Chapter 53 (pgs. 1174 – 1196) Community Ecology AP minknow The difference between a fundamental niche and a realized niche The role of competitive exclusion in interspecific competition. The symbiotic relationships of parasitism, mutualism, and commensalism. The impact of keystone species on community structure. The difference between primary and secondary succession.

What Is a Community?  1.Explain the relationship between species richness and relative abundance.  2.Define and compare the individualistic hypothesis of H.A. Gleason and the interactive hypothesis of F.E. Clements with respect to communities. Interspecific Interactions and Community Structure 3.List four possible specific interactions and explain how the relationships affect the population densities of the two species.  4.Explain how interspecific competition may affect community structure.  5.Describe the competitive exclusion principle and explain how competitive exclusion may affect community structure.  6.Define an ecological niche and restate the competitive exclusion principle using the niche concept.  7.Explain how resource partitioning can affect species diversity.  8.Define and compare predation, herbivory, and parasitism.  9.Relate some specific predatory adaptations to the properties of the prey.  10.Describe the defense mechanisms that evolved in plants to reduce predation by herbivores. 

11.Explain how cryptic coloration and warning coloration aid an animal in avoiding predators.  12.Distinguish between Batesian mimicry and Müllerian mimicry.  13.Describe how predators use mimicry to obtain prey.  14.Distinguish among endoparasites, ectoparasites, and pathogens.  15.Distinguish among parasitism, mutualism, and commensalism.  16.Distinguish between a food chain and a food web. Describe the factors that transform food chains into food webs.  17.Describe two ways to simplify food webs.  18.Summarize two hypotheses that explain why food chains are relatively short.  19.Explain how dominant and keystone species exert strong control on community structure. Give several examples of each.  20.Describe and distinguish between the bottom-up and top-down models of community organization. Also describe some models that are intermediate between those two extremes.

Disturbance and Community Structure 21.Describe how disturbances affect community structure and composition. Illustrate this point with several well-studied examples.  22.Give examples of humans as widespread agents of disturbance.  23.Describe and distinguish between primary and secondary succession.  24.Describe and distinguish among facilitation, inhibition, and toleration.  25.Describe the process and pattern of succession on moraines in Glacier Bay. Biogeographic Factors Affecting the Biodiversity of Communities 26.Describe and distinguish between species richness and relative abundance.  27.Describe the data necessary to measure biodiversity.  28.Describe and explain how species richness varies along the equatorial-polar gradient.  29.Define the species-area curve.  30.Explain how species richness on islands varies according to island size and distance from the mainland.

What Is a Community? 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

Populations are linked by interspecific interactions 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 These interaction can have differing effects on the populations involved

Competition Interspecific competition Click on picture to watch movie 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 The competitive exclusion principle States that two species competing for the same limiting resources cannot coexist in the same place

Ecological Niches Habitat - the area where an organism lives, including the biotic and abiotic factors that affect the organism. Resources - any necessity of life, such as water, nutrients, light, food, or space. Habitat + Resources = ????? The ecological niche Is the total of an organism’s use of the biotic and abiotic resources in its environment

Warbler Niches Can you have two separate organisms occupying the same exact niche???

NO 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 Chthamalus Balanus realized niche Balanus

Resource Partitioning Resource partitioning is the differentiation of niches That enables similar species to coexist in a community 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

Character Displacement 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 40 20 8 10 12 14 16 Figure 53.4 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 Sympatric population – geographically overlapping Allopatric population – geographically isolated

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

Defensive Adaptations Cryptic coloration Aposematic coloration Batesian mimicry Mullerian mimicry

Cryptic coloration, or camouflage Makes prey difficult to spot Figure 53.5

Aposematic coloration Warns predators to stay away from prey Poison arrow frog Figure 53.6

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

In Müllerian mimicry Two or more unpalatable species resemble each other (a) Cuckoo bee (b) Yellow jacket Figure 53.8a, b

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

Community Interactions Symbiosis – any relationship in which two species live closely together. There are three types of Symbiosis Parasitism Disease Mutualism Commensalism

Parasitism In parasitism, one organism, the parasite Derives its nourishment from another organism, its host, which is harmed in the process

Parasitism Parasitism exerts substantial influence on populations And the structure of communities Parasite Host Endoparasites Ectoparasites Parasitoidism

Disease The effects of disease on populations and communities Is similar to that of parasites Pathogens, disease-causing agents Are typically bacteria, viruses, or protists

Mutualism Mutualistic symbiosis, or mutualism Is an interspecific interaction that benefits both species Figure 53.9

