Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings PowerPoint Lectures for Biology, Seventh Edition Neil Campbell & Jane Reece Lectures by Chris Romero Chapter 53 comm Ecology
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Overview: What Is a comm? biological community- pop’s of various spp living close enough for potential interaxn Animals & plants surrounding a watering hole in southern Africa are members of a savanna comm
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Concept 53.1: A community’s interactions include competition, predation, herbivory, symbiosis, & disease relationships b/w spp in a comm are interspecific interactions Interspecific interactions affect spp survival & reproduction Ex’s: competition, predation, herbivory, symbiosis (parasitism, mutualism, & commensalism), & disease
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Competition Interspecific competition- spp compete for a resource in short supply Strong competition can lead to competitive exclusion, local elimination of a competing spp
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings The Competitive Exclusion Principle The competitive exclusion principle- 2 spp competing for same limiting resources can’t occupy the same niche
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Ecological Niches ecological niche- total of a spp’ use of biotic & abiotic resources Ecologically similar spp can coexist in a comm if there are 1 or more significant diff's in their niches As a result of competition, a spp’ fundamental niche may differ from its realized niche
LE 53-2 Chthamalus fundamental niche High tide Low tide Ocean Chthamalus realized niche High tide Low tide Ocean Balanus realized niche Chthamalus Balanus
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Resource Partitioning Resource partitioning- differentiation of ecological niches, enabling similar spp to coexist in a comm
LE 53-3 A. insolitus usually perches on shady branches. A. ricordii A. insolitus A. christophei A. cybotes A. etheridgei A. aliniger A. distichus perches on fence posts & other sunny surfaces.
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Character Displacement Character displacement- tendency for char’s to be more divergent in sympatric pop's of 2 spp than in allopatric pop's of the same 2 spp An example is variation in beak size b/w pop's of 2 spp of Galapagos finches
LE 53-4 Beak depth Sympatric pop's G. fuliginosa G. fortis Santa María, San Cristóbal Los Hermanos Daphne G. fuliginosa, allopatric G. fortis, allopatric Beak depth (mm) Percentage of indiv's in each size class
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Predation Predation- 1 spp, (predator), kills & eats the other, the prey Some feeding adaptations of predators are claws, teeth, fangs, stingers, & poison
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Prey display various defensive adaptations Behavioral defenses include hiding, fleeing, self- defense, & alarm calls Animals also have morphological & physiological defense adaptations
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Cryptic coloration/camouflage- makes prey difficult to spot Video: Seahorse Camouflage Video: Seahorse Camouflage
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aposematic coloration- animals w/ effective chem defense often exhibit bright warning coloration Predators are particularly cautious in dealing w/ prey that display such coloration
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In some cases, a prey spp may gain significant protection by mimicking the appearance of another spp
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Batesian mimicry- palatable or harmless spp mimics an unpalatable or harmful model
LE 53-7 Hawkmoth larva Green parrot snake
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Müllerian mimicry- 2 or more unpalatable spp resemble each other
LE 53-8 Cuckoo bee Yellow jacket
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Herbivory Herbivory refers to an interaction in which an herbivore eats parts of a plant or alga It has led to evolution of plant mechanical & chemical defenses & adaptations by herbivores
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Parasitism In parasitism, 1 organism, the parasite, derives nourishment from another organism, its host, which is harmed in the process Parasitism exerts substantial influence on pop's & the structure of communities
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Disease Effects of disease on pop's & communities are similar to those of parasites 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 spp Video: Clownfish & Anemone Video: Clownfish & Anemone
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Commensalism In commensalism, 1 spp benefits & the other is apparently unaffected Commensal interactions are hard to document in nature because any close association of 2 spp likely affects both
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Interspecific Interactions & Adaptation Coevolution- reciprocal evolutionary adaptations of 2 interacting spp The term is often used too loosely in describing adaptations within a comm There is little evidence for true coevolution in most interspecific interactions
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Concept 53.2: Dominant & keystone spp exert strong controls on comm structure In general, a few spp in a comm exert strong control on that community’s structure 2 fundamental features of comm structure are spp diversity & feeding relationships
