Chapter 13: Species Interactions and Competition PDF

Chapter 13 Species Interactions and Competition © 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 13 Species Interactions and Competition © 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 13.1 Laboratory and field studies reveal intraspecific competition. Concept 13.2 The competitive exclusion principle proposes that two species with identical niches cannot coexist indefinitely, which leads to the prediction that coexisting species will have different niches. Concept 13.3 Mathematical and laboratory models provide a theoretical foundation for studying interspecific competition in nature. Concept 13.4 Competition can have significant ecological and evolutionary influences on the niches of species. © 2019 McGraw-Hill Education.  Introduction Species interact in different ways, with different ecological outcomes. Possible impacts on 2 interacting organisms. Positive, negative, neutral. Negative impact occurs when energy is expended or injury occurs. Symbioses occur when most/all of life cycle of one organism occurs on/in another. © 2019 McGraw-Hill Education.  Modes of Competition Interference competition - direct interactions between individuals. Aggressive territory defense, production of chemical toxins, reducing access to resources, etc. Can occur in cases of resource limitation. Intraspecific competition - competition with members of own species. Interspecific competition - competition between individuals of two species. Reduces fitness of both. © 2019 McGraw-Hill Education.  Intraspecific Competition Among Plants Plant biomass found to be higher in low density populations. Competition for resources (nitrogen) is more intense at higher densities. Usually leads to mortality among competing plants (intraspecific competition) - self-thinning. © 2019 McGraw-Hill Education. © 2019 McGraw-Hill Education.  Intraspecific Competition Among Planthoppers Denno and Roderick attributed prevalence of competition among Homoptera to. Habit of aggregating, rapid population growth, and mobile nature of food supply. Demonstrated intraspecific competition within populations of planthopper Prokelesisia marginata. Probably result of limited resources. © 2019 McGraw-Hill Education. © 2019 McGraw-Hill Education.  13.2 Competitive Exclusion and Niches Gause’s competitive exclusion principle – two species with identical niches cannot coexist indefinitely. One will be a better competitor, have higher fitness, eventually exclude other. Led to prediction that species living together generally have different niches. Niche concept helps study of ecology of interactions. Most niches determined by a few factors. © 2019 McGraw-Hill Education.  The Feeding Niches of Darwin’s Finches Grant represented various feeding niches of finches by beak size. Size of seeds eaten can be estimated by measuring beak depths. Individuals with deepest beaks fed on hardest seeds. Drought shows importance of beak size. 1977 drought reduced seeds available. Finches ate small, soft seeds first, leaving only hard seeds. Greatest mortality in small-beaked birds. © 2019 McGraw-Hill Education. © 2019 McGraw-Hill Education.  Fig. 13.10 © 2019 McGraw-Hill Education.  Selection for Larger Size Copyright © McGraw-Hill Education. Permission required for reproduction or display. Access the long description slide. © 2019 McGraw-Hill Education.  13.3 Mathematical and Laboratory Models Mathematical and laboratory models generally simpler than nature. Metz summarized models for Tribolium. Abstractions and simplifications, not facsimiles of nature. Man-made construct; partly empirical and partly deductive. Used to provide insights into natural phenomena. © 2019 McGraw-Hill Education.  Modeling Interspecific Competition Effect of interspecific competition on population growth of each species: dN1 / dt = r1N1 ((K1 − N1 − α12 N2 ) / K1 ) dN2 / dt = r2 N2 ((K2 − N2 − α21N1 ) / K2 ) α12: Effect of individual of species 2 on rate of pop. growth of species 1 α21: Effect of individual of species 1 on rate of pop. growth of species 2 © 2019 McGraw-Hill Education.  Lotka-Volterra Model In general, Lotka-Volterra model predicts coexistence of two species when. Interspecific competition is weaker than intraspecific competition for both species. Otherwise, one species will eventually exclude the other. © 2019 McGraw-Hill Education.  Isoclines of Zero Population Growth Predict population growth for the two species will stop when: N1 = K1 − α12N2 and N2 = K2 − α21N1. These are isoclines of zero population growth. Above isocline population is decreasing. Below isocline population is increasing. Coexistence of two species is only possible when isoclines cross. © 2019 McGraw-Hill Education.  Lotka-Volterra Isoclines Copyright © McGraw-Hill Education. Permission required for reproduction or display. Access the long description slide. © 2019 McGraw-Hill Education.  