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Species interactions I - Competition
1 Levels of Study ■ Organismal ■ Population ■ Community ■ Ecosystem
■ Particular species can exist in a particular range of Hey! circumstances What s the ■ This range is influenced by the presence of other species - big idea!!! e.g. competition ■ Various outcomes of competition are possible and can be documented ■ Particular outcomes depend on nature of species involved, the environment, and the timescale being considered
2 Types of species interactions Effect on A B
◆Competition (AÛB) - - ◆Predation (AÞB) + - ◆Parasitism (AÞB) + - ◆Mutualism (AÛB) + +
Essential Questions ■What regulates population size? ■What regulates species number? ■What regulates the distribution of species?
3 Antagonistic interactions ■ Can regulate population sizes ■ Usually increase in severity with N ■ Density dependent ◆Increased N influences b and d
◆Therefore influences ractual ◆Recall logistic growth
Competition may be ... ■ Intraspecific ◆Individuals within a species compete for limiting resources ◆This is what we ve focussed on
4 Competition may be ... ■ Intraspecific ■ Interspecific ◆Individuals of different species compete for limiting resources
Interspecific Competition ■ But first … ◆What is a niche? ■An n-dimension description of resources, habitat, and lifestyle of a species
5 Suppose I find the following …
Fig. 53.6
Fundamental vs. Realized Niche
See fig. 53.6
6 Fundamental vs. Realized Niche ■ Fundamental niche - niche a species could potentially occupy (in the absence of competition)
■Realized niche - niche a species actually does occupy with competition
Interspecific Competition ■ Species that use the same resource(s) can affect each other s growth, survival, and reproduction ■Exploitation ◆differential abilities to use or extract the resource
7 Interspecific Competition ■ Species that use the same resource(s) can affect each other s growth, survival, and reproduction ■Exploitation ■Interference ◆ one organism directly affects the ability of another organism to obtain resources
Competitive exclusion principle ■ Interspecific competition leads to a decrease in each species K (potentially to 0) ■Two species occupying exactly the same niche can not coexist ◆will differ in their competitive ability ◆one will eventually exclude the other
8 Documenting Interspecific competition
■ Need an experiment ◆How would you test this?
Documenting Interspecific competition
■ Need an experiment ◆How would you test this? ◆ Is the equilibrium population size (K) reduced in the presence of another species?
9 Documenting Interspecific competition
■ Need an experiment ◆How would you test this? ◆ Is the equilibrium population size (K) reduced in the presence of another species? ◆ Are b and d affected by the presence of another species?
Documenting Interspecific competition Example - P. aurelia vs. P. caudatum
Fig. 53.3
10 Documenting Interspecific competition Example - Ants vs. rodents
vs.
Outcomes of Interspecific competition ■ I: Competitive exclusion ◆ Two species with identical niches can not coexist.
53.3,4
11 Outcomes of Interspecific competition ■ I: Competitive exclusion ■II: Coexistence ◆Use of resources (niche) different ◆Realized niches ◆Resource Partitioning Not in text
Outcomes of Interspecific competition ■ I: Competitive exclusion ■II: Coexistence ◆ Use of resources (niche) different ✦E.g. Tribolium vs. Oryzaephilis ✦E.g. Anolis Lizards
12 Outcomes of Interspecific competition
Not in text
Just Flour Flour plus tubes
Outcomes of Interspecific competition
13 Outcomes of Interspecific competition
Outcomes of Interspecific competition ■ I: Competitive exclusion ■ II: Coexistence ◆ Use of resources (niche) different ◆ Heterogeneity of habitat important (implications for monoculture, forest management)
14 Consider …
■ The San Francisco Bay mudflats where Ilyanassa Photo credit: obsoleta is now found were once occupied by the Anthony Fisher native hornsnail Cerithidea californica. Race (1982) describes how each spring the two populations of these snails collide in the lower marsh channels. By mid-summer Ilyanassa obsoleta has restricted the native hornsail to the upper channels and shallow pools in the upper marsh through a combination of egg predation and direct competitive interference. The high marsh pools (also called salt pannes) are too salty for Ilyanassa obsoleta, and thus provide a habitat refuge for the native snail. http://www.exoticsguide.org/ilyanassa_obsoleta
Outcomes of Interspecific competition Niche Differentiation (and Character displacement)
53.7
15 Outcomes of Interspecific competition Niche Differentiation (Character displacement)
See Fig. 53.8
Outcomes of Interspecific competition ■ I: Competitive exclusion ■ II: Coexistence ■ III: Niche Differentiation ◆An evolutionary response to competition ◆Ghost of competition past?
16 Summary ■ Competition ◆Intraspecific vs. Interspecific ■ The Niche ◆ Fundamental vs. realized ■Types of competition ◆Exploitation vs. Interference ■Outcomes of competition ◆ I: Competitive exclusion ◆ II: Coexistence ◆ III: Niche Differentiation and Character Displacement
Species interactions II - Predation
17 What is predation? ■ A +/- interaction in which one organism feeds on another ◆E.g. animals on each other, animals on plants (herbivory). Exploiters of others ◆We ll include parasitism, parasitoidism
Why is Predation Important? ■ Can influence population size and distribution of prey ◆Management implications ■ Can influence community organization ◆Species coexistence and stability - Later ■ Is an important force of natural selection
18 Do predators control prey populations? ■Seems obvious, but this is controversial in many cases
Do predators control prey populations? ■Seems obvious, but this is controversial in many cases ◆Additive vs. Compensatory Mortality ◆Important management implications - e.g. wolves ◆Do they affect population sizes of caribou, moose? If so, to what degree?