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 Figure 53.10

Interspecific Interactions and Adaptation Evidence for coevolution Which involves reciprocal genetic change by interacting populations, is scarce However, generalized adaptation of organisms to other organisms in their environment Is a fundamental feature of life

In general, a small number of species in a community 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 Dominant Species – Those species in a community that have the highest abundance or highest biomass. These species exert a powerful control over the occurrence and distribution of other species. Keystone Species – A species that is not necessarily abundant in a community yet exerts strong control on community structure by the nature of its ecological role or niche

Species Diversity The species diversity of a community Is the variety of different kinds of organisms that make up the community Has two components 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

Species Diversity 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 A community with an even species abundance Is more diverse than one in which one or two species are abundant and the remainder rare

Trophic Structure Trophic structure Is the feeding relationships between organisms in a community Is a key factor in community dynamics We can look at trophic structure through Food Chains Food Webs

A terrestrial food chain Food chains Quaternary consumers Tertiary consumers Secondary consumers Primary consumers Primary producers Carnivore Herbivore Plant Zooplankton Phytoplankton A terrestrial food chain A marine food chain Figure 53.12 Link the trophic levels from producers to top carnivores Help to show the flow of energy through an ecosystem

Smaller toothed whales Food Webs Humans Baleen whales Crab-eater seals Birds Fishes Squids Leopard seals Elephant Smaller toothed whales Sperm whales Carnivorous plankton Euphausids (krill) Copepods Phyto- plankton Figure 53.13 Is a branching food chain with complex trophic interactions

Food Webs 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

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

Limits on Food Chain Lengths 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 1 2 3 4 5 6 Figure 53.15 Reduction of energy input in a tree-hole community (Queensland, Australia) had a direct affect on the length of the food chain

Species with a Large Impact Certain species have an especially large impact on the structure of entire communities Either because they are highly abundant r because they play a pivotal role in community dynamics Dominant Species Keystone Species

Dominant 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

Number of species present Keystone Species Field studies of sea stars Exhibit their role as a keystone species in intertidal communities (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 5 10 15 20 1963 ´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.

Otter number (% max. count) Keystone Species Observation of sea otter populations and their predation Figure 53.17 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 m2 1972 1985 1989 1993 1997 2 4 6 8 10 100 200 300 400 Grams per 0.25 m2 Otter number (% max. count) 40 20 60 80 Year Food chain after killer whales started preying on otters Shows the effect the otters have on ocean communities

Ecosystem “Engineers” (Foundation Species) Some organisms exert their influence By causing physical changes in the environment that affect community structure

Foundation Species Some foundation species act as facilitators Salt marsh with Juncus (foreground) With Juncus Without Juncus Number of plant species 2 4 6 8 Conditions Some foundation species act as facilitators That have positive effects on the survival and reproduction of some of the other species in the community

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

Bottom-Up and Top-Down Controls 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

Long-term experiment studies have shown That communities can shift periodically from bottom-up to top-down 100 200 300 400 Rainfall (mm) 25 50 75 Percentage of herbaceous plant cover Bottom-Up Rainfall determines community controls in this Chilean desert comm. (Non-El Nino) Dry (El Nino) Wet Top-Down

Pollution But through biomanipulation Can affect community dynamics Polluted communities can be restored Fish Zooplankton Algae Abundant Rare Polluted State Restored State

53.3: 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

What Is Disturbance? A disturbance Is an event that changes a community Removes organisms from a community Alters resource availability

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. The intermediate disturbance hypothesis Suggests that moderate levels of disturbance can foster higher species 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 (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. Figure 53.22a, b

Human Disturbance Humans Human disturbance to communities 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

Ecological Succession Ecosystems are constantly in flux. Ecological Succession – is the series of predictable changes that occurs in an ecosystem over time. Primary succession Secondary succession

Primary Succession Occurs on surfaces where no soil exists, usually after a volcanic eruption. (receding glaciers) 1. Bare rock community is populated by an pioneer species (first species to populate an area). Usually lichens (fungus and alga). 2. Pioneer species help to form soil and puts nutrients into soil. 3. Plants begin to grow  then off to the races

Secondary Succession Occurs in an community where everything has been removed but the soil. What could cause the process of primary succession to begin?

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/m2) Successional stage Pioneer Dryas Alder Spruce 10 20 30 40 50 60 (a) Pioneer stage, with fireweed dominant

Further Your Information Read 53.4 and 53.5 Page 1175  Page 1180