© 2014 Pearson Education, Inc. Chapter 41 Overview: Communities in Motion  A biological community is populations of various species living close enough for interaction  For example, the “carrier crab” carries a sea urchin on its back for protection against predators

© 2014 Pearson Education, Inc. Concept 41.1: Interactions within a Community  Ecologists call relationships between species in a community interspecific interactions  Interspecific interactions can affect the survival and reproduction of each species. 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  Strong competition can lead to competitive exclusion, local elimination of a competing species. Two species competing for the same limiting resources cannot coexist in the same place

© 2014 Pearson Education, Inc. Ecological Niches and Natural Selection  Ecological niche, the specific set of biotic and abiotic resources used by an organism (it’s ecological role)  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. Predation  Predation (  /− interaction) refers to an interaction in which the predator kills and eats the prey  Some feeding adaptations of predators are claws, teeth, stingers, and poison  Behavioral defenses of the prey include hiding, fleeing, forming herds or schools, active self- defense, camouflage, toxins

© 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 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. Parasitism  In parasitism (  /− interaction) the parasite, derives nourishment its host, which is harmed  Some parasites change the behavior of the host in a way that increases the parasites’ fitness  Mind Control of rodents!! Symbiosis is a relationship where two or more species live in direct and intimate contact with one another. 3 General Types: Parasitism, Mutualism, Commensalism

© 2014 Pearson Education, Inc. Mutualism  Mutualistic symbiosis, or mutualism (  /  interaction), benefits both species  Mutualisms sometimes involve coevolution of related adaptations in both species (a) Ants (genus Pseudomyrmex) in acacia tree (b) Area cleared by ants around an acacia tree

© 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. Concept 41.2: Diversity and trophic structures  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  Species diversity depends on species richness and abundance 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.  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

© 2014 Pearson Education, Inc. Trophic Structures  Food chains link trophic levels from producers to top carnivores  A food web is a branching food chain with complex trophic interactions

© 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  Dominant species are those that are most abundant or have the highest biomass  Keystone species exert strong control on a community by their ecological roles, or niches  In contrast to dominant species, keystone species are not necessarily abundant in a community

© 2014 Pearson Education, Inc. In western N. America the uncommon sea star preys on mussels, which are the dominant species and strong competitor for space. Removing the sea star caused species richness to decline because the mussels monopolized the rock and eliminated most invertebrates and algae. Experiment 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. 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.  The bottom-up model can be represented by the equation NVHPNVHP where N  mineral nutrients V  plants H  herbivores P  predators

© 2014 Pearson Education, Inc.  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  Scientist have used this approach to control algae blooms by removing fish so there is more zooplankton to eat the algae NVHPNVHP

© 2014 Pearson Education, Inc. Concept 41.3: Disturbance influences species diversity and 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 disturbances  Describe some disturbances.

© 2014 Pearson Education, Inc.  The large-scale fire in Yellowstone National Park in 1988 demonstrated that communities can often respond very rapidly to a massive disturbance  The Yellowstone forest is an example of a nonequilibrium community (a) Soon after fire (b) One year after fire

© 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  Early arrivals may facilitate the appearance of later species by making the environment favorable  Early species may inhibit the establishment of later species

© 2014 Pearson Education, Inc.  Retreating glaciers provide a valuable field research opportunity for observing succession  Succession in Glacier Bay, Alaska, follows a predictable pattern of change in vegetation and soil characteristics 1.The exposed area is colonized by pioneering plants, including liverworts, mosses, fireweed, Dryas, and willows 2.After about three decades, Dryas dominates the plant community 3.A few decades later, alder invades and forms dense thicket. 4. In the next two centuries, alder are overgrown by Sitka spruce, western hemlock, and mountain hemlock

© 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

© 2014 Pearson Education, Inc. Figure 41.23