LECTURE PRESENTATIONS For CAMPBELL BIOLOGY, NINTH EDITION Jane B. Reece, Lisa A. Urry, Michael L. Cain, Steven A. Wasserman, Peter V. Minorsky, Robert B. Jackson Chapter 54 Community Ecology 2011 Pearson Education, Inc. Lectures by Erin Barley Kathleen Fitzpatrick 1
Overview: What Is a Community? A biological community is an assemblage of populations of various species living close enough for potential interaction Relationships between species in a community are called interspecific interactions Interspecific interactions affect species survival and reproduction Examples are competition, predation, herbivory, and symbiosis (parasitism, mutualism, and commensalism) 2
3
4
Competition Interspecific competition Two different species compete for the same limited resource Squirrels and black bears compete for acorns 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 5
Ecological Niches Ecological niche Sum of an organism s use of biotic and abiotic resources An ecological niche can also be thought of as an organism s ecological role Interspecific competition occurs when the niches of two populations overlap Ecologically similar species can coexist in a community if there are one or more significant differences in their niches As a result of competition, a species fundamental niche may differ from its realized niche 6
Chthamalus Balanus High tide Chthamalus realized niche High tide Ocean Balanus realized niche Low tide Ocean Chthamalus fundamental niche Low tide 7
A. insolitus usually perches on shady branches. A. ricordii A. distichus perches on fence posts and other sunny surfaces. A. aliniger A. distichus A. insolitus A. christophei A. cybotes A. etheridgei Resource partitioning is differentiation of ecological niches, enabling similar species to 8 coexist in a community
Predation Predation refers to interaction where one species, the predator, kills and eats the other, the prey Some feeding adaptations of predators are claws, teeth, fangs, stingers, and poison Prey display various defensive adaptations Behavioral defenses include hiding, fleeing, selfdefense, and alarm calls Animals also have morphological and physiological defense adaptations 9
Chemical defenses (aposematic warning): the poison-arrow frog 10
Mimicry: harmless frog is very similar to poisonous frogs Top: the harmless mimic, Allobates zaparo. Middle: Epipedobates bilinguis, the toxic poison dart frog that A. zaparo mimics. Bottom: E. parvalus, the more abundant, more toxic poison dart frog. Photo: David Cannatella. 11
Fig. 54-5 (a) Cryptic coloration Canyon tree frog (b) Aposematic coloration Poison dart frog Cryptic coloration, or camouflage, makes prey difficult to spot Animals with effective chemical defense often exhibit bright warning coloration, called aposematic coloration (c) Batesian mimicry: A harmless species mimics a harmful one. Hawkmoth larva (d) Green parrot snake Cuckoo bee Yellow jacket 12 Müllerian mimicry: Two unpalatabl species mimic each other.
Remarkable resemblances. A leaf, a bird dropping Owl butterfly (above) and long-eared owl (right) 13
Fig. 54-6 Herbivory refers to an interaction in which an herbivore eats parts of a plant or alga A West Indies manatee (Trichechus manatus) in Florida 14
Parasitism In parasitism, one organism, the parasite, derives nourishment from another organism, its host, which is harmed in the process 15
Parasitism: The relation between two different kinds of organisms when one organism [the parasite] benefits, and the other [the host] is adversely affected [weakened, sickened, damaged etc]. An extreme example of blowfly parasitism on a 6- day-old nestling Purple Martin In the photo, a tomato hornworm is covered with cocoons of pupating braconid wasps. 16
Disease Effects of disease on populations and communities are similar to those of parasites Pathogens, disease-causing agents, are typically bacteria, viruses, or protists 17
Figure 54.7 Mutualistic symbiosis, or mutualism, is an interspecific interaction that benefits both species (a) Acacia tree and ants (genus Pseudomyrmex) Mutualism between acacia trees and ants 18 (b) Area cleared by ants at the base of an acacia tree
Mutualism 19
Mutualism The birds called Oxpeckers are there for the food. Oxpeckers pick blood-sucking ticks and other parasites off the rhinos The relationship between the oxpecker and the rhinoceros is an example of "mutualism", a relationship in which both organisms benefit. 20
Commensalism: the relation between two different kinds of organisms when one receives benefits Commensalism: from the other without damaging it Clown fish with sea anemone Mussel shell with barnacles 21
Commensalism In commensalism, one species benefits and the other is apparently unaffected 22
Dominant and keystone species exert strong controls on community structure In general, a few species in a community exert strong control on that community s structure Two fundamental features of community structure are species diversity and feeding relationships 23
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 total number of different species in the community Relative abundance is the proportion each species represents of the total individuals in the community 24
Two 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 are rare 25
Species composition of woodlot A 26
Species composition of woodlot B 27
28
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 29
Quaternary consumers Carnivore Carnivore Tertiary consumers Carnivore Carnivore Carnivore Secondary consumers Carnivore Herbivore Primary consumers Zooplankton Primary producers Plant A terrestrial food chain Phytoplankton A marine food chain 30
Quaternary, tertiary, and secondary consumers Tertiary and secondary consumers Secondary and primary consumers Primary consumers A food web Producers (plants) 31
Food Webs Baleen whales Crab-eater seals Humans Smaller toothed whales Leopard seals Birds Fishes Squids Elephant seals Sperm whales A food web is a branching food chain with complex trophic interactions Carnivorous plankton Euphausids (krill) Copepods Phytoplankton 32
Tertiary consumers Secondary consumers 10 kcal 100 kcal An idealized pyramid of production Primary consumers 1,000 kcal Producers 10,000 kcal 1,000,000 kcal of sunlight 33
Food energy available to the human population at different trophic levels Trophic level Secondary consumers Human meat-eaters Primary consumers Human vegetarians Cattle Producers Corn Corn 34
Dominant Species 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 One hypothesis suggests that dominant species are most competitive in exploiting resources Another hypothesis is that they are most successful at avoiding predators 35
Keystone Species In contrast to dominant species, keystone species are not necessarily abundant in a community They exert strong control on a community by their ecological roles, or niches 36
Number of species present Field studies of sea stars exhibit their role as a keystone species in intertidal communities 20 15 10 5 With Pisaster (control) Without Pisaster (experimental) 0 1963 64 65 66 67 68 69 70 71 72 73 37
Number per Grams per Otter number (% max. count) 100 Food chain before killer whale involvement in chain 80 60 40 20 0 Sea otter abundance 400 300 200 100 0 Sea urchin biomass 0.25 m 2 10 8 6 4 2 0 1972 1985 1989 Year Total kelp density 0.25 m 2 1993 1997 Food chain after killer whales started preying on otters Observation of sea otter populations and their predation shows how otters affect ocean communities 38
Keystone Arch collapse with removal of keystone Keystone absent 39
Ecosystem Engineers (Foundation Species) Some organisms exert influence by causing physical changes in the environment that affect community structure For example, beaver dams can transform landscapes on a very large scale 40
Number of plant species Some foundation species act as facilitators that have positive effects on survival and reproduction of some other species in the community 8 6 4 2 Salt marsh with Juncus (foreground) 0 With Juncus Conditions Without Juncus 41
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, presence or absence of mineral nutrients determines community structure, including abundance of primary producers 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 42
Pollution can affect community structure and dynamics Biomanipulation can help restore polluted communities 43
Figure 54.UN03 44
45
Thank you for your attention and participation! 46