CAMPBELL BIOLOGY IN FOCUS © 2014 Pearson Education, Inc. Urry Cain Wasserman Minorsky Jackson Reece Lecture Presentations by Kathleen Fitzpatrick and Nicole Tunbridge 41 Species Interactions

© 2014 Pearson Education, Inc. In a given community, what types of interactions could different organisms have with each other?

© 2014 Pearson Education, Inc. Concept 41.1: Interactions within a community may help, harm, or have no effect on the species involved  Ecologists call relationships between species in a community interspecific interactions  Examples are competition, predation, herbivory, symbiosis (parasitism, mutualism, and commensalism), and facilitation  Interspecific interactions can affect the survival and reproduction of each species, and the effects can be summarized as positive (  ), negative (−), or no effect (0)

© 2014 Pearson Education, Inc. Competition  Interspecific competition (−/− interaction) occurs when species compete for a resource that limits their growth or survival

© 2014 Pearson Education, Inc. Define competitive exclusion.

© 2014 Pearson Education, Inc. Competitive Exclusion  Strong competition can lead to competitive exclusion, local elimination of a competing species  The competitive exclusion principle states that two species competing for the same limiting resources cannot coexist in the same place

© 2014 Pearson Education, Inc. How might two organisms occupying the same niche affect competition?

© 2014 Pearson Education, Inc. Ecological Niches and Natural Selection  Evolution is evident in the concept of the ecological niche, the specific set of biotic and abiotic resources used by an organism  An ecological niche can also be thought of as an organism’s ecological role  Ecologically similar species can coexist in a community if there are one or more significant differences in their niches

© 2014 Pearson Education, Inc.  Resource partitioning is differentiation of ecological niches, enabling similar species to coexist in a community

© 2014 Pearson Education, Inc. Figure 41.2 A. ricordii A. distichus perches on fence posts and other sunny surfaces. A. insolitus usually perches on shady branches. A. insolitus A. aliniger A. distichus A. cybotes A. etheridgei A. christophei

© 2014 Pearson Education, Inc.  A species’ fundamental niche is the niche potentially occupied by that species  A species’ realized niche is the niche actually occupied by that species  As a result of competition, a species’ fundamental niche may differ from its realized niche  For example, the presence of one barnacle species limits the realized niche of another species

© 2014 Pearson Education, Inc. Character Displacement  Character displacement is a tendency for characteristics to be more divergent in sympatric populations (geographically overlapping) of two species than in allopatric (geographically separate) populations of the same two species  An example is variation in beak size between populations of two species of Galápagos finches

© 2014 Pearson Education, Inc. Predation  Predation (  /− interaction) refers to an interaction in which one species, the predator, kills and eats the other, the prey  Some feeding adaptations of predators are claws, teeth, stingers, and poison

© 2014 Pearson Education, Inc. Describe some evolutionary adaptions prey might have acquired to avoid being eaten?

© 2014 Pearson Education, Inc. Figure 41.5 (a) Cryptic coloration Canyon tree frog (b) Aposematic coloration (c) Batesian mimicry: A harmless species mimics a harmful one. (d) Müllerian mimicry: Two unpalatable species mimic each other. Poison dart frog Nonvenomous hawkmoth larva Venomous green parrot snake Cuckoo bee Yellow jacket

© 2014 Pearson Education, Inc. Herbivory  Herbivory (  /− interaction) refers to an interaction in which an herbivore eats parts of a plant or alga  In addition to behavioral adaptations, some herbivores may have chemical sensors or specialized teeth or digestive systems  Plant defenses include chemical toxins and protective structures

© 2014 Pearson Education, Inc. Differentiate between parasitism, mutualism, and commensalism.

© 2014 Pearson Education, Inc. Symbiosis  Symbiosis is a relationship where two or more species live in direct and intimate contact with one another

© 2014 Pearson Education, Inc. Parasitism  In parasitism (  /− interaction), one organism, the parasite, derives nourishment from another organism, its host, which is harmed in the process  Parasites that live within the body of their host are called endoparasites  Parasites that live on the external surface of a host are ectoparasites

© 2014 Pearson Education, Inc. Mutualism  Mutualistic symbiosis, or mutualism (  /  interaction), is an interspecific interaction that benefits both species  In some mutualisms, one species cannot survive without the other  In other mutualisms, both species can survive alone  Mutualisms sometimes involve coevolution of related adaptations in both species Video: Clownfish and Anemone

© 2014 Pearson Education, Inc. Commensalism  In commensalism (  /0 interaction), one species benefits and the other is neither harmed nor helped  Commensal interactions are hard to document in nature because any close association likely affects both species

© 2014 Pearson Education, Inc. Facilitation  Facilitation (  /  or 0/  ) is an interaction in which one species has positive effects on another species without direct and intimate contact  For example, the black rush makes the soil more hospitable for other plant species

© 2014 Pearson Education, Inc. Figure 41.9 (a) Salt marsh with Juncus (foreground) (b) With Juncus Without Juncus Number of plant species

© 2014 Pearson Education, Inc. Figure 41.UN03

© 2014 Pearson Education, Inc. Concept 41.2: Diversity and trophic structure characterize biological communities  Two fundamental features of community structure are species diversity and feeding relationships  Sometimes a few species in a community exert strong control on that community’s structure

© 2014 Pearson Education, Inc. Species Diversity  Species diversity of a community is the variety of organisms that make up the community  It has two components: species richness and relative abundance  Species richness is the number of different species in the community  Relative abundance is the proportion each species represents of all individuals in the community

© 2014 Pearson Education, Inc. Figure Community 2 B: 5% A: 80%C: 5% D: 10% Community 1 B: 25%A: 25% C: 25% D: 25% DCBA

© 2014 Pearson Education, Inc.  Two communities can have the same species richness but a different relative abundance  Diversity can be compared using a diversity index  Widely used is the Shannon diversity index (H) H  −(p A ln p A  p B ln p B  p C ln p C  …) where A, B, C... are the species, p is the relative abundance of each species, and ln is the natural logarithm

© 2014 Pearson Education, Inc.  Communities with higher diversity are  More productive and more stable in their productivity  Able to produce biomass (the total mass of all individuals in a population) more consistently than single species plots  Better able to withstand and recover from environmental stresses  More resistant to invasive species, organisms that become established outside their native range

© 2014 Pearson Education, Inc. How would biodiversity affect the topic levels in an ecosystem?

