Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings PowerPoint Lectures for Biology, Seventh Edition Neil Campbell and Jane Reece Lectures by Chris Romero Chapter 53 Community Ecology
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Overview: What Is a Community? A biological community – Is an assemblage of populations of various species living close enough for potential interaction
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings The various animals and plants surrounding this watering hole – Are all members of a savanna community in southern Africa Figure 53.1
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Concept 53.1: A community’s interactions include competition, predation, herbivory, symbiosis, and disease Populations are linked by interspecific interactions – That affect the survival and reproduction of the species engaged in the interaction
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Interspecific interactions – Can have differing effects on the populations involved Table 53.1
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Competition Interspecific competition – Occurs when species compete for a particular resource that is in short supply Strong competition can lead to competitive exclusion – The local elimination of one of the two competing species
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings The Competitive Exclusion Principle The competitive exclusion principle – States that two species competing for the same limiting resources cannot coexist in the same place
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Ecological Niches The ecological niche – Is the total of an organism’s use of the biotic and abiotic resources in its environment
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings The niche concept allows restatement of the competitive exclusion principle – Two species cannot coexist in a community if their niches are identical
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings However, ecologically similar species can coexist in a community – If there are one or more significant difference in their niches When Connell removed Balanus from the lower strata, the Chthamalus population spread into that area. The spread of Chthamalus when Balanus was removed indicates that competitive exclusion makes the realized niche of Chthamalus much smaller than its fundamental niche. RESULTS CONCLUSION Ocean Ecologist Joseph Connell studied two barnacle species Balanus balanoides and Chthamalus stellatus that have a stratified distribution on rocks along the coast of Scotland. EXPERIMENT In nature, Balanus fails to survive high on the rocks because it is unable to resist desiccation (drying out) during low tides. Its realized niche is therefore similar to its fundamental niche. In contrast, Chthamalus is usually concentrated on the upper strata of rocks. To determine the fundamental of niche of Chthamalus, Connell removed Balanus from the lower strata. Low tide High tide Chthamalus fundamental niche Chthamalus realized niche Low tide High tide Chthamalus Balanus realized niche Balanus Ocean Figure 53.2
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings As a result of competition – A species’ fundamental niche may be different from its realized niche
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings A. insolitus usually perches on shady branches. A. distichus perches on fence posts and other sunny surfaces. A. distichus A. ricordii A. insolitus A. christophei A. cybotes A. etheridgei A. alinigar Figure 53.3 Resource Partitioning Resource partitioning is the differentiation of niches – That enables similar species to coexist in a community
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings G. fortis Beak depth (mm) G. fuliginosa Beak depth Los Hermanos Daphne Santa María, San Cristóbal Sympatric populations G. fuliginosa, allopatric G. fortis, allopatric Percentages of individuals in each size class Figure 53.4 Character Displacement In character displacement – There is a tendency for characteristics to be more divergent in sympatric populations of two species than in allopatric populations of the same two species
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Predation Predation refers to an interaction – Where one species, the predator, kills and eats the other, the prey
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Feeding adaptations of predators include – Claws, teeth, fangs, stingers, and poison Animals also display – A great variety of defensive adaptations
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Cryptic coloration, or camouflage – Makes prey difficult to spot Figure 53.5
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Aposematic coloration – Warns predators to stay away from prey Figure 53.6
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings In some cases, one prey species – May gain significant protection by mimicking the appearance of another
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings In Batesian mimicry – A palatable or harmless species mimics an unpalatable or harmful model (a) Hawkmoth larva (b) Green parrot snake Figure 53.7a, b
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings In Müllerian mimicry – Two or more unpalatable species resemble each other (a) Cuckoo bee (b) Yellow jacket Figure 53.8a, b
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Herbivory Herbivory, the process in which an herbivore eats parts of a plant – Has led to the evolution of plant mechanical and chemical defenses and consequent adaptations by herbivores
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Parasitism In parasitism, one organism, the parasite – Derives its nourishment from another organism, its host, which is harmed in the process
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Parasitism exerts substantial influence on populations – And the structure of communities
