Ecology Chapter 14 Exploitative Interactions PDF

Chapter 14 Exploitative Interactions: Predation, Herbivory, Parasitism, and Disease © 2019 McGraw-Hill Education. All rights reserved. Authorized only for instructor use in the classroom. No reproduction or further distribution permitted without the prior written consent of McGraw-Hill Education....

Chapter 14 Exploitative Interactions: Predation, Herbivory, Parasitism, and Disease © 2019 McGraw-Hill Education. All rights reserved. Authorized only for instructor use in the classroom. No reproduction or further distribution permitted without the prior written consent of McGraw-Hill Education.  Outline Concept 14.1 Predators, parasites, and pathogens influence the distribution, abundance, and structure of prey and host populations. Concept 14.2 Predator-prey, host-parasite, and host-pathogen relationships are dynamic. Concept 14.3 To persist in the face of exploitation, hosts and prey need refuges. Concept 14.5 Exploitative interactions weave populations into a web of relationships that defy easy generalization. © 2019 McGraw-Hill Education.  Introduction Exploitation – interaction that enhances fitness of one individual while reducing fitness of the exploited individual. Predators kill and consume other organisms. Parasites live on host tissue and reduce host fitness, but do not generally kill the host. Parasitoid is an insect larva that consumes the host. Pathogens induce disease. © 2019 McGraw-Hill Education.  14.1 Exploitation and Abundance Predators, parasites, and pathogens influence the distribution, abundance, and structure of prey populations. Exploitative interactions have potential to influence prey and host populations. © 2019 McGraw-Hill Education.  A Herbivorous Stream Insect and Its Algal Food Lamberti and Resh (1983) studied influence of caddisfly (Helicopsyche borealis) larvae on algal and bacterial populations on which it feeds. At times the larvae can make up 25% of the biomass of benthic animals. Experiment showed that larvae reduce the abundance of their food supply. © 2019 McGraw-Hill Education. A Herbivorous Stream Insect and Its Algal Food © 2019 McGraw-Hill Education.  Bats, Birds, and Herbivory in a Tropical Forest Kalka et al. (2008) examined how birds and bats affected tropical forest arthropods. Treatments included controls, daytime bird exclusion, and nighttime bat exclusion. Compared to controls: Bird exclusion increased arthropods by 65%. Bat exclusion increased arthropods by 150%. © 2019 McGraw-Hill Education.  Influence of Bat and Bird Exclusion Copyright © McGraw-Hill Education. Permission required for reproduction or display. Access the long description slide. © 2019 McGraw-Hill Education.  A Pathogenic Parasite, a Predator, and Its Prey Lindstrom et al. (1994) studied spread of mange mites (Sarcoptes scabiei) on foxes in Sweden and indirect effects on foxes’ prey. Mange mites cause hair loss, deterioration and death in foxes. Fox populations declined by 70%. Number of mountain hares (Lepus timidus), a prey species, increased 2 to 4 times after fox population declined. © 2019 McGraw-Hill Education.  Red Foxes and Mountain Hares Copyright © McGraw-Hill Education. Permission required for reproduction or display. Access the long description slide. © 2019 McGraw-Hill Education.  Click to edit Master title style © 2019 McGraw-Hill Education.  14.2 Dynamics Cycles of Abundance in Snowshoe Hares and Their Predators. Snowshoe hares (Lepus americanus) and lynx (Lynx canadensis) have well documented population cycles. Elton proposed abundance cycles driven by variation in solar radiation. Keith suggested “overpopulation theories”: Decimation by disease and parasitism. Physiological stress at high density. Starvation due to reduced food. Alternatively, hare cycle is driven by predators. © 2019 McGraw-Hill Education.  Lynx and Hare Population Fluctuations Copyright © McGraw-Hill Education. Permission required for reproduction or display. Access the long description slide. © 2019 McGraw-Hill Education.  The Role of Food Supply Hares live in conifer dominated boreal forest. Dense growth of understory shrubs. Hare density can reach 1,100 to 2,300/km. 2 In winter, browse on buds and stems of shrubs and saplings. One population reduced food biomass from 530 to 160 kg/ha over 4 months. Shoots produced after heavy browsing can increase levels of plant chemical defenses. Reduces usable food supplies during population declines. © 2019 McGraw-Hill Education.  