1 Community Ecology Chapter 56

2 Biological Communities Community: all the organisms that live together in a specific place –Evolve together –Forage together –Compete –Cooperate

3 Interactions in a community –Predation –Mutualism Biological Communities

4 Most ecologists favor the individualistic concept In communities, species respond independently to changing environmental conditions Community composition changes gradually across landscapes

5 Ecological Niche Niche: the total of all the ways an organism uses the resources of its environment –Space utilization –Food consumption –Temperature range –Appropriate conditions for mating –Requirements for moisture and more Billock

6 Ecological Niche Other causes of niche restriction –Predator absence or presence Plant species –Absence of pollinators –Presence of herbivores Billock

Ocean Chthamalus Balanus EXPERIMENT High tide Low tide Chthamalus realized niche Balanus realized niche Realized niche: actual set of environmental conditions, presence or absence of other species, in which the species can establish a stable population

8 Ecological Niche Fundamental niche: the entire niche that a species is capable of using, based on physiological tolerance limits and resource needs EXPERIMENT

9 Ecological Niche Interspecific competition: 2 species attempt to use the same resource and there is not enough resource for both Competitive exclusion: Strong competition can lead to competitive exclusion, local elimination of a competing species The competitive exclusion principle states that 2 species competing for the same limiting resources cannot coexist in the same place

10 G.F. Gause’s experiment on competitive exclusion using three Paramecium species shows this principle in action Principle of competitive exclusion

Competitive exclusion redefined: no two species can occupy the same niche indefinitely when resources are limiting-found in two of his Paramecium species Niche overlap and coexistence Species may divide up the resources, this is called resource partitioning

12 Ecological Niche Niche overlap and coexistence Competitive exclusion redefined: no two species can occupy the same niche indefinitely when resources are limiting Species may divide up the resources, this is called resource partitioning Gause found this occurring with two of his Paramecium species

13 Resource partitioning - seen in similar species that occupy same geographic area result from the process of natural selection Resource partitioning among sympatric lizard species

14 Predator-Prey Predation: consuming of one organism by another Predation strongly influences prey populations Prey populations can have explosions and crashes –White-tail deer in Eastern US –New Zealand: Stephen Island wren extinct because of a single cat introduction of rats, dogs, cats on islands –

15 Predator-Prey Predation and coevolution –strong selective pressure on the prey population –Features that decrease the probability of capture are favored –Predator populations counteradapt to continue eating the prey –Coevolution race may ensue

16 Predator-Prey Plants adapt to predation –Chemical: secondary compounds Oils, chemicals, poison milky sap and others –Herbivores coevolve to continue eating the plants

17 Chemical defenses in animals - Monarch butterfly –caterpillars feed on milkweed and dogbane plants –incorporate chemicals from the plants for protection from predation –Butterflies are eaten by birds, but the Monarch contains the chemical from the milkweed that make the birds sick- learns not to eat butterflies

Predator-Prey –Insects and other animals that are poisonous use warning coloration –Organisms that lack specific chemical defenses are seldom brightly colored –Poison-dart frogs produce toxic alkaloids in the mucus that covers their brightly colored skin Chemical defenses Defensive coloration

19 Predator-Prey Defensive coloration –Camouflage or Aposematic (cryptic) coloration help nonpoisonous animals –Camouflaged animals blend with their surroundings; do not usually live together in groups Animals closely resemble surroundings

20 Predator-Prey Mimicry allows one species to capitalize on defensive strategies of another Hawkmoth larva puffs up to look like poisonous snake

21 Predator-Prey Batesian mimicry –Palatable insects that resembled brightly colored, distasteful species –Mimics would be avoided by predators because they looked like distasteful species

22 Predator-Prey Hawkmoth larva puffs up to look like poisonous snake hawkmoth larvae green parrot snake Müllerian mimicry –Several unrelated but poisonous species come to resemble one another –Predator learns quickly to avoid them –Some predators evolve an innate avoidance Both mimic types must look and act like the dangerous model

Predator-Prey What kind of mimicry? Coral snake is poisonous King snake is not Red on yellow, poison fellow; red on black, safe from attack

24 Species Interactions Symbiosis: two or more kinds of organisms interact in more-or-less permanent relationships All symbiotic relationships carry the potential for coevolution Three major types –Commensalism, Mutualism, Parasitism

25 Species Interactions Commensalism benefits one species and is neutral to the other –Spanish moss: an epiphyte hangs from trees

26 Commensalism? Oxpickers and grazing animals –Oxpickers eat parasites off of grazers –Sometimes pick scabs and drink blood –Grazers could be unharmed by the insects the oxpickers eat

27 Species Interactions Mutualism benefits both species Coevolution: flowering plants and insects Ants and acacias –Acacias provide hollow thorns and food –Ants provide protection from herbivores

28 Species Interactions Parasitism benefits one species at the expense of another External parasites: feed on exterior/interior surface of an organism flatworm that lives in ants changes the behavior of the ant to climb to the top of a blade of grass to be eaten

29 Species Interactions Ecological processes have interactive effects –Superior competitors may be reduced in number by predation This allows other species to survive when they could have been out competed Starfish eat barnacles, allowing other species to thrive instead of being crowded out by the explosive population of barnacles

30 Indirect effects: presence of one species may affect a second by way of interactions with a third species

31 Keystone species: species whose effects on the composition of communities are greater than one might expect based on their abundance Sea otter is a keystone predator in North Pacific What is the impact of the Orca whale?

32 Keystone Species Beavers construct dams and transform flowing streams into ponds, creating new habitats for many plants and animals

33 Succession and Disturbance Succession happens because species alter the habitat and the resources available in ways that favor other species entering the habitat Primary succession: occurs on bare, lifeless substrate; organisms gradually move into an area and change its nature Secondary succession: occurs in areas where an existing community has been disturbed but organisms still remain

34 Succession and Disturbance Primary succession on glacial moraines

35 Succession and Disturbance Three dynamic concepts in the process –Tolerance: early species are characterized by r-selected species tolerant of harsh conditions –Facilitation: early species introduce local changes in the habitat. K-selected species replace r-selected species –Inhibition: changes in the habitat caused by one species inhibits the growth of the original species

36 Succession and Disturbance Succession after a volcanic eruption