© 2014 Pearson Education, Inc. Trophic Structure  Trophic structure is the feeding relationships between organisms in a community  It is a key factor in community dynamics  Food chains link trophic levels from producers to top carnivores

© 2014 Pearson Education, Inc. Figure Quaternary consumers: carnivores Tertiary consumers: carnivores Secondary consumers: carnivores Primary consumers: herbivores and zooplankton Primary producers: plants and phytoplankton

© 2014 Pearson Education, Inc.  A food web is a branching food chain with complex trophic interactions  Species may play a role at more than one trophic level Video: Shark Eating a Seal

© 2014 Pearson Education, Inc. Figure Smaller toothed whales Sperm whales Baleen whales Crab- eater seals Elephant seals Leopard seals Birds Carnivorous plankton Humans Fishes Squids Krill Phyto- plankton Copepods

© 2014 Pearson Education, Inc. What are some leadership roles species can hold in a community?

© 2014 Pearson Education, Inc. Species with a Large Impact  Certain species have a very large impact on community structure  Such species are highly abundant or play a pivotal role in community dynamics

© 2014 Pearson Education, Inc.  Dominant species are those that are most abundant or have the highest biomass  One hypothesis suggests that dominant species are most competitive in exploiting resources  Another hypothesis is that they are most successful at avoiding predators and disease

© 2014 Pearson Education, Inc. Interpret this figure, for the sea star Pisaster. Results Year Number of species present ’64 Without Pisaster (experimental) With Pisaster (control) 5 ’66’65’67’69’68’70’72’71’73

© 2014 Pearson Education, Inc.  Keystone species exert strong control on a community by their ecological roles, or niches  In contrast to dominant species, they are not necessarily abundant in a community  Field studies of sea stars illustrate their role as a keystone species in intertidal communities

© 2014 Pearson Education, Inc.  Ecosystem engineers (or “foundation species”) cause physical changes in the environment that affect community structure  For example, beaver dams can transform landscapes on a very large scale

© 2014 Pearson Education, Inc. 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 mineral nutrients determines community structure, including the abundance of primary producers

© 2014 Pearson Education, Inc. Describe a model that would best show the biological control of organisms on each trophic level.

© 2014 Pearson Education, Inc.  The bottom-up model can be represented by the equation where N  mineral nutrients V  plants H  herbivores P  predators NVHPNVHP

© 2014 Pearson Education, Inc.  The top-down model, also called the trophic cascade model, proposes that control comes from the trophic level above  In this case, predators control herbivores, which in turn control primary producers NVHPNVHP

© 2014 Pearson Education, Inc. How are ecosystems repaired after disturbances?

© 2014 Pearson Education, Inc.  Biomanipulation is used to improve water quality in polluted lakes  In a Finnish lake, blooms of cyanobacteria (primary producers) occurred when zooplankton (primary consumers) were eaten by large populations of roach fish (secondary consumers)  Removal of roach fish and addition of pike perch (tertiary consumers) controlled roach populations, allowing zooplankton populations to increase and ending cyanobacterial blooms

© 2014 Pearson Education, Inc.  Decades ago, most ecologists favored the view that communities are in a state of equilibrium  This view was supported by F. E. Clements, who suggested that species in a climax community function as an integrated unit  Recent evidence of 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 it, and alters resource availability

© 2014 Pearson Education, Inc. Describe some disturbances that may affect the stability of an ecosystem.

© 2014 Pearson Education, Inc. Characterizing Disturbance  Fire is a significant disturbance in most terrestrial ecosystems  A high level of disturbance is the result of a high intensity and high frequency of disturbance  Low disturbance levels result from either low intensity or low frequency of disturbance

© 2014 Pearson Education, Inc.  The intermediate disturbance hypothesis suggests that moderate levels of disturbance can foster greater diversity than either high or low levels of disturbance  High levels of disturbance exclude many slow- growing species  Low levels of disturbance allow dominant species to exclude less competitive species

© 2014 Pearson Education, Inc. 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

© 2014 Pearson Education, Inc. Figure Alaska Glacier Bay Kilometers

© 2014 Pearson Education, Inc. Figure Pioneer stage Alaska Glacier Bay Kilometers

© 2014 Pearson Education, Inc. Figure Pioneer stage Dryas stage Alaska Glacier Bay Kilometers

© 2014 Pearson Education, Inc. Figure Alder stage Pioneer stage Dryas stage Alaska Glacier Bay Kilometers

© 2014 Pearson Education, Inc. Figure Spruce stage Alder stage Pioneer stage Dryas stage Alaska Glacier Bay Kilometers

© 2014 Pearson Education, Inc. Human Disturbance  Humans have the greatest impact on biological communities worldwide  Human disturbance to communities usually reduces species diversity  Trawling is a major human disturbance in marine ecosystems