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Disease The effects of disease on populations and communities – Is similar to that of parasites
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Pathogens, disease-causing agents – Are typically bacteria, viruses, or protists
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Mutualism Mutualistic symbiosis, or mutualism – Is an interspecific interaction that benefits both species Figure 53.9
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Commensalism In commensalism – One species benefits and the other is not affected Figure 53.10
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Commensal interactions have been difficult to document in nature – Because any close association between species likely affects both species
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Interspecific Interactions and Adaptation Evidence for coevolution – Which involves reciprocal genetic change by interacting populations, is scarce
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings However, generalized adaptation of organisms to other organisms in their environment – Is a fundamental feature of life
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Concept 53.2: Dominant and keystone species exert strong controls on community structure In general, a small number of species in a community – Exert strong control on that community’s structure
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Species Diversity The species diversity of a community – Is the variety of different kinds of organisms that make up the community – Has two components
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Species richness – Is the total number of different species in the community Relative abundance – Is the proportion each species represents of the total individuals in the community
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Two different communities – Can have the same species richness, but a different relative abundance Community 1 A: 25%B: 25%C: 25%D: 25% Community 2 A: 80%B: 5%C: 5%D: 10% D C B A Figure 53.11
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings A community with an even species abundance – Is more diverse than one in which one or two species are abundant and the remainder rare
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Trophic Structure Trophic structure – Is the feeding relationships between organisms in a community – Is a key factor in community dynamics
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Food chains Quaternary consumers Tertiary consumers Secondary consumers Primary consumers Primary producers Carnivore Herbivore Plant Carnivore Zooplankton Phytoplankton A terrestrial food chainA marine food chain Figure – Link the trophic levels from producers to top carnivores
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Food Webs A food web Humans Baleen whales Crab-eater seals Birds Fishes Squids Leopard seals Elephant seals Smaller toothed whales Sperm whales Carnivorous plankton Euphausids (krill) Copepods Phyto- plankton Figure – Is a branching food chain with complex trophic interactions
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Food webs can be simplified – By isolating a portion of a community that interacts very little with the rest of the community Sea nettle Fish larvae Zooplankton Fish eggs Juvenile striped bass Figure 53.14
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Limits on Food Chain Length Each food chain in a food web – Is usually only a few links long There are two hypotheses – That attempt to explain food chain length
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings The energetic hypothesis suggests that the length of a food chain – Is limited by the inefficiency of energy transfer along the chain
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings The dynamic stability hypothesis – Proposes that long food chains are less stable than short ones
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Most of the available data – Support the energetic hypothesis High (control) Medium Low Productivity No. of species No. of trophic links Number of species Number of trophic links Figure 53.15
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Species with a Large Impact Certain species have an especially large impact on the structure of entire communities – Either because they are highly abundant or because they play a pivotal role in community dynamics
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Dominant Species Dominant species – Are those species in a community that are most abundant or have the highest biomass – Exert powerful control over the occurrence and distribution of other species
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings One hypothesis suggests that dominant species – Are most competitive in exploiting limited resources Another hypothesis for dominant species success – Is that they are most successful at avoiding predators
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Keystone Species Keystone species – Are not necessarily abundant in a community – Exert strong control on a community by their ecological roles, or niches
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Field studies of sea stars – Exhibit their role as a keystone species in intertidal communities Figure 53.16a,b (a) The sea star Pisaster ochraceous feeds preferentially on mussels but will consume other invertebrates. With Pisaster (control) Without Pisaster (experimental) Number of species present ´64´65 ´66 ´67 ´68 ´69 ´70´71 ´72 ´73 (b) When Pisaster was removed from an intertidal zone, mussels eventually took over the rock face and eliminated most other invertebrates and algae. In a control area from which Pisaster was not removed, there was little change in species diversity.
