quality plant material rich in nitrogen  High-quality foods are young, soft, and green or are storage structures such as roots, tubers, seeds  Low-quality foods are tough, woody, and fibrous Parasitism and Mutualism  Symbiosis – the intimate and protracted association between two or more organisms of different species  The fate of individuals of one species depends on their association with individuals of another  The result of the association may be positive, negative, or benign  This encompasses a wide variety of interactions Parasites Draw Resources from Host Organisms  Parasites increase their fitness by using the host in a close, prolonged association for  food  habitat  dispersal  They usually do not kill the host Parasites Draw Resources from Host Organisms  Host fitness is often decreased by the parasite through  stunted growth  emaciation  behavior modification  sterility  The host may die from a secondary infection Parasites Draw Resources from Host Organisms  Parasites generally  are much smaller than the host  are highly specialized  reproduce more quickly and in larger numbers than the host Parasites Draw Resources from Host Organisms  We will consider a parasite an organism that fits the narrow description  Parasites are found in many groups  viruses, bacteria, protists, fungi, plants, invertebrates  A heavy load of parasites is an infection, and the outcome of an infection is disease  Parasites can be categorized by size Hosts Provide Diverse Habitats for Parasites  Ectoparasites live on the outside of the host  Ectoparasites of vertebrates live in the skin, feathers, scales, hair  Ectoparasites of insects live on the legs, upper and lower body surfaces, the mouthparts  Endoparasites live within the host  Some may burrow under the skin  Some live in the blood  Some live in organs, or within lining tissues, such as the nasal tract Parasites May Regulate Host Populations  Several tree species in North America have been adversely affected by introduced parasites  Chestnut blight (fungal parasite) was introduced from Europe into North America  has virtually exterminated the American Chestnut tree, a dominant part of the eastern forests  Dutch elm disease (fungal parasite) has decimated elms in North America  Anthracnose (fungal parasite) has infected dogwoods, an important understory tree Parasitism Can Evolve into a Mutually Beneficial Relationship  Parasitism is a symbiotic relationship  Parasite benefits at the expense of the host  Hosts evolve defenses to reduce the parasite’s negative effect  What happens if the host adaptations have completely countered the negative impacts?  Can a host-parasite relationship become beneficial to both species through coevolution? Parasitism Can Evolve into a Mutually Beneficial Relationship  If a host has completely countered the negative effects of the parasite, the relationship could become commensalism: one species benefits while the other is largely unaffected  If the relationship becomes beneficial to both host and parasite, it would be mutualism  There are examples of parasitic relationships in which the host seems to receive a benefit from the presence of the parasite Mutualisms Involve Diverse Species Interactions  Mutualism is a positive interaction between two species that can be characterized by a number of benefits  The variety of benefits received  provision of essential resources (food, shelter)  protection from predators, herbivores, parasites  reduction of competition with a third species  enhanced reproduction Mutualisms Involve Diverse Species Interactions  Obligate mutualists cannot survive or reproduce without the interaction  Facultative mutualists can survive and reproduce without the interaction  The degree of specificity of a mutualism can vary  Specialist mutualists have a one-to-one species specific association  Generalist mutualists associate with a diversity of partners of different species Mutualisms Are Often Necessary for Pollination  There are two main mechanisms of pollen dispersal  Wind carries pollen from one plant to another  grasses, many trees (especially conifers)  effective for plants growing in large, homogenous stands  less reliable when individuals of a species are widely spaced and scattered Mutualisms Are Often Necessary for Pollination  Animal carries pollen from one plant to another  Plant benefits through achieving fertilization  Plant attracts animal through color, fragrance, and food (pollen, nectar, and oils)  mainly insects, birds, and bats  presents a cost for the plant because it must expend energy that could be used for growth  Nectars and oils are produced only to attract pollinators Figure 15.15


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