19 Do predators control prey populations? ■Seems obvious, but this is controversial in many cases ■Examples ◆Introduction of predators
Do predators control prey populations? ■Seems obvious, but this is controversial in many cases ■Examples ◆Introduction of predators
20 Do predators control prey populations? ■Seems obvious, but this is controversial in many cases ■Examples ◆Introduction of predators
Do predators control prey populations? ■Seems obvious, but this is controversial in many cases ■Examples ◆Introduction of predators
21 Do predators control prey populations? ■Seems obvious, but this is controversial in many cases ■Examples ◆Introduction of predators ✦Prickly Pear and Cactus moths in Australia ✦Prickly pear introduced in 1830 ✦Covered 40,000 km2 by 1880 ✦1929: 2 million Cactus moth eggs introduced ✦1935: Prickly pear reduced to 0.2%
Do predators control prey populations? ■Seems obvious, but this is controversial in many cases ■Examples ◆Dingos and kangaroos ◆Design an experiment
22 Do predators control prey populations? ■Kangaroos much more abundant in areas where dingos have been excluded
Predation in the lab ■Tough to get coexistence in the lab ◆Simple system: Predators tend to eat all the prey - E.g. Paramecium, Didinium
23 Predation in the lab ■Tough to get coexistence in the lab ◆With refugia: Predators drive prey to very low abundance, then die out. Paramecium, Didinium ■Refugia Sound familiar? What have we added?
What promotes predator/prey Coexistence?
24 What promotes predator/prey Coexistence?
What promotes predator/prey Coexistence?
25 Habitat Heterogeneity
What promotes predator/prey Coexistence? ■If predators are controlling prey populations, several factors may allow long term coexistence, including ◆Habitat heterogeneity - Cactus/moth,Mites ◆Refugia - Didinium/Paramecium (potentially) ◆Prey switching - Predators switch to other prey when prey abundance is low. Dingo
26 What, besides predators, could control populations? ■Predator effect could be minor if ◆Predator densities are low. E.g. predators have territories that enforce low density. ◆Predators mainly take prey destined to die without reproducing anyway (old, infirm) ◆Harvesting the doomed. Limited resources for prey mean most will die anyway. E.g. muskrats, mink - Compensatory Mortality
What, besides predators, could control populations? ■Mink prey on muskrats
◆A major cause of muskrat death ◆But, does it limit population size?
27 What, besides predators, could control populations? ■Intra- or Interspecific competition may be more important than predation ◆May be a reflection of simple abundance
Sea Lions and Salmon
28 Sea Lions and Salmon
Why don t plants get wiped out by herbivores? ■Prey may defend themselves! ◆Plants, herbivores, and carnivores
29 Plants are not passive! ■ Physical defense ◆Spines, fibers, stings, etc. ◆Constitutive defenses
Plants are not passive! ■ Physical defense ■ Chemical defense - Secondary compounds, E.g. ◆Tannins - reduce digestibility of leaf ◆Nicotine, caffeine, opium, strychnine, digitalis - distasteful or poisonous ■Constitutive or inducible
30 Plants are not passive! ■ Physical defense ■ Chemical defense - Secondary compounds ■Impose a cost to the plant! ◆At low herbivore abundance, selection reduces the level of defense ◆Or, induction may be reduced ◆A reprieve for herbivores
Chemical Defense in plants The herbivores respond ■ May develop tolerance to the plant defense and actually specialize on plant ◆Heliconius butterflies and passion flowers ◆Gypsy moths are tannin tolerant
31 Chemical Defense in plants The herbivores respond ■ Some herbivores even store toxic plant compounds for their own defense ◆E.g. Monarch butterflies and milkweed
■Arms Races: The Red Queen Hypothesis
Chemical Defense in plants The herbivores respond ■ Some herbivores even store toxic plant compounds for their own defense ◆E.g. Beavers, Cottonwoods, leaf beetles ◆Fig. 53.13
■Arms Races: The Red Queen Hypothesis
32 Top Down and Bottom up Plants, Hares, and Lynx ■ Hares show a regular cycle of population size - period about 10 years ◆What causes this?
52.11
Top Down and Bottom up Plants, Hares, and Lynx ■ Hares show a regular cycle of population size - period about 10 years ■Traditional view ◆Lynx have a correlated cycle
33 Top Down and Bottom up Plants, Hares, and Lynx ■ Hares show a regular cycle of population size - period about 10 years ■Traditional view ◆Lynx have a correlated cycle ◆Increased hare populations -> ◆Increased lynx populations (time lag) -> ◆Decreased hare populations -> ◆Decreased lynx populations -> etc.
Top Down and Bottom up Plants, Hares, and Lynx ■ Hares show a regular cycle of population size - period about 10 years ◆What causes this? ■Traditional view - Challenged by recent data ◆Hares cycle even in the absence of lynx!
34 Top Down and Bottom up Plants, Hares, and Lynx ■ Increase in hare population leads to ◆Decrease in plant availability ◆Decrease in plant quality (plant defense) ◆Increase in Lynx population ■ Hares decline due to combined effects of ◆Lower food abundance/quality ◆Increasing predation
Top Down and Bottom up Plants, Hares, and Lynx ■ Hare fluctuations influenced by both resource availability and predation ■Lynx fluctuations influenced by prey availability ■Plant responses are partly driving the system
35 Summary ■ Predation: a +/- interaction ■ Predation may be important for ◆Regulating population size, community structure, and as a force of natural selection ■ In some cases, predation clearly controls prey population size - e.g. Kangaroos ◆Long term control difficult to achieve in lab ◆Reflects factors such as heterogeneity, prey switching
Summary ■ In other cases, predation a minor factor compared to competition - e.g. muskrats ■ Plants, as prey, evolve their own response to predation and may regulate population size from the bottom up ◆Physical, chemical defenses ◆Herbivores respond - the Red Queen ■ The plant, the hare, and the lynx ◆A little bit of everything
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