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Species Interactions II

by: Jesse McDonald

Species Interactions II Biology 286

Marketplace > Purdue University > Biology > Biology 286 > Species Interactions II
Jesse McDonald

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About this Document

This corresponds with lecture 19.
Introduction to Ecology and Evolution
Dr. Josh Springer
Class Notes
Biology, Ecology, species, interactions
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This 4 page Class Notes was uploaded by Jesse McDonald on Tuesday March 29, 2016. The Class Notes belongs to Biology 286 at Purdue University taught by Dr. Josh Springer in Spring 2016. Since its upload, it has received 10 views. For similar materials see Introduction to Ecology and Evolution in Biology at Purdue University.


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Date Created: 03/29/16
iClicker Question:  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.  A. True  B. False    Species Interactions    Predation takes a variety of forms:  ● Predation is a direct and often complex interaction between the eater and the eaten  ● A true predato kills its prey immediately upon capture, more or less  ○ Predators consume ​multipl​prey organisms and function as agents of mortality  ○ Regulate populations     iClicker Question:  The full range of environmental conditions that an organism can live/exist in its  considered: (refer back to lecture 18 material)  A. Realized niche  B. Fundamental niche  C. Optimum niche  D. Survivorship curve  E. Niche coefficient    ● 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 a true predator.   ● 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:  ○ Intimate association with a single host  ○ The eggs hatch and the larvae feed on the host, eventually killing it.    Predators Respond Numerically to Change 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 7.5­fold 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 of foraging, predators must allocate time to:  ○ Avoiding their own predators  ○ Defense  ○ Searching for mates  ○ Caring for young  ● Meeting all of these demands requires tradeoffs  ● 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    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 take in toxic plant compounds to use in defense towards predators.  ■ Monarch butterflies feed on milkweed as caterpillars.  ○ Venomous animals produced their own toxins (poison dart frogs, snakes).  ● Cryptic coloratio ­ prey organisms possess colors and patterns that allow them to  blend into the background in their environment:  ○ This is common in fish, birds, and low­ground organisms.   ● 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 their body (such as the tail of a lizard  because lizards can regrow their tails).   ● 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, ie white tailed deer.  ○ This color flash may distract and disorient the predator.  ○ May be a signal to promote group cohesion and raise alarm when a predator is  near.  ● 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.   ● 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.  ○ Ex: Periodic cicadas have a mass emergence as adults in North America after 13  to 17 years.  ■ Only a small proportion of them are going to be eaten in 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, and spines.  ● 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 high­quality plant material rich in nitrogen  ○ High­quality foods are young, soft, and green; or are storage structures such as  roots, tubers, or seeds.  ○ Low­quality 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 organism:  ● Parasites increase their fitness by using the host in a close, prolonged association for  food, habitat, and dispersal.  ● They do not want to kill their host!  ● Host fitness is often decreases by the parasite through stunted growth, emaciation  (abnormal thinness due to lack of nutrients), behavior modification, and sterility.  ● The host may also die from a secondary infection.   ● We will consider a parasite an organism that fits the narrow description.     


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