Unit II: Population Ecology

1
Unit II Population Ecology

• A. Single-species population growth
• B. Predator-prey interactions (Trophic levels)
• C. Interspecific competition
• D. Mutualism (positive interactions)

2
Outline to trophic level lectures Ch. 14
0. Introduction to population interactions (2
species) I. Introduction to 2-trophic level inte
ractions (exploitation) A. Background premises a
nd terms B. Patterns in nature ?Hypotheses II.
Simple models (Ch. 14 and Ch. 6 pp. 146-8)
A. Form of model B. Functional Responses C. Be
havior of model III. Realistic refinements of mo
del A. Prey K 1. Paradox of enrichment 2. Pr
edator regulation of prey and predator efficiency
B. Time lags predator-prey instrinsic time scal
es
3
Acquiring resources

• In lecture 6, we considered one species in
  isolation, in a biotic vacuum what causes
  births and deaths to occur?
  
• In other words, how do we account for acquiring
  resources at the population level? We already
  considered this question at the individual level,
  with photosynthesis, foraging, and
  territoriality.
• When individuals acquire resources, they interact
  with each other (same population/species) and
  
• with individuals in other populations/of other
  species the next series of lectures
  
• Individuals in the interaction
• Either gain or lose
• (fitness is increased or decreased)

4
Effect of interaction on species 1
_
0

_
Amensalism ??? Does this Evolve
ExploitationTrophic interactions
Competition
Effect of interaction on species 2
Amensalism ??? Does this Evolve
Neutralnot very interesting until we get to
food webs
Commensalism Scavengers
0
ExploitationTrophic interactions
Commensalism Scavengers
Mutualism Facilitation

5
Interspecific interactionsits all about
acquiring resources
6
Exploitation - 2 trophic-level interactions

• Trophic food
• Individuals of one species need to eat
  individuals of another species
  
• Exploitation might be by killing the prey
  individuals, or by consuming parts of them
  without killing the hosts
  
• One individual benefits, the other is harmed when
  one species acquires resources at the expense of
  another.

• Predator-prey predation
• Herbivore-plant herbivory
• Parasite-host parasitism

7
Examples of 2 trophic-level interactions
8
Consequences of - trophic interactions

• For the upper trophic level
• Consumer (or exploiter)
• Predator, herbivore, parasite
• Individual ? survival, growth, reproduction
• Individual ?fitness
• Population growth ?
• dN/dt 0, N ? N larger when in the presence of
  the lower trophic level

9
Consequences of - trophic interactions

• For the lower trophic level
• Food consumed or exploited
• Prey, plant, host
• Individual ?survival, growth, reproduction
• Individual ?fitness
• Population growth ?
• dN/dt the upper trophic level

10
Trophic levels Food web (chain)upcoming
lectures in Unit III
Upper trophic level
Energy flows
Lower trophic level
Detritivore 0
11
Exploitation terms definitions

• Trophic interaction or
• 2-trophic level interaction
• Population regulation
• definition a density-dependent mechanism in
  which the upper trophic level holds the lower
  trophic level below its carrying capacity

12
2 tropic-level interactions questions?

• What allows predator and prey to coexist (P 0,
  N 0) over time?
  
• Do predators (herbivores, parasites) regulate
  populations of prey (plants, hosts) in nature?

Np
DEFINITION of REGULATION for two trophic levels
A density-dependent process that occurs when a p
redator population decreases a prey population
below its carrying capacity
13
Examples of trophic interactionsWhat are
patterns of trophic interactions in nature?

• Didinium (rotifer) and Paramecium
• Mule deer on the Kaibab Plateau
• Red fox and hare
• Canadian lynx and snowshoe hare
• Lemmings and their predators
• Red Grouse and parasites
• Larch budworm moth larvae and trees
• Humans and parasites
• Prey of humans

14
Didinium v. Paramecium
Rotifer attacking prey
Paramecium (prey)
15
Didinium v. ParameciumGauses laboratory
experiments
Fig. 14.19

• In a simple environment,the Didinium quickly eat
  all of the Paramecium and then starve.
  
• When Gause added hiding places for the
  Paramecium, they hid and the Didinium starved.
  The Paramecium population increased to K.
  
• The only way he could get coexistence was to
  continue to reintroduce each species when it went
  extinct.

16
Conclusion Didinium v. Paramecium

• Gause was disappointed because he could not get
  predator and prey to coexist on their own.
  
• What is the lesson of this experiment for how
  predators and prey interact in Nature (if any)?
  
• How does nature differ from a lab setting?
• How might it be similar to Gauses interventions?

17
Mule deer v. predators
Wolves, Canis lupus
Odocoileus hemionus
Cougar, Puma concolor
Kaibab Plateau AZ
18
Kaibab Plateau and predator control
K of deer 30,000
Removal of wolves, cougars, coyotes
19
Zion Natural Park Mule deer v. cougars
20
Mule deer v. vegetation
Trophic cascade (more in unit III)
21
Sweden Red Fox Vulpes vulpes and Mountain Hare
Lepus timidus
Figs. 14.12-13
22
Prickly pear cactus, Opuntia stricta, introduced
in Australia
Introduced in mid-1800s as ornamental covered
24 million ha by 1930 Following release of Cactob
lastis moth, populations declined from 12,000
individuals/ha to 27 individuals/ha in 2 years
Opuntia however continues to persist in spite of
the moth pathogens pp. 327-8
Cactoblastis cactorum larvae
Fig. 14.11
23
Conclusion mule deer and predators, Swedish
fox and hares

• What was the lesson of these examples (as
  uncontrolled experiments)?
  
