Transcript PPT File
44 Ecological and Evolutionary Consequences of Species Interactions Chapter 44 Ecological and Evolutionary Consequences of Species Interactions Key Concepts • 44.1 Interactions between Species May Be Positive, Negative, or Neutral • 44.2 Interspecific Interactions Affect Population Dynamics and Species Distributions • 44.3 Interactions Affect Individual Fitness and Can Result in Evolution • 44.4 Introduced Species Alter Interspecific Interactions Concept 44.1 Interactions between Species May Be Positive, Negative, or Neutral Interspecific interactions (between individuals of different species) affect population densities, species distributions, and ultimately lead to evolutionary changes. The interactions can be beneficial or detrimental to either of the species. Figure 44.1 Types of Interspecific Interactions (Part 1) Concept 44.1 Interactions between Species May Be Positive, Negative, or Neutral Interspecific competition refers to –/– interactions Members of two or more species use the same resource. At any one time there is often one limiting resource in the shortest supply relative to demand. Concept 44.1 Interactions between Species May Be Positive, Negative, or Neutral Consumer–resource interactions—organisms get their nutrition by eating other living organisms. +/– interactions—the consumer benefits while the consumed organism loses Includes predation, herbivory, and parasitism. Figure 44.1 Types of Interspecific Interactions Competition Figure 44.1 Types of Interspecific Interactions Commensalism Concept 44.1 Interactions between Species May Be Positive, Negative, or Neutral Commensalism—one species benefits while the other is unaffected (+/0 interaction). • Brown-headed cowbird follows grazing cattle and bison, foraging on insects flushed from the vegetation. • Cattle convert plants into dung, which dung beetles can use. Dung beetles disperse other dung-living organisms such as mites and nematodes, which attach themselves to the bodies of the beetles. Concept 44.1 Interactions between Species May Be Positive, Negative, or Neutral Amensalism—one species is harmed while the other is unaffected (–/0 interactions). Tend to be more accidental than other relationships. Example: a herd of elephants that crush plants and insects while moving through a forest. Figure 44.1 Types of Interspecific Interactions Mutualism Concept 44.1 Interactions between Species May Be Positive, Negative, or Neutral Mutualism benefits both species: +/+ interaction Examples: • Leaf-cutter ants and the fungi they cultivate • Plants and pollinating or seed-dispersing animals • Humans and bifidobacteria in our guts • Plants and mycorrhizal fungi • Lichens • Corals and dinoflagellates Concept 44.3 Interactions Affect Individual Fitness and Can Result in Evolution All mutualisms involve the exchange of resources and services. The fitness effect of the mutualism can vary depending on environmental conditions. Example: Mycorrhizae benefit plants in nutrientpoor soils, but can be a liability in nutrient-rich soils, where the cost of feeding the mycorrhizae outweighs their value in nutrient uptake. Concept 44.3 Interactions Affect Individual Fitness and Can Result in Evolution Cheating in mutualisms: Some flowers mimic the form and smell of female insects and are pollinated when males attempt to copulate with them. Some bees bite holes in the base of flowers and eat the nectar without pollinating the flower. Concept 44.2 Interspecific Interactions Affect Population Dynamics and Species Distributions Density-dependent population growth reflects intraspecific (within-species) interactions among individuals in a population. They are usually detrimental because per capita resources decreases as population density increases. Interspecific interactions (between members of different species) also modify per capita growth rates. They can lead to extinction. Interspecific competition —effect of the other species would be subtracted (prey) or added (predator) in the per capita growth rate, depending on the interaction. Concept 44.2 Interspecific Interactions Affect Population Dynamics and Species Distributions Populations show different dynamics in the presence or absence of other species. This was demonstrated in classic experiments with species of Paramecium. Figure 44.3 Interspecific Competition Can Lead to Extinction Concept 44.2 Interspecific Interactions Affect Population Dynamics and Species Distributions Resource partitioning—different ways of using a resource. Example: Paramecium caudatum can coexist with P. bursaria. Why? P. bursaria feed on bacteria in the lowoxygen sediment layer at the bottom of culture flasks. P. bursaria has symbiotic algae that provides it with oxygen from photosynthesis. Concept 44.2 Interspecific Interactions Affect Population Dynamics and Species Distributions Conclusions from the Paramecium studies, and from mathematical models: • Presence of a competitor always reduces population growth rate. • When two species coexist, they have lower equilibrium population densities than either would alone. • In some cases, competition causes one species to go extinct. Concept 44.2 Interspecific Interactions Affect Population Dynamics and Species Distributions Interspecific interactions can affect the distributions of species. Competitive interactions can restrict the habitats in which species occur. Two barnacle species