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Observation of sea otter populations and their predation Figure Food chain before killer whale involve- ment in chain (a) Sea otter abundance (b) Sea urchin biomass (c) Total kelp density Number per 0.25 m Grams per 0.25 m 2 Otter number (% max. count) Year Food chain after killer whales started preying on otters – Shows the effect the otters have on ocean communities
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Ecosystem “Engineers” (Foundation Species) Some organisms exert their influence – By causing physical changes in the environment that affect community structure
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Beaver dams – Can transform landscapes on a very large scale Figure 53.18
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Some foundation species act as facilitators – That have positive effects on the survival and reproduction of some of the other species in the community Figure Salt marsh with Juncus (foreground) With Juncus Without Juncus Number of plant species Conditions
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Bottom-Up and Top-Down Controls The bottom-up model of community organization – Proposes a unidirectional influence from lower to higher trophic levels In this case, the presence or absence of abiotic nutrients – Determines community structure, including the abundance of primary producers
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings The top-down model of community organization – Proposes that control comes from the trophic level above In this case, predators control herbivores – Which in turn control primary producers
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Long-term experiment studies have shown – That communities can shift periodically from bottom-up to top-down Figure Rainfall (mm) Percentage of herbaceous plant cover
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Pollution – Can affect community dynamics But through biomanipulation – Polluted communities can be restored Fish Zooplankton Algae Abundant Rare Abundant Rare Polluted State Restored State
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Concept 53.3: Disturbance influences species diversity and composition Decades ago, most ecologists favored the traditional view – That communities are in a state of equilibrium
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings However, a recent emphasis on change has led to a nonequilibrium model – Which describes communities as constantly changing after being buffeted by disturbances
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings What Is Disturbance? A disturbance – Is an event that changes a community – Removes organisms from a community – Alters resource availability
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Fire – Is a significant disturbance in most terrestrial ecosystems – Is often a necessity in some communities (a) Before a controlled burn. A prairie that has not burned for several years has a high propor- tion of detritus (dead grass). (b) During the burn. The detritus serves as fuel for fires. (c) After the burn. Approximately one month after the controlled burn, virtually all of the biomass in this prairie is living. Figure 53.21a–c
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings The intermediate disturbance hypothesis – Suggests that moderate levels of disturbance can foster higher species diversity than low levels of disturbance
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings The large-scale fire in Yellowstone National Park in 1988 – Demonstrated that communities can often respond very rapidly to a massive disturbance Figure 53.22a, b (a) Soon after fire. As this photo taken soon after the fire shows, the burn left a patchy landscape. Note the unburned trees in the distance. (b) One year after fire. This photo of the same general area taken the following year indicates how rapidly the community began to recover. A variety of herbaceous plants, different from those in the former forest, cover the ground.
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Human Disturbance Humans – Are the most widespread agents of disturbance
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Human disturbance to communities – Usually reduces species diversity Humans also prevent some naturally occurring disturbances – Which can be important to community structure
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Ecological Succession Ecological succession – Is the sequence of community and ecosystem changes after a disturbance
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Primary succession – Occurs where no soil exists when succession begins Secondary succession – Begins in an area where soil remains after a disturbance
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Early-arriving species – May facilitate the appearance of later species by making the environment more favorable – May inhibit establishment of later species – May tolerate later species but have no impact on their establishment
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings McBride glacier retreating 0510 Miles Glacier Bay Pleasant Is. Johns Hopkins Gl. Reid Gl. Grand Pacific Gl. Canada Alaska Casement Gl. McBride Gl. Plateau Gl. Muir Gl. Riggs Gl. Retreating glaciers – Provide a valuable field-research opportunity on succession Figure 53.23
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Succession on the moraines in Glacier Bay, Alaska – Follows a predictable pattern of change in vegetation and soil characteristics Figure 53.24a–d (b) Dryas stage (c) Spruce stage (d) Nitrogen fixation by Dryas and alder increases the soil nitrogen content. Soil nitrogen (g/m 2 ) Successional stage Pioneer Dryas Alder Spruce (a) Pioneer stage, with fireweed dominant
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Concept 53.4: Biogeographic factors affect community diversity Two key factors correlated with a community’s species diversity – Are its geographic location and its size
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Equatorial-Polar Gradients The two key factors in equatorial-polar gradients of species richness – Are probably evolutionary history and climate
