1. CHAPTER 57 SPECIES INTERACTIONS Brenda Leady, University of Toledo
Prepared by
Brenda Leady, University of Toledo
Copyright (c) The McGraw-Hill Companies, Inc. Permission required for reproduction or display.

4. Competition Intraspecific – between individuals of the same species
Interspecific – between individuals of different species
Resource competition – organisms compete indirectly through the consumption of a limited resource
Interference competition – individuals interact directly with one another by physical force or intimidation

6. Amensalism – one species has a strong effect on another, but the reverse effect is negligible
-/0 relationship
Allelopathy
Roots excreting chemicals to kill off competitors
Penicillin inhibiting the growth of bacteria

7. Connell’s Experiments with Barnacle Species Show That One Species Can Competitively Exclude Another in a Natural Setting
1954, Joseph Connel worked with 2 barnacles along the Scottish coastline
Determine range of Chthamalus stellatus in the absence of competition from Semibalanus balanoides (formerly known as Balanus balanoides)
Potential distribution (the fundamental niche) of Chthamalus extends over the entire intertidal zone, its actual distribution (the realized niche) is restricted to the upper zone
Among the first to show that, in a natural environment, one species can actually outcompete another, affecting its distribution within a habitat

9. Outcomes of competition can vary
Late 1940s, Thomas Park examined competition between two flour beetles, Tribolium confusum and Tribolium castaneum
Presence of parasite (biotic factor) can alter the outcome of competition
Random variation, stochasticity, evident
Also influenced by temperature and moisture
Mechanism of competition is predation of larva by other species

11. Field studies
1983 review competition found in 55% of 215 species surveyed, demonstrating that it is indeed frequent in nature
Generally in studies of single pairs of species utilizing the same resource, competition is almost always reported (90%)
Percent competition varies with the number of species involved
Plants showed a high degree of competition
Marine organisms tended to compete more than terrestrial ones

13. Competitive exclusion hypothesis
Gause worked with 3 protists – Paramecium aurelia, Paramecium bursaria, and Paramecium caudatum
Grown separately all 3 grew logistically
When P. caudatum and P. aurelia grown together, P. caudatum went extinct
When P. caudatum and P. bursaria grown together, neither went extinct
Concluded that 2 species with exactly the same requirements cannot live together in the same place and use the same resources, that is, occupy the same niche
Competitive exclusion hypothesis – complete competitors cannot coexist

15. Robert MacArthur examined coexistence between five species of warblers feeding within spruce trees in New England
Found that the species occupied different heights and portions in the tree and thus each probably fed on a different range of insects
Resource partitioning – differentiation of niches, both in space and time, that enables similar species to coexist in a community

17. Morphological differences allow coexistence
Some partial level of competition between complete competitors can exist if it is not severe enough to drive one competitor extinct
G. Evelyn Hutchinson compared size differences in feeding apparatus between sympatric (same geographic area) and allopatric (different geographic areas) species
When species were sympatric, feeding apparatus size changed to specialize on different food
Size differences did not occur in allopatric species
Character displacement – tendency for 2 species to diverge in morphology and resource use due to competition
Galapagos finch example

19. Predation
Categories of predation can be classified according to how lethal they are for the prey and how close is the association between predator and prey

20. Antipredator strategies
Chemical defense
Bombardier beetle ejects hot spray
Aposematic coloration, or warning coloration, which advertises an organism’s unpalatable taste
Many tropical frogs have bright coloration to advertise their skin’s lethality
Cryptic coloration
Camouflage
Stick insects mimic branches
Sea horses adopt body coloration to mimic habitat

22. Displays of intimidation
Mimicry
Resemblance of mimic to another organism (model)
Mullerian mimicry – noxious species converge to reinforce warning, black and yellow stripes of bees and wasps
Batesian mimicry – palatable mimic resembles unpalatable model, scarlet king snake and coral snake
Displays of intimidation
Porcupine fish inflates itself
Deceive predator about ease of eating prey
Fighting
Horns and antlers can be used in defense

24. Escape
Grasshoppers powerful jumping ability
Armor
Shells of turtles provide strong defense
Beetle exoskeleton
Masting
Synchronous production of progeny satiate predators and allow some young to survive
Seed herbivory
Periodical cicadas
Most common antipredator mechanisms in arthropods were chemical defenses and aposematic coloration

25. Predators still affect prey densities
Importance of predation depends on if it is
Donor-controlled system, prey supply is determined by factors other than predation, such as food supply, so that removal of predators has no effect on prey density
Predator-controlled system, action of predator feeding reduces supply of prey, so removal of predator results in increase in prey

27. Invasive species do not have their natural predators
Brown tree snake introduced to Guam
By 1980’s 8 of 11 of island’s forest birds extinct
Birds had no defense against snake they didn’t evolve with
Systematic decline in whales of various species in response to human whaling industry