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings spp Diversity spp diversity of a comm is the variety of organisms that make up the comm It has 2 components: spp richness & relative abundance spp richness- total # of diff spp in the comm Relative abundance- proportion each spp represents of the total indiv's in the comm
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings 2 communities can have the same spp richness but a different relative abundance A comm w/ an even spp abundance is more diverse than one in which one or 2 spp are abundant & the remainder are rare
LE comm 1 A B C D A: 25% B: 25% C: 25% D: 25% comm 2 A: 80% B: 5% C: 5% D: 10%
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Trophic Structure Trophic structure- feeding relationships b/w organisms in a comm It is a key factor in comm dynamics Food chains link trophic levels from producers to top carnivores Video: Shark Eating a Seal Video: Shark Eating a Seal
LE Quaternary consumers Tertiary consumers Carnivore Secondary consumers Carnivore Primary consumers ZooplanktonHerbivore Primary producers Phytoplankton Plant A terrestrial food chain A marine food chain
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Food Webs food web- branching food chain w/ complex trophic interactions
LE Euphausids (krill) Carnivorous plankton Phyto- plankton Copepods Squids Elephant seals Fishes Birds Crab-eater seals Leopard seals Sperm whales Smaller toothed whales Baleen whales Humans
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Food webs can be simplified by isolating a portion of a comm that interacts very little w/ the rest of the comm
LE Zooplankton Fish larvae Fish eggs Sea nettle Juvenile striped bass
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 2 hypotheses attempt to explain food chain length: the energetic hypothesis & the dynamic stability hypothesis
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings The energetic hypothesis suggests that length is limited by inefficient energy transfer The dynamic stability hypothesis proposes that long food chains are less stable than short ones Most data support the energetic hypothesis
LE Productivity # of trophic links # of spp No. of trophic links No. of spp High (control) Medium Low
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings spp w/ a Large Impact Certain spp have a very large impact on comm structure Such spp are highly abundant or play a pivotal role in comm dynamics
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Dominant spp Dominant spp- most abundant or have the highest biomass They exert powerful control over the occurrence & distribution of other spp
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings One hypothesis suggests that dominant spp are most competitive in exploiting resources Another hypothesis is that they are most successful at avoiding predators
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Keystone spp In contrast to dominant spp, keystone spp- not necessarily abundant in a comm but exert strong control on a comm 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 spp in intertidal communities
LE Without Pisaster (experimental) w/ Pisaster (control) 1963 ’64’65 ’66 ’67 ’68’69 ’70 ’71 ’72 ’ # of spp present
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Observation of sea otter pop's & their predation shows how otters affect ocean communities
LE Sea otter abundance Otter # (% max. count) Sea urchin biomass Grams per 0.25 m Total kelp density # per 0.25 m Year Food chain before killer whale involvement in chain Food chain after killer whales started preying on otters
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Ecosystem “Engineers” (Foundation spp) Some organisms exert influence by causing physical changes in the environment that affect comm structure For example, beaver dams can transform landscapes on a very large scale
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Some foundation spp act as facilitators that have positive effects on survival & reproduction of some other spp in the comm
LE # of plant spp Conditions w/ Juncus Without Juncus Salt marsh w/ Juncus (foreground)
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Bottom-Up & Top-Down Controls The bottom-up model of comm organization proposes a unidirectional influence from lower to higher trophic levels In this case, presence or absence of mineral nutrients determines comm structure, including abundance of primary producers
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings The top-down model 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 experimental studies have shown that communities can shift periodically from bottom-up to top-down controls
LE Percentage of herbaceous plant cover Rainfall (mm)
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Pollution can affect comm dynamics Biomanipulation can help restore polluted communities
LE 53-UN1171 Polluted State Restored State Fish Abundant Rare Zooplankton Abundant Rare Algae Abundant Rare
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Concept 53.3: Disturbance influences spp diversity & composition Decades ago, most ecologists favored the view that communities are in a state of equilibrium Recent evidence of 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? disturbance- event that changes a comm, removes organisms from it, & alters resource availability Fire is a significant disturbance in most terrestrial ecosystems It is often a necessity in some communities
LE Before a controlled burn. A prairie that has not burned for several years has a high propor- tion of detritus (dead grass). During the burn. The detritus serves as fuel for fires. After the burn. Approximately one month after the controlled burn, virtually all of the biomass in this prairie is living.
