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Explore the various types of species interactions, including competition, predation, mutualism, and more, and how they impact population dynamics, species distributions, and evolutionary changes.
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Ecology • Chapter 44-46 Lecture • AP Biology • 2013
44 Ecological and EvolutionaryConsequences of SpeciesInteractions
Concept 44.1 Interactions between Species May BePositive, 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.
Concept 44.1 Interactions between Species May BePositive, 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.
Figure 44.1 Types of Interspecific Interactions (Part 2) Green plants compete for light. The leaves of tall trees have reduced light available to the plants growing on the forest floor.
Concept 44.1 Interactions between Species May BePositive, 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. A parasitic organism consumes part of a host individual but usually does not kill it Kills and consumes individuals of another species Animal consumes part of or all of a plant
Concept 44.1 Interactions between Species May BePositive, 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 44.1 Interactions between Species May BePositive, 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 BePositive, 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.
Concept 44.1 Interactions between Species May BePositive, Negative, or Neutral Relationships between species do not always fit perfectly into these categories. Fish that live with sea anemones escape predation by hiding in the anemone tentacles. Effects of this on the anemones is unclear. Do the fish steal some of their prey? Do they get nutrients from fish feces? It may depend on the availability of nutrients.
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 resource availability decreases as population density increases.
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. P. bursaria can feed on bacteria in the low-oxygen sediment layer at the bottom of culture flasks. P. bursaria has symbiotic algae that provides it with oxygen from photosynthesis.
Figure 44.5 Resource Partitioning Can Result in Intraspecific Competition Being Greater than Interspecific Competition
Leaf Cutting Ants and Fungi Watch. Can you explain their mutualistic existence?
Answer to Opening Question In the mutualism between leaf-cutter ants and the fungus they cultivate, both species gain nutrition from the interaction. Ants also disperse the fungus and protect it from pathogens. It may have started when ants began eating the fungi growing on refuse in their nests. Ants that provided better growing conditions had more fungus to eat and thus higher fitness.
Answer to Opening Question Fungi that provided ants with more nutrients were more likely to be propagated by ants. The ants expanded their food base by feeding leaves to the fungi (ants can’t digest the leaves). The fungi then had access to food they would not be able to use if ants did not chop it up for them.
Answer to Opening Question Leaf-cutter ants and their fungi have been very successful: They are major herbivores in the Neotropics, and have expanded into dry environments that are normally hostile to fungi.
45 Ecological Communities
Concept 45.1 Communities Contain Species That Colonize and Persist Community—a group of species that coexist and interact with one another within a defined area Biologists may designate community boundaries based on natural boundaries (e.g., the edge of a pond) or arbitrarily. They may restrict study to certain groups (e.g., the bird community).
Concept 45.1 Communities Contain Species That Colonize and Persist Communities are characterized by species composition; that is, which species they contain and the relative abundances of those species. A species can occur in a location only if it is able to colonize and persist there. A community contains those species that have colonized minus those that have gone extinct locally.
Concept 45.1 Communities Contain Species That Colonize and Persist Local extinctions can occur for many reasons: Species unable to tolerate local conditions A resource may be lacking Exclusion by competitors, predators, or pathogens Population size too small; no reproduction
Concept 45.1 Communities Contain Species That Colonize and Persist In 1883 the volcano on Krakatau erupted, killing everything on the island. Scientists studied the return of living organisms. Within 3 years, seeds of 24 plant species had reached the island. Later, as trees grew up, some pioneering plant species that require high light levels disappeared from the island’s now-shady interior. Species composition continues to change as new species colonize and others go extinct.
Concept 45.2 Communities Change over Space and Time Species often replace one another in a predictable sequence called succession.
Concept 45.3 Trophic Interactions Determine HowEnergy and Materials Move through Communities Each species in a community has a unique niche. This concept refers to the environmental tolerances of a species, which define where it can live. Also refers to the ways a species obtains energy and materials and to patterns of interaction with other species in the community.
Concept 45.3 Trophic Interactions Determine HowEnergy and Materials Move through Communities Consumer–resource, or trophic interactions cause energy and materials to flow through a community. Trophic levels—feeding positions Primary producers, or autotrophs, convert solar energy into a form that can be used by the rest of the community.
