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 54 Community Ecology

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings A biological community – Is an assemblage of populations of various species living close enough for potential interaction The various animals and plants surrounding this watering hole – Are all members of a savanna community in southern Africa

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings 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 Interspecific interactions – Can have differing effects on the populations involved

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 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 The niche concept allows restatement of the competitive exclusion principle – Two species cannot coexist in a community if their niches are identical However, ecologically similar species can coexist in a community – If there are one or more significant difference in their niches As a result of competition – A species’ fundamental niche may be different from its realized niche 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

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 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 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 G. fortis Beak depth (mm) G. fuliginosa Beak depth Los Hermanos Daphne Santa María, San Cristóbal Sympatric population s G. fuliginosa, allopatric G. fortis, allopatric Percentages of individuals in each size class

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 Feeding adaptations of predators include – Claws, teeth, fangs, stingers, and poison Animals also display – A great variety of defensive adaptations Cryptic coloration, or camouflage – Makes prey difficult to spot Aposematic coloration – Warns predators to stay away from prey

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 In Batesian mimicry – A palatable or harmless species mimics an unpalatable or harmful model In Müllerian mimicry – Two or more unpalatable species resemble each other (a) Hawkmoth larva (b) Green parrot snake (a) Cuckoo bee (b) Yellow jacket

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 Parasitism exerts substantial influence on populations – And the structure of communities

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Mutualism Mutualistic symbiosis, or mutualism – Is an interspecific interaction that benefits both species

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Commensalism In commensalism – One species benefits and the other is not affected 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 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 The species diversity of a community – Is the variety of different kinds of organisms that make up the community 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 Two different communities – Can have the same species richness, but a different relative abundance A community with an even species abundance – Is more diverse than one in which one or two species are abundant and the remainder rare Community 1 A: 25%B: 25%C: 25%D: 25% Community 2 A: 80%B: 5%C: 5%D: 10% D C B A

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Quaternary consumers Tertiary consumers Secondary consumers Primary consumers Primary producers Carnivore Herbivore Plant Carnivore Zooplankton Phytoplankton A terrestrial food chainA marine food chain Trophic Structure Trophic structure – Is the feeding relationships between organisms in a community – Is a key factor in community dynamics Food chains Link the trophic levels from producers to top carnivores A food web Is a branching food chain with complex trophic interactions Humans Baleen whales Crab- eater seals Birds Fishes Squids Leopard seals Elephant seals Smaller toothed whales Sperm whales Carnivor ous plankton Euphaus ids (krill) Copepods Phyto- plankton

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

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 The energetic hypothesis suggests that the length of a food chain – Is limited by the inefficiency of energy transfer along the chain The dynamic stability hypothesis – Proposes that long food chains are less stable than short ones Most of the available data – Support the energetic hypothesis

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 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 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 Observation of sea otter populations and their predation Food chain before killer whale involvement 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 Beaver dams – Can transform landscapes on a very large scale Some foundation species act as facilitators – That have positive effects on the survival and reproduction of some of the other species in the community 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 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 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 Disturbance influences species diversity and composition Decades ago, most ecologists favored the traditional view – That communities are in a state of equilibrium However, a recent emphasis on change has led to a nonequilibrium model – Which describes communities as constantly changing after being buffeted by disturbances 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 proportion 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.

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 (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 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 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

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 (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 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 Species richness generally declines along an equatorial-polar gradient – And is especially great in the tropics The greater age of tropical environment may account for the greater species richness Climate is likely the primary cause of the latitudinal gradient in biodiversity 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)

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 A species-area curve of North American breeding birds – Supports this idea Area (acres) Number of species (log scale) ,000

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 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 number 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 Community ecology is useful for understanding pathogen life cycles and controlling human disease. Pathogens can alter community structure quickly and extensively. Coral reef communities are particularly susceptible to the influence of pathogens. Pathogens also influence community structure in terrestrial ecosystems. human activities are transporting pathogens around the world at unprecedented rates Zoonotic pathogens are transferred from other animals to humans, either through direct contact with an infected animal or by means of an intermediate species called a vector Understanding parasite life cycles enables scientists to devise ways to control zoonotic diseases