Experiments with Paramecia Gause demonstrated resource limitation with P. caudatum and P. aurelia in presence of two different concentrations of Bacillus pyocyaneus. When grown alone, carrying capacity determined by intraspecific competition. When grown together, P. caudatum quickly declined. Reduced resource supplies increased competition. © 2019 McGraw-Hill Education.  Paramecium Population Growth Copyright © McGraw-Hill Education. Permission required for reproduction or display. Access the long description slide. © 2019 McGraw-Hill Education.  Experiments with Flour Beetles Tribolium beetles infest stored grain products. Park studied interspecific competition between T. confusum and T. castaneum under varied environmental conditions. Growing the two species together suggested interspecific competition restricts the realized niches of both species to fewer environmental conditions. © 2019 McGraw-Hill Education. © 2019 McGraw-Hill Education.  13.4 Competition and Niches Competition can restrict species to their realized niches. But if competitive interactions are strong and pervasive enough, they may produce an evolutionary response in the competitor population. Resulting in changes to fundamental niche. © 2019 McGraw-Hill Education.  Niches and Competition Among Plants Tansley suggested interspecific competition restricts realized niche of two species of bedstraw (Galium spp.). G. saxatile grows on acidic soils. G. sylvestre grows on limestone soils. Experiments each will grow on both soil types without competition. When grown together on limestone soils, G. sylvestre quickly dominates; on acidic soils G. saxatile slowly dominates. © 2019 McGraw-Hill Education.  Fig. 13.18 © 2019 McGraw-Hill Education.  Niche Overlap and Competition Between Barnacles Connell observed interspecific competition in barnacles. Physical factors limit Balanus to lower and middle intertidal zone, but do not explain lower limit of Chthamalus. Balanus plays a role in determining lower limit of Chthamalus within intertidal zone. Balanus excludes Chthamalus from middle intertidal by intraspecific competition. © 2019 McGraw-Hill Education. © 2019 McGraw-Hill Education.  Distribution of Chthamalus Copyright © McGraw-Hill Education. Permission required for reproduction or display. Access the long description slide. © 2019 McGraw-Hill Education.  Competition and Niches of Small Rodents Brown studied competition among rodents in Chihuahuan Desert. If granivorous rodents compete for food, then populations of small rodent would increase with removal of larger rodents. Insectivorous rodents would show little or no response. Results supported hypothesis. © 2019 McGraw-Hill Education. © 2019 McGraw-Hill Education.  Responses of Rodents Copyright © McGraw-Hill Education. Permission required for reproduction or display. Access the long description slide. © 2019 McGraw-Hill Education.  Character Displacement Interspecific competition reduces fitness of competitors. Individuals that compete less should have higher fitness. Interspecific competition predicted to lead to character displacement. Two species differing more in areas where they co-occur than in areas where their distributions do not overlap. © 2019 McGraw-Hill Education.  Character Displacement in Darwin’s Finches Medium (G. fortis) and small (G. fuliginosa) ground finch exhibit character displacement. They are allopatric on Daphne Major and Los Hermanos and have similar beak sizes. They are sympatric on Santa Cruz and have dissimilar beak sizes. Allopatric G. fortis beaks are smaller than sympatric G. fortis beaks; allopatric G. fuliginosa beaks are larger than sympatric. On Santa Cruz, the species have different feeding niches. © 2019 McGraw-Hill Education.  Beak Size in Darwin’s Finches Copyright © McGraw-Hill Education. Permission required for reproduction or display. Access the long description slide. © 2019 McGraw-Hill Education.  Character Displacement Criteria (Part I) Taper and Case identify criteria for character displacement. Morphological differences between sympatric species are statistically greater than differences between allopatric populations. Differences between sympatric and allopatric populations have genetic basis. Differences between sympatric and allopatric populations evolved in place, not derived from founder groups already differing in the character. © 2019 McGraw-Hill Education.  Character Displacement Criteria (Part II) Variation in the character must have a known effect on use of resources. Must be demonstrated competition for the resource and competition must be directly correlated with character similarity. Differences in character cannot be explained by differences in resources available to each of the populations. © 2019 McGraw-Hill Education.  Review Intraspecific Competition. Plants, Planthopper. Competitive Exclusion and Niches. Darwin’s Finches. Mathematical and Laboratory Models. Lotka-Volterra, Paramecia and Tribolium. Competition and Niches. Plants, Barnacles, Small Rodents. Character Displacement. © 2019 McGraw-Hill Education.