The Role of Predators Lynx are one predator of snowshoe hares. Other predators also play a large role. Predation can account for 60 to 90% of hare mortality during peak densities. Predators exhibit functional and numerical response to increased hare density. Both predation and food contribute to hare population cycles – they are complementary. Hares increase, reducing quantity and quality of food while predation increases. © 2019 McGraw-Hill Education.  Experimental Test of Food and Predation Impacts Krebs et al. (1995) conducted field experiment to test impacts of food and predators on snowshoe hares. Found increased hare numbers with. Increased food availability, reduced predation, and a combination of the two. Conclude that hare population cycle is result of interaction among 3 trophic levels. Hares, their plant food supply, and their predators. © 2019 McGraw-Hill Education.  Densities of Snowshoe Hares Copyright © McGraw-Hill Education. Permission required for reproduction or display. Access the long description slide. © 2019 McGraw-Hill Education.  Population Cycles in Mathematical and Laboratory Models Lotka-Volterra assumes host (prey) population grows exponentially, and population size is limited by parasites, pathogens, and predators: dNh = rh Nh − pNh Np dt rhNh = exponential growth by host population, which is opposed by: P = rate of parasitism/predation. Nh = Number of hosts. Np = Number of parasites/predators. © 2019 McGraw-Hill Education.  Growth of Predator Population Lotka-Volterra assumes parasite/predator growth rate is determined by rate of conversion of food into offspring minus mortality rate of parasite/predator population: dNp = cpNh Np − d p Np dt cpNhNp = conversion rate of hosts into parasite/predator offspring. Where c is a conversion factor and p is the rate of parasitism/predation. dpNp = parasite/predator deaths. © 2019 McGraw-Hill Education.  Model Behavior Host exponential growth often opposed by exploitation. Host reproduction immediately translated into destruction by predator. Increased predation = more predators. More predators = higher exploitation rate. Larger predator population eventually reduces host population, in turn reducing predator population. Produces oscillations in both populations. © 2019 McGraw-Hill Education.  Lotka-Volterra Predator-Prey Model Copyright © McGraw-Hill Education. Permission required for reproduction or display. Access the long description slide. © 2019 McGraw-Hill Education.  Unrealistic Assumptions Despite unrealistic assumptions: Prediction of eternal oscillations along narrow path. Neither population is subject to carrying capacities. Changes in one population result in immediate response by other. L-V models made valuable contributions by demonstrating that predator-prey interactions can produce population cycles. © 2019 McGraw-Hill Education.  Laboratory Models Utida found reciprocal interactions in adzuki bean weevils Callosobruchus chinensis and a parasitoid wasp, Heterospilus prosopidis, over 112 generations. Gause found similar patterns in P. aurelia preying on yeast in a shorter experiment. Most laboratory experiments have failed to produce L-V oscillations. Most lead to extinction of one population within a relatively short period. © 2019 McGraw-Hill Education.  14.3 Refuges To persist in the face of exploitation, hosts and prey need refuges. Refuge and Host Persistence in Laboratory and Mathematical Models. Gause attempted to produce population cycles with P. caudatum and Didinium nasutum. Didinium quickly consumed all Paramecium; both went extinct. With sediment (Paramecium refuge), Didinium went extinct and a few Paramecium survived. © 2019 McGraw-Hill Education.  Refuges and Persistence of Predator-Prey Oscillations Copyright © McGraw-Hill Education. Permission required for reproduction or display. Access the long description slide. © 2019 McGraw-Hill Education.  Refuges and Mites Huffaker studied a prey species, the six-spotted mite (Eotetranychus sexmaculatus) and a predator mite Typhlodromus occidentalis. Habitats were oranges and rubber balls with partial barriers to mite dispersal. Typhlodromus crawls while Eotetranychus crawls or balloons. Both species maintained population oscillations spanning 6 months (3 cycles). © 2019 McGraw-Hill Education.  