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Species richness generally declines along an equatorial-polar gradient – And is especially great in the tropics The greater age of tropical environments – May account for the greater species richness
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Climate – Is likely the primary cause of the latitudinal gradient in biodiversity
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings The two main climatic factors correlated with biodiversity – Are solar energy input and water availability (b) Vertebrates 500 1,000 1,500 2,000 Potential evapotranspiration (mm/yr) Vertebrate species richness (log scale) , Tree species richness (a) Trees Actual evapotranspiration (mm/yr) Figure 53.25a, b
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Area Effects The species-area curve quantifies the idea that – All other factors being equal, the larger the geographic area of a community, the greater the number of species
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings A species-area curve of North American breeding birds – Supports this idea Area (acres) Number of species (log scale) ,000 Figure 53.26
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Island Equilibrium Model Species richness on islands – Depends on island size, distance from the mainland, immigration, and extinction
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Figure 53.27a–c The equilibrium model of island biogeography maintains that – Species richness on an ecological island levels off at some dynamic equilibrium point Number of species on island (a) Immigration and extinction rates. The equilibrium number of species on an island represents a balance between the immigration of new species and the extinction of species already there. (b) Effect of island size. Large islands may ultimately have a larger equilibrium num- ber of species than small islands because immigration rates tend to be higher and extinction rates lower on large islands. Number of species on island (c) Effect of distance from mainland. Near islands tend to have larger equilibrium numbers of species than far islands because immigration rates to near islands are higher and extinction rates lower. Equilibrium number Small island Large islandFar island Near island Immigration Extinction Immigration Extinction Immigration (small island) (large island) (small island) Immigration Extinction Immigration (far island) (near island) (far island) Extinction Rate of immigration or extinction
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Studies of species richness on the Galápagos Islands – Support the prediction that species richness increases with island size The results of the study showed that plant species richness increased with island size, supporting the species-area theory. FIELD STUDY RESULTS Ecologists Robert MacArthur and E. O. Wilson studied the number of plant species on the Galápagos Islands, which vary greatly in size, in relation to the area of each island. CONCLUSION Area of island (mi 2 ) (log scale) Number of plant species (log scale) , Figure 53.28
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Concept 53.5: Contrasting views of community structure are the subject of continuing debate Two different views on community structure – Emerged among ecologists in the 1920s and 1930s
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Integrated and Individualistic Hypotheses The integrated hypothesis of community structure – Describes a community as an assemblage of closely linked species, locked into association by mandatory biotic interactions
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings The individualistic hypothesis of community structure – Proposes that communities are loosely organized associations of independently distributed species with the same abiotic requirements
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings The integrated hypothesis – Predicts that the presence or absence of particular species depends on the presence or absence of other species Population densities of individual species Environmental gradient (such as temperature or moisture) (a) Integrated hypothesis. Communities are discrete groupings of particular species that are closely interdependent and nearly always occur together. Figure 53.29a
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings The individualistic hypothesis – Predicts that each species is distributed according to its tolerance ranges for abiotic factors Population densities of individual species Environmental gradient (such as temperature or moisture) (b) Individualistic hypothesis. Species are independently distributed along gradients and a community is simply the assemblage of species that occupy the same area because of similar abiotic needs. Figure 53.29b
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings In most actual cases the composition of communities – Seems to change continuously, with each species more or less independently distributed Number of plants per hectare Wet Moisture gradientDry (c) Trees in the Santa Catalina Mountains. The distribution of tree species at one elevation in the Santa Catalina Mountains of Arizona supports the individualistic hypothesis. Each tree species has an independent distribution along the gradient, apparently conforming to its tolerance for moisture, and the species that live together at any point along the gradient have similar physical requirements. Because the vegetation changes continuously along the gradient, it is impossible to delimit sharp boundaries for the communities Figure 53.29c
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Rivet and Redundancy Models The rivet model of communities – Suggests that all species in a community are linked together in a tight web of interactions – Also states that the loss of even a single species has strong repercussions for the community
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings The redundancy model of communities – Proposes that if a species is lost from a community, other species will fill the gap
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings It is important to keep in mind that community hypotheses and models – Represent extremes, and that most communities probably lie somewhere in the middle