• Do predator and prey coexist in Nature?
• Do predators regular prey in Nature?

(P 0, N 0)
What about cactus and moth? Read pp. 327-28
24
Data from Hudson Bay Company
25
Canadian lynx v. snowshoe hare
26
Canadian lynx snowshoe hare
27
Canadian lynx snowshoe hare
Fig. 14.14
Cycle 9-10 yr period
28
A population cycle
period
amplitude
A cycle a regular period amplitude
29
(No Transcript)
30
Lemming example
31
Lemmings v. predators
32
Lemming population cycles
Lemmings v. Stoat
Lemming cycles 3-4 year period
33
Red Grouse v. nematodes in ScotlandLagopus
lagopus scoticus
34
Red Grouse hunted on three moors in Scotland
35
Larch budmoth, in Canada EuropeZeiraphera
diniana
Cycle 9-10 yr period
36
Conclusion from lynx v hare, lemmings, red
grouse, larch and moth?

• Are cycles population regulation?
• Which species is the upper trophic level and
  the regulator in a 3-species food chain?
  
• What generalizations can you make about
  population cycles and why certain interactions
  cause cycling?

Are lynx/hare, lemming cycles caused by the same
mechanisms as mites oranges, cactus moths etc.?
37
Humans parasites
not cycles
Human population irrupts, then is knocked down
38
Fisheries human and their trophic
interactions
39
Atlantic cod fishery
40
Sardine fishery
1800
1960
overfishing
Heavy capitalization
41
Whale fishery
42
Chinook salmon fishery
43
Conclusion Human fisheries

• Do humans regulate their fish prey populations?
• Can humans and their fish prey species coexist?

Cannery Row, Monterrey California, John
Steinbeck collapse of the sardine fishery
44
Outcome of trophic interactions

• Extinction
• Simple systems
• 1 predator-1 prey
• New predators
• Humans
• Invading species

• Coexistence
• Stable equilibrium
• Prey regulated by predator
• Cycles
• Prey still regulated? but not as stable
• Predictable periods

45
How can predators and prey coexist?

• Predators must leave some prey alive for future
  reproductionhow does this happen?
  
• Prudent predator A predator is prudent when
  it intentionally leaves prey for future
  exploitation
  
• a farmer saves some seeds for next years crops
• A fisherman leaves some fish for future
• A hunter doesnt hunt during the breeding season,
  etc etc.

46
Are truisims about Nature true?

• Nature is balanced
• Individuals withhold reproduction so that there
  will always be enough for everybody
  
• Predators withhold predation so that they dont
  drive prey to extinction
  
• Good parasites dont kill their host
• Grazing herbivores are good for plants

47
Salmon v. humans

• A tale of two examples
• Sustainable fishery versus a crashing,
  overexploited fishery
  
• Predators can be prudent when they have
  territories
  
• Vs. The Tragedy of the Commons

48
Hoopa Valley Yurok Tribes
49
Early settlers use of salmon
Whos using this salmon? Does it pay to leave s
ome salmon for the future?
Cases packed
50
(No Transcript)
51
Tragedy of the Commons

• Phrase coined in a highly influential essay by
  Garrett Hardin
  

When no one owns the commons there is no
motivation for stewardhip (prudence).
52
Orange/Red High productivity Green
Intermediate Blue low
Who owns the open ocean?? How can it be managed
with prudence?
53
Predator-prey coexistence

• How can (non-prudent) predators coexist with
  their prey in nature?
  
• Predators are inefficient
• Predators are constrained by costs or ability to
  catch prey

54
Applying foraging ecologyBears vs. seals

• Bears eat the older, fatter pups but avoid
  reproductive adults

55
Predator-prey coexistence

• How can (non-prudent) predators coexist with
  their prey in nature?
  
• In real systems, predation is often
  inefficient.
  
• Predator-prey coevolution
• Prey populations evolve so that prey are more
  difficult for predators to catch, kill and
  digest
  
• But predator populations evolve to overcome prey
  defenses.
  
• RED QUEEN EFFECT

56
Red Queen effect
"Well, in our country," said Alice, still panting
a little, "you'd generally get to somewhere
else-if you ran very fast for a long time as
we've been doing."
"A slow sort of country!" said the Queen. "Now,
here, you see, it takes all the running you can
do, to keep in the same place. If you want to get
somewhere else, you must run at least twice as
fast as that!
In 2-trophic-level coevolution, the prey
population evolves traits to deter the predator,
and the predator population evolves traits to
overcome the defenses. Thus the two populations
run from each other and stay in the same
evolutionary place.
57
Chemical defenses
58
Plants fight back with chemicals to deter
herbivores from eating them
Nightshade
Datura Jimpson weed
Loco weed
59
Predator-prey coexistence

• How can (non-prudent) predators coexist with
  their prey in nature?
  
• Nature is complex
• Hiding places for prey (literally)
• Metapopulations populations can hide from
  predators
  
• Eventually predators find unexploited populations
  and may drive them to extinction
  
• However, prey individuals continually disperse
  and found new population where there are no
  predators.
  
• Example is the mite-orange universe of Huffaker
  or Cactus moth-Opuntia populations in Australia
  
• Alternative choices of prey
• Can stabilize predator-prey interactions by
  taking pressure off of each prey species

60
Refugia from predation
61
Spatial refuges mussels above the starfishs
high tide limit
62
Safety in numbers a refuge at high densities
63
Safety in numbers Bird flocks

• Sturnus vulgaris, the common European Starling
  being stalked by a falcon

64
Periodical Cicadas -Predator avoidance or
satiation
Fig. 14.24