Biology 106 Lecture Topic # 23 Population Regulation via Species Interactions
Types of Species Interactions - influence a populations growth (via who survives and reproduces)
+ = positive, - = negative, 0 = no effect
# 1. Competition -/-
*occurs within a community * both popln's limited by interaction
* compete for limiting resource * often one spp wins & the other loses
Plants often compete for:
Animals commonly compete for:
Two Major Types of Competition
1. Interspecific = between 2 kinds of organisms
*greatest between similar organisms, such as those that obtain food in a similar fashion i.e., same trophic or feeding level; herb. vs. herb. or carn. vs. carn.
2. Intraspecific = between populations of the same kind of organisms
The Principle of Competitive Exclusion = if 2 spp are competing for the same limited resource, one will be more efficient at utilizing or controlling access to the resource, resulting in the eventual elimination of the other spp.
In the paramecium ex. the fastest growing spp (l r) performed the best under competitive conditions
BUT not always: ex. 2 spp of duckweed Lemna gibba (low r) vs.Lemna polyrrhiza (high r)
L. g. always replaces L. p. !!!!
The winner may change depending upon changing environmental conditions
ex. Tribolium (flour beetles) T. castaneum vs. T. confusum
ex. white vs. strawberry clover *grown under varying densities
Examples of Competition in Nature:
1. Warblers studied by Robert MacArthur
*5 spp of warblers *initially thought competing for same resource
*Each spp forages in a different part of the tree and eats a different subset of insects
*Spp NOT TRULY COMPETING!!! *A NICHE SHIFT is probably responsible
2. Ten Species of Darwin's Finches
*Classic ex. of Character Displacement via adaptive radiation that decreased competition between spp. by changes in bill size, shape, and structure *Also called a NICHE SHIFT
Niche Concept Niche = is an organisms profession, distinct from its habitat alone, = address
incl: abiotic and biotic interactions, Niche IS NOT synonymous with habitat
Two Types of Niches
1. Realized or Ecological Niche = actual role an organism plays in a particular ecosystem
2. Fundamental Niche = theoretical, the role an organism would play in the absence of competitors
Niche w/r to Gause's Competitive Exclusion Hypothesis
-no two spp can occupy same niche indefinitely, -coexist while competing for same resource
-one or more features of niche will always differ, thus decreasing competition
-role of competitive exclusion is more obvious when resources are drastically reduced
-ALL factors that define an organism's niche are difficult to determine
#2. Predator - Prey Interactions + / -
*limits sizes of poplns in a cyclic fashion
*every organism within a community is part of a food web
*ex. of simple food web; herbivore = carnivore = omnivore = primary producer = primary consumer = secondary consumer =
Cyclic nature of predator-prey interactions, ex.'s,
1. prey poplns driven to low but recoverable #'s 2. pred #'s subsequently decrease
3. prey #'s increase 4. pred #'s increase
Predation and Species Diversity-many studies have demonstrated that predator spp are an important factor in maintaining spp diversity ex.
#3. Plant - Herbivore Interactions
*transfer of energy from primary producer to primary consumer
*plants fix 1% of available solar energy & herbivores incorporate 10% of this energy into tissues
*we only manufacture 8/20 essential amino acids & we are dependent on plants for other 12!
1. Plant Defenses against Herbivory, ex.
a. Morphological Defenses -
b. Chemical Defenses
1. restrict a.a. composition
2. prod. of secondary compounds;
c. Coevolved plant-herbivore interactions - *are likely to be slower to respond if each spp is engaged in multiple predator-prey interactions, ex. Heliconious butterflies & Passion vines.
2. Chemical Defenses in Animals: Produce own, Manuf. based on plants or other animals secondary cmpds, Store rather than breakdown 2o cmpd.
These relationships are important w/r to biological control
1. near eradication of prey may cause extinction of predator
2. prey must survive in small #'s for pred. to survive
ex. rabbits introduced to Australia and New Zealand as an alternative food source and viral disease myxomatosis
Mechanisms to Escape Predation by Prey: 1. camouflage or cryptic coloration, 2. physical hiding place,s 3. temporal strategies
Plant - Herbivore Interactions
REMAINING INFO IN AN EARLIER LECTURE IN BIOL 106
4. Advertise distastefulness - Aposematic or warning coloration
a. Nonpoisonous animals?
b. Mimicry = visual appearance and behavior imitated.
1. Batesian = related, but unprotected spp resembles protected spp
2. Muellerian = unrelated, but protected spp resemble one another. Group defense enhanced via larger #'s ex. yellow and black coloration of flies, wasps, and bees
SYMBIOSIS = Close association of 2 or more dissimilar organisms; ex.s
#3. Parasitism + / -
* A special form of predation, close association, nec. for predator
* Predator much smaller than prey
* Internal association more specialized than external association
ex. intestinal worms, lice, parasitic plants
#4. Commensalism + / o * Interaction is necessary for benefitting organism
*One spp physically attached to other spp that exhibits no ill effects
ex. remora fish and shark ex. epiphytes
But any benefit?? There is a gray zone between commensalism and mutualism
5. Mutualisms + / + * A necessary association for both spp
ex. mycorrhizae fungi and plant roots
ex. flowering plants and pollinators
A. Coevolved Mutualisms
ex. ants and acacia trees in tropics
ex. yucca moth and yucca plant in S. W. USA
THIS MATERIAL OMITTES FROM 106, SPR 97 AND SPR 99
I. Coevolution - term coined in 1964 by Paul Ehrlich and PeterRaven
A. Coevolution Specifically defined = requires that each of 2 or more species change in genetic composition in response to a genetic change in the other or each species must evolve specifically and reciprocally respond to each other.
* most easily thought of as a single pair of species
However, most species interact with a variety of other species, therefore
B. Diffuse Coevolution - defined by Henry Howe in 1984
*Where a trait will evolve in response to a class of species and their general behavior than to any specific species particular behavior or reciprocal evolutionary interactions among classes of species