Population Cycles of Mites Copyright © McGraw-Hill Education. Permission required for reproduction or display. Access the long description slide. © 2019 McGraw-Hill Education.  Exploited Organisms and Their Wide Variety of “Refuges” Refuges can take a variety of forms. Flight for a bird, large size, etc. Space. Spatial refuges include burrows, trees, etc. Invasive Opuntia stricta cactus has small isolated populations as spatial refuges. Herbivorous insects don’t find them. St. John’s wort also persists in small populations. Protected from beetle predators. © 2019 McGraw-Hill Education.  Protection in Numbers Living in a large group provides a refuge. Predator’s response to increased prey density: Prey consumed Predators Prey consumed × = Predator Area Area Many species use predator satiation defense. Prey can reduce individual probability of being eaten by living in dense populations. Beyond a threshold, increases in prey density do not lead to increases in predator density or feeding rates. © 2019 McGraw-Hill Education.  Prey Density and Number of Prey Consumed Copyright © McGraw-Hill Education. Permission required for reproduction or display. Access the long description slide. © 2019 McGraw-Hill Education.  The Ecology of Fear and Refuges Predators can influence prey populations by altering their behavior - “the ecology of fear.” Reintroduction of gray wolves (Canis lupus) to Yellowstone National Park has resulted in elk (Cervus elaphus) avoiding riparian areas. Riparian trees, especially willow, may be increasing in abundance as a result of the reduced foraging by elk. © 2019 McGraw-Hill Education.  14.5 Complex Interactions Exploitative interactions weave populations into a web of relationships that defy easy generalization. Conservatively there are 10 million species. Number of exploitative interactions is far greater. Lake Okeechobee, Florida, contains approximately 500 known species. Linked by approximately 25,000 exploitative interactions (50 times the number of species). © 2019 McGraw-Hill Education.  Parasites and Pathogens That Manipulate Host Behavior Parasites That Alter the Behavior of Their Hosts. Spiny-headed worms (Acanthocephalans) change behavior of amphipods, making it more likely that infected amphipods will be eaten by a suitable vertebrate host. Infected amphipods exhibit positive phototaxis, which puts them closer to surface predators. Uninfected amphipods exhibit negative phototaxis, away from the suitable vertebrate hosts. © 2019 McGraw-Hill Education.  Impact of Plagiorhynchus on Host Behavior Copyright © McGraw-Hill Education. Permission required for reproduction or display. Access the long description slide. © 2019 McGraw-Hill Education.  A Plant Pathogen That Mimics Flowers Rust fungus Puccinia monoica manipulates growth of host mustard plants (Arabis spp.). Puccinia infects Arabis rosettes and invades actively dividing meristemic tissue. Rosettes rapidly elongate and become topped by a cluster of bright yellow leaves. These pseudoflowers are fungal structures, including reproductive structures. They secrete sugary fluids, attracting pollinators which assist the fungus in outcrossing. © 2019 McGraw-Hill Education.  Effects of the Fungus Puccinia on Arabis Copyright © McGraw-Hill Education. Permission required for reproduction or display. Access the long description slide. © 2019 McGraw-Hill Education.  Entangling Exploitation with Competition Park found the presence/absence of a protozoan parasite (Adelina tribolii) influences competition in flour beetles (Tribolium). Effects of parasite are entangled with predation among beetles and cannibalism. T. castaneum is the most cannibalistic. Adelina reduces density of T. castaneum but has little effect on T. confusum. Without Adelina, T. castaneum is usually the strongest competitor; with Adelina, T. confusum becomes strongest competitor. © 2019 McGraw-Hill Education.  Influence of Adelina on Tribolium Competition Copyright © McGraw-Hill Education. Permission required for reproduction or display. Access the long description slide. © 2019 McGraw-Hill Education.  Review Introduction. Exploitation and Abundance. Dynamics. Refuges. Complex Interactions. © 2019 McGraw-Hill Education.