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings intermediate disturbance hypothesis- moderate levels of disturbance can foster higher diversity than low levels of disturbance The large-scale fire in Yellowstone National Park in 1988 demonstrated that communities can often respond very rapidly to a massive disturbance
LE 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. One year after fire. This photo of the same general area taken the following year indicates how rapidly the com- munity 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 Human disturbance to communities usually reduces spp diversity Humans also prevent some naturally occurring disturbances, which can be important to comm structure
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Ecological Succession Ecological succession- seq of comm & ecosystem changes after a disturbance Primary succession- no soil exists/bare land Secondary succession- area still w/soil after a disturbance
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Early-arriving spp & later-arriving spp may be linked in 1 of 3 processes: – Early arrivals may facilitate appearance of later spp by making the environment favorable – They may inhibit establishment of later spp – They may tolerate later spp but have no impact on their establishment
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Retreating glaciers provide a valuable field- research opportunity for observing succession
LE McBride glacier retreating Canada Alaska Grand Pacific Gl Riggs Gl. Muir Gl. Plateau Gl. McBride Gl. Casement Gl Johns Hopkins Gl. Pleasant Is. Reid Gl Glacier Bay Miles 15 Kilometers
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 & soil characteristics
LE Pioneer stage, w/ fireweed dominant Dryas stage Spruce stage Nitrogen fixation by Dryas & alder increases the soil nitrogen content. Successional stage DryasPioneer Alder Spruce Soil nitrogen (g/m 2 )
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Concept 53.4: Biogeographic factors affect comm diversity 2 key factors correlated w/ a community’s spp diversity are geographic location & size
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Equatorial-Polar Gradients 2 key factors in equatorial-polar gradients of spp richness are probably evolutionary history & climate spp richness generally declines along an equatorial-polar gradient & is especially great in the tropics The greater age of tropical environments may account for the greater spp richness
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Climate is likely the primary cause of the latitudinal gradient in biodiversity 2 main climatic factors correlated w/ biodiversity: sun & water They can be considered together by measuring a community’s rate of evapotranspiration Evapotranspiration is evaporation of water from soil plus transpiration of water from plants
LE Trees Tree spp richness Vertebrate spp richness (log scale) , Actual evapotranspiration (mm/yr) Vertebrates 2,000 Potential evapotranspiration (mm/yr) 1,500 1,
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Area Effects The species-area curve quantifies the idea that, all other factors being equal, a larger geographic area has more spp A species-area curve of North American breeding birds supports this idea
LE # of spp (log scale) 1,000 Area (acres)
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Island Equilibrium Model spp richness on islands depends on island size, distance from the mainland, immigration, & extinction The equilibrium model of island biogeography maintains that spp richness on an ecological island levels off at a dynamic equilibrium point
LE Immigration & extinction rates # of spp on island Equilibrium # Immigration Rate of immigration or extinction Extinction Effect of island size # of spp on island Small island Immigration Rate of immigration or extinction Extinction Large island (large island) Immigration (small island) Extinction (large island) (small island) Effect of distance from mainland # of spp on island Far island Immigration Rate of immigration or extinction Extinction Near island (near island) Immigration (far island) Extinction (near island) (far island)
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Studies of spp richness on the Galápagos Islands support the prediction that spp richness increases w/ island size
LE Area of island (mi 2 ) (log scale) 400 # of plant spp (log scale) 1,
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Concept 53.5: Contrasting views of comm structure are the subject of continuing debate In the 1920s & 1930s, 2 views on comm structure emerged: the integrated hypothesis & the individualistic hypothesis
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Integrated & Individualistic Hypotheses integrated hypothesis- describes a comm as an assemblage of closely linked spp, locked into association by mandatory biotic interactions individualistic hypothesis- communities are loosely organized associations of independently distributed spp w/ the same abiotic requirements
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings The integrated hypothesis predicts that presence or absence of particular spp depends on presence or absence of other spp
LE 53-29a Environmental gradient (such as temperature or moisture) pop densities of indiv spp Integrated hypothesis
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings The individualistic hypothesis predicts that each spp is distributed according to its tolerance ranges for abiotic factors
LE 53-29b Environmental gradient (such as temperature or moisture) pop densities of indiv spp Individualistic hypothesis
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings In most actual cases, composition of communities seems to change continuously, w/ each spp more or less independently distributed
LE 53-29c Trees in the Santa Catalina Mountains # of plants per hectare Moisture gradient Wet Dry
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Rivet & Redundancy Models The rivet model suggests that all spp in a comm are linked in a tight web of interactions It also states that loss of even a single spp has strong repercussions for the comm The redundancy model proposes that if a spp is lost, other spp will fill the gap comm hypotheses & models represent extremes; most communities probably lie somewhere in the middle