Download 15 Competition 2010

LECTURE 14
CH 16
COMPETITION
Before lecture on Tuesday…
1. Take the quiz on www.myfootprint.org.
2. Insert your result in the lecture outline, as shown below and bring lecture outline.
3. Make notes as to which category you exceed average (e.g. food, transportation)
Learn the concepts in bold below; LOTS of vocabulary may be new!
MAJOR CONCEPTS
1) Facilitation is the alternative to competition; it is understudied.
2) Consumers compete by using a resource that reduces availability to others.
3) Competition occurs through exploitation of shared resources or direct interference.
4) Responses of plant and animal species to intraspecific competition include decrease in
growth, delay in reproduction, and decrease in reproduction and survival.
5) The theory of competition and coexistence is an extension of logistic growth models.
6) The niche reflects the environmental requirements of species; its dimensions shrink
when faced with interspecific competition.
7) Organisms evolve in response to competition and may not be competing today; many
types of evidence are used to deduce that (past) competition explains current traits.
8) The principle of competitive exclusion arose when species failed to coexist in the lab.
9) Habitat productivity can influence plant competition.
10) Consumers of competitors can influence the outcome of competition.
11) Experimental field studies demonstrate widespread competition in nature.
PART 1
I. Facilitation as alternative to competition 296-7
Sp 1 aids recruitment or survival of sp 2 14.10
Not altruism; no cost to facilitator
Understudied relative to competition
II Competition: Use/defense of limiting resource that reduces availability to others 329-30
Resource: any substance or factor that is:
a) consumed by an organism
b) supports increased population growth rates as its availability increases.
Superior competitors can persist at lower resource levels. 16.2
III Types of competition 338-339
Exploitation (scramble; indirect): use by 1 makes unavailable to another
Vs. Interference (direct): active defense by 1 makes unavailable to another
Intraspecific (within species) vs. interspecific (between species)
Expect intrasp > intersp because individuals more similar 331; 16.4
IV Allelopathy 339-40
Chemical interference competition by plants 16.14, 16.15, 16.16
Chemical exudates directly inhibit growth of competitor
Circumstantial and laboratory evidence
Difficulty of demonstrating experimentally in field
Alternative explanations of patterns (e.g. seed predation)
V Types of resources (a condition, e.g. temperature, is NOT a resource) 330
Plants
Abiotic (light, water, nutrients)
Biotic (microbial symbionts such as N-fixing bacteria, pollinators, seed dispersers)
Animals
Abiotic (space, territory, hiding places) 16.3
Biotic (food)
Renewable (constantly regenerated) 332
Non-renewable (occur in fixed amounts and can be fully re-used)
VI Liebig’s Law of Minimum 332
Population limited by the most scarce single resource
Assumes no interaction between resources in determining response
Can be violated because of interaction and synergism between resources 16.5, 16.6
Law of constant yield: if exceed K in planting density, no increase in population size
above K
VII Negative consequences of competition for population growth:
Intraspecific competition in plants  density-dependence of population growth 243-44
Decreases growth and size hierarchies develop 11.23
Decreases reproduction (births) +
Increases mortality (deaths) (‘self-thinning’ of population)  lowers r 11.24,11.25
Intraspecific competition in animals  density-dependence of population growth 239-42
Decreases growth of individual
Increases age of sexual maturity (delays births)
Decreases births + increases mortality lowers r 11.19,11.20
VIII Logistic equation extended to include theory of competition and coexistence 334-35
Based on intraspecific competition decreasing per capita pop. growth rate
via density-dependent birth and death rates; causes r to decrease 16.8
Population size continues to increase until N = K, but
rate of pop growth slows as N approaches K (as (K-N)/K approaches 0)
at K, r = 0 16,8
Modifications to logistic growth equations by adding interspecific competition
Modified to include interspecific competition; 16.9
add effects of sp 1 on 2; sp 2 on 1
Competition coefficients: conversion factor to convert sp 2 individuals into
equivalent # of sp 1
Presence of sp 2 decreases size of K available to sp 1
 = effect of sp2 on sp 1 N1 =  N2 = saturating effect
 = effect of sp1 on sp2
N2 =  N1 = saturating effect
 +  = proportionality constants of effect of 1 sp on 2nd sp
dN1/dt = r1N1 (K1 - N1 -  N2) / K1
dN2dt = r2N2 (K2 – N2 -  N1) / K2
PART 2
I Niche pg. 423-4
Ranges of conditions and resource qualities within which species persists
Niche axis
Niche breadth
Multiple niche axes  hypervolume
In practice, study 1 or 2 axes
Intraspecific competition  selects for broader niche
Interspecific competition  may select for narrower niche (leads to specialization)
II Interspecific competition
Invasion by new species brings overlap  reduced niche breadth  allows more
species packed into community
Fundamental niche (without competitors) Vs. Realized niche (with competitors) 200
‘Ghost of competition past’: today’s organisms no longer in competition because of
past selection to avoid competition
Often lose evidence of competitive exclusion because poor competitor is gone
III Types of evidence used to deduce that (past) competition explains current traits
A. Niche separation (resource partitioning); reduced niche overlap
B. Habitat shift: weaker competitor changes habitat or expands habitat when other
species absent
C. Character displacement 359 17.16, 17.17
D. Competitive exclusion: two species can’t coexist on same limiting resource 16.7
Classic experiments of interspecific competition
Winner of competition can depend on environmental conditions
Two species can coexist if limited by different resources 16.10
E. Competitive release when one competitor is gone  other species expands
IV Predation can influence outcome of competition 340-42
Predators can maintain prey species diversity by reducing superior competitors 16.17, 16.18
Apparent competition: Herbivores or predators can determine the competitive balance 16.19,
16.20
V Field studies: how demonstrate competition? 328-29
Introduce (add) species it excludes related species
Removal of species  competitive release (increase in remaining competitors)
Compare intra-vs. interspecific competition in field 16.1
Both can occur simultaneously
Evidence of asymmetric competition 336-37 16.11
Sp 1 controls Sp 2 in Sp 2’s habitat, but not vice versa
Occurs when different factors limit the populations of competitors
Possibility of tradeoffs: superior competitive ability in favorable habitat may be linked
to poor tolerance of stressful conditions; and vice versa
Summary 1-16!