compete for space on the rocky shorelines of the North Atlantic, with no overlap between zones occupied. A classic experiment removed each species and observed response of the other species. Figure 44.4 Interspecific Competition Can Restrict Distributions Concept 44.2 Interspecific Interactions Affect Population Dynamics and Species Distributions Two competitors can coexist • when each species suppresses its own per capita growth rate more than it suppresses the per capita growth rate of its competitor. A species has a growth advantage when it is at a low density and its competitor is at a high density. Huh? • This rarity advantage prevents the species from decreasing to zero. Result is coexistence. • Example prey can become harder to find as they become rare. Hide in best locals, have more resources per capita. Figure 44.5 Resource Partitioning Can Result in Intraspecific Competition Being Greater than Interspecific Competition When 2 species of birds differ in resource use, individuals will have a greater affect on resource availability to the same species than to the other species Concept 44.3 Interactions Affect Individual Fitness and Can Result in Evolution Species interactions can affect individual fitness. Phenotypes that gain the most from a positive interaction or suffer least from a negative interaction will increase in frequency in the population, and the population will evolve. Natural selection will favor the trait and its frequency will increase in the population (directional selection). More resources will be available for this phenotype, increasing the carrying capacity. Concept 44.3 Interactions Affect Individual Fitness and Can Result in Evolution Resource partitioning as an evolutionary response: Finch species in the Galápagos Islands have varying beak sizes; beak sizes match sizes of available seeds. Figure 44.6 Resource Paritioning Allows Competitors to Coexist (Part 1) Homework Answer the questions that follow Figure 44.6 Resource Paritioning Allows Competitors to Coexist (Part 2) Figure 44.6 Resource Paritioning Allows Competitors to Coexist (Part 3) Concept 44.3 Interactions Affect Individual Fitness and Can Result in Evolution In one finch species on the Galápagos Islands, small individuals feed more on nectar, larger individuals feed more on seeds. On islands where carpenter bees are present and compete for nectar, the finches tend to be larger and eat more seeds. The finch resource use has diverged from their bee competitors on islands where they coexist. Figure 44.7 Finch Morphology Evolves in Response to Competition with Carpenter Bees (Part 2) Concept 44.3 Mechanisms for Survival, Fooling, Foiling, Fighting Strategies of resource species: • Use speed, size, or weapons to thwart predators. • Hide or use camouflage • Mimic unpalatable species • Sessile species have thick armor or are nonnutritive or poisonous. Figure 44.8 Defense Mechanisms and “Arms Races” (Part 1) E. Balteatus is a harmless hoverfly. It gains protection by mimicking V. vulgaris a stinging wasp which predators avoid Concept 44.3 Interactions Affect Individual Fitness and Can Result in Evolution Strategies of consumers: • Greater speed, size, or strength • Keen senses • Armor-piercing or crushing tools • Means of detoxifying poisons Concept 44.3 Interactions Affect Individual Fitness and Can Result in Evolution Plants produce a variety of toxic chemicals against herbivores and pathogens. Some of these chemicals we use as spices, etc.: black pepper, chili peppers, caffeine. Herbivores evolve ways to deal with the chemicals. Concept 44.4 Introduced Species Alter Interspecific Interactions Species introduced into a region where their natural enemies are absent may reach very high population densities. They may become invasive—reproduce rapidly and spread widely, and have negative impacts on native species. Concept 44.4 Invasive species are spread in many ways: Marine species have spread by being carried in ballast water on ships. Terrestrial species are carried unknowingly by humans as we have moved around the globe. Deliberate introductions (e.g., Europeans brought many plants and animals to their new homes). Species are still being transported— ornamental plants, exotic pets, etc. Concept 44.4 Introduced Species Alter Interspecific Interactions Invasive species can harm native species in various ways: Invasive flowering plants can alter relationships between native plants and their pollinators. Purple loosestrife was introduced to North America in the early 1800s and now dominates wetlands. It competes with the native Lythrum alatum, which receives fewer visits from pollinators and produces fewer seeds when purple loosestrife is present. Concept 44.4 Some invasive species cause extinction of native species. Example: A sac fungus blight caused extinction of American chestnut trees. Chestnuts have been replaced by oaks. Chestnut trees produced consistent nut crops each year, but acorn production varies greatly, contributing to yearly fluctuations in rodents, ticks, and Lyme disease in the northeastern U.S. Remember the chpt. 43 case study? Concept 44.4 Introduced Species for Pest Control A weevil was introduced to North America to control invasive musk thistle. When abundance of the thistle declined, the weevil began eating seeds of native thistle species. The weevil has become a competitor of native insects that eat thistles.