30. Plant/herbivore arms race
Herbivory can be lethal to small species
Usually not lethal to larger species
Generalist herbivores can feed on many plant species
Specialist herbivores restricted to 1 or 2 host plants
2 proposals explain why every plant isn’t consumed
Predators and parasites keep herbivore numbers low
Plant defenses make a difference

31. Plant defenses Array of unusual and powerful chemicals
2 classes – nitrogen containing (alkaloids) and lacing nitrogen (phenolics and terpenoids)
Secondary metabolites – not part of primary energy generating metabolic pathway
Over 25,00 compounds
Also mechanical defenses like thorns and spines

33. Herbivores can overcome plant defenses
Detoxify using 2 pathways
Oxidation – catalysis of secondary metabolite to corresponding alcohol by mixed-function oxidases (MFOs)
Conjugation – unites results of oxidation with another molecule to create inactive and readily excreted product
Certain chemicals that are toxic to generalist herbivores actually increase the growth rates of adapted specialist species

34. Parasitism
One organism feeds off another, but does not normally kill it outright
Predatory organism is termed a parasite and the prey a host

35. Parasitic flowering plants
Holoparasites lack chlorophyll and are totally dependent on the host plant for their water and nutrients
Rafflesia arnoldii, which lives most of its life within the body of its host with only the flower developing externally (largest known flower in the world)
Hemiparasites generally do photosynthesize, but they lack a root system to draw water and thus depend on their hosts for that function
Mistletoe (Viscum album)

37. Host range
Monophagous – feed on one or two closely related hosts
Polyphagous – feed on many hosts
Size
Microparasites – multiply within hosts, usually within cells (bacteria and viruses)
Macroparasites – live in host but release juvenile stages outside host’s body
Site
Ectoparasites – live on the outside of the host body (fleas and ticks)
Endoparasites – live inside the host body (bacteria and tapeworms)

38. Parasites may outnumber free-living species by four to one
Most plant and animal species harbor many parasites
Few cases of experimental removal of parasites confirm that parasites can reduce host population densities
Blue tit and parasitic blowfly larvae example

40. Introduced parasite species an opportunity to examine parasitism as a mortality factor
Plants
Chestnut blight virtually eliminated chestnut trees in North America
Dutch elm disease eliminated elms in Europe and North America
Canker eliminated cypress in Italy
Animals
Canine distemper caused a large decline in the last remaining black-footed ferrets in the US
1/3 of lions wiped out by canine distemper in Serengeti National Park
Ethiopian wolf has been vaccinated against rabies
Mountain gorillas vaccinated against measles

42. The Fight Against Plant Diseases
Sudden oak death is a recently recognized disease killing tens of thousands of oak trees and other plants in California
Usually a forest disease but known to infect woody ornamentals like rhododendrons
Mapped genome of disease-carrying fungus to help develop specific tests for disease
Some have suggested limited, cautious transfer of resistant genes to threatened species
Using traditional breeding technologies to cross susceptible plant with resistant species can later affect appearance of original plant

43. Mutualism
Close associations are known between species in which both species benefit
Leaf-cutting ants and fungus
Ants chew up leaves to feed to fungus they care for
Fungus produces gongylidia as ant food
Ants circumvent chemical defenses of leaves

44. Defensive mutualism Dispersive mutualism
Animal defends a plant or herbivore
Ants protect aphid and aphid secretes honeydew
Facultative mutualism since they can live apart
Ants nesting in acacia trees defend the tree and trim away competing plants
Obligatory mutualism since neither can live without the other
Dispersive mutualism
Involve pollination and seed dispersal
Plant would like pollinator with high fidelity to one species that moves quickly among individuals
Animal wants to be a generalist to obtain as much food from many flowers in a small area to reduce energy expenditure
Although mutualisms are beneficial, optimal needs of each party can be different

46. Commensalism
One member derives a benefit while the other neither benefits nor is harmed
Epiphytes growing in trees do not harm the trees
Cattle egrets benefit from cattle stirring up insects
Phoresy – one organism uses another for transportation
Flower-inhabiting mites use hummingbird nostrils
Cheating
Grass-pink orchid produces no nectar, but it mimics the nectar-producing rose pogonia and is therefore still visited by bees
Plants cheat seed-dispersal agent out of meal with barbs or hooks on seeds

48. Conceptual models
Bottom-up model – food limitation controls population density
Plants regulate the population size of all other species that rely on them as the source of energy
Nitrogen-limitation hypothesis – increasing supply of nitrogen to plants will increase herbivore population size, survivorship, growth and fecundity
Top-down model – natural enemies control population densities
Predators control prey populations
Herbivores control plant populations
Evidence from studies where natural enemies are introduced to control exotic pest species
Small cactus moth brought in to control prickly pear cactus growth in Australia

50. Modern models suggest both important
Recently, different models have been proposed that take into account the effects of both natural enemies and limited resources on species
Ecosystem exploitation hypothesis – strength of mortality factors varies with availability of plant biomass involved
Simple systems with limited plants resource limited
At the other end, when plants are abundant, they support herbivores and carnivores, which compete