Concept 45.3 Trophic Interactions Determine HowEnergy and Materials Move through Communities Heterotrophs get energy by breaking apart organic compounds that were assembled by other organisms. Primary consumers (herbivores) eat primary producers. Secondary consumers (carnivores) eat herbivores. Tertiary consumers eat secondary consumers.
Concept 45.3 Trophic Interactions Determine HowEnergy and Materials Move through Communities Omnivores feed from multiple trophic levels. Decomposers, or detritivores, feed on waste products or dead bodies of organisms. Decomposers are responsible for recycling of materials; they break down organic matter into inorganic components that primary producers can absorb.
Concept 45.3 Trophic Interactions Determine HowEnergy and Materials Move through Communities Trophic interactions are shown in diagrams called food webs. Arrows indicate the flow of energy and materials —who eats whom.
Concept 45.3 Trophic Interactions Determine HowEnergy and Materials Move through Communities Gross primary productivity (GPP)—total amount of energy that primary producers convert to chemical energy. Net primary productivity (NPP)—energy contained in tissues of primary producers and is available for consumption. Change in biomass of primary producers (dry mass) per unit of time is an approximation for NPP.
Concept 45.3 Trophic Interactions Determine HowEnergy and Materials Move through Communities Ecological efficiency is about 10%: Only about 10% of the energy in biomass at one trophic level is incorporated into the biomass of the next trophic level. This loss of available energy at successive levels limits the number trophic levels in a community.
Concept 45.3 Trophic Interactions Determine HowEnergy and Materials Move through Communities Ecological efficiency is low because: Not all the biomass at one trophic level is ingested by the next one. Some ingested matter is indigestible and is excreted as waste. Organisms use much of the energy they assimilate to fuel their own metabolism.
Concept 45.4 Species Diversity Affects Community Function Species diversity has two components: Species richness—the number of species in the community. Species evenness—the distribution of species’ abundances
Figure 45.9 Species Richness and Species Evenness Contribute to Diversity Less diverse than B because it has an uneven distribution of the 4 species Less diverse than B because it contains 3 equally abundant species rather than 4 Most Diverse!
46 The Global Ecosystem
Concept 46.1 Climate and Nutrients Affect Ecosystem Function Ecosystem—an ecological community plus the abiotic environment with which it exchanges energy and materials. Ecosystems are linked by processes and material movements.
Concept 46.2 Biological, Geological, and Chemical ProcessesMove Materials through Ecosystems All the materials in the bodies of living organisms are ultimately derived from abiotic sources. Primary producers take up elements from inorganic pools and accumulate them as biomass. Trophic interactions pass the elements on to heterotrophs. Decomposers break down the dead and waste matter pool into elements that are available again for uptake by primary producers.
4 Biogeochemical Cycles • Water Cycle • Nitrogen Cycle • Carbon Cycle • Phosphorus Cycle
WATER CYCLE The global water (hydrological) cycle: Water is essential for life; makes up 70% of living biomass. Flowing water is an erosion agent and transports sediment—moves material around the planet. Because of high heat capacity, water redistributes heat as it circulates through the oceans and atmosphere.
Concept 46.3 Certain Biogeochemical CyclesAre Especially Critical for Ecosystems Solar-powered evaporation moves water from ocean and land surfaces into the atmosphere. The energy is released again as heat when water vapor condenses.
WATER CYCLE Humans affect the water cycle by changing land use: Reduced vegetation (deforestation, cultivation, etc.) reduces precipitation retained in soil and increases amount that runs off. Groundwater pumping depletes aquifers, brings water to surface where it evaporates. Climate warming will melt ice caps and glaciers and cause sea level rise and increased evaporation. Water vapor is a greenhouse gas.
NITROGEN CYCLE The global nitrogen cycle: Involves chemical transformations. N2 gas is 78% of the atmosphere, but most organisms cannot use this form. Nitrogen fixation: some microbes can break the strong triple bond and reduce N2 to ammonium (NH4+).
