species diversity
DESCRIPTION
Species diversity. Ecological communities differ in species number and composition tropics > temperate remote islands < large islands continents > islands. Species diversity. Comprised of species richness : number of species present heterogeneity of species equitability or evenness - PowerPoint PPT PresentationTRANSCRIPT
![Page 1: Species diversity](https://reader034.vdocuments.net/reader034/viewer/2022051215/56814c24550346895db928aa/html5/thumbnails/1.jpg)
1
Species diversity
• Ecological communities differ in species number and composition– tropics > temperate– remote islands < large islands– continents > islands
![Page 2: Species diversity](https://reader034.vdocuments.net/reader034/viewer/2022051215/56814c24550346895db928aa/html5/thumbnails/2.jpg)
2
Species diversity
• Comprised of– species richness: number of species present– heterogeneity of species
• equitability or evenness• relative abundance of each species present in the
community
![Page 3: Species diversity](https://reader034.vdocuments.net/reader034/viewer/2022051215/56814c24550346895db928aa/html5/thumbnails/3.jpg)
3
Measurement of species diversity
• Species richness– number of species present in community– first and oldest concept of diversity– simplest estimate of diversity– only residents are counted– treats common and rare species with the
same weight
![Page 4: Species diversity](https://reader034.vdocuments.net/reader034/viewer/2022051215/56814c24550346895db928aa/html5/thumbnails/4.jpg)
4
Measurement of species diversity
• Heterogeneity of species– uses relative abundance to give more weight
to common species
– possibilities in a 2-species community:
Comm 1 Comm 2Species A 99 50Species B 1 50
100 100
![Page 5: Species diversity](https://reader034.vdocuments.net/reader034/viewer/2022051215/56814c24550346895db928aa/html5/thumbnails/5.jpg)
5
Measurement of species diversity
• Shannon-Wiener diversity function
H' = - (pi) [ln(pi)]
H’ = Shannon-Wiener index of species diversity
s = number of species in community
pi = proportion of total abundance represented by ith species
s
![Page 6: Species diversity](https://reader034.vdocuments.net/reader034/viewer/2022051215/56814c24550346895db928aa/html5/thumbnails/6.jpg)
6
Shannon-Wiener diversity index
Community 1
Species N pi ln(pi) pi[(ln(pi)]
A 99
B 1
Community 2
Species N pi ln(pi) pi[(ln(pi)]
A 50
B 50
![Page 7: Species diversity](https://reader034.vdocuments.net/reader034/viewer/2022051215/56814c24550346895db928aa/html5/thumbnails/7.jpg)
7
Shannon-Wiener diversity index
Community 1
Species N pi ln(pi) pi[(ln(pi)]
A 99 0.99 -0.010 -0.010
B 1 0.01 -4.605 -0.046
100 1.00 -0.056
H’ 0.056
Community 2
Species N pi ln(pi) pi[(ln(pi)]
A 50 0.50 -0.693 -0.347
B 50 0.50 -0.693 -0.347
100 1.00 -0.694
H’ 0.694
![Page 8: Species diversity](https://reader034.vdocuments.net/reader034/viewer/2022051215/56814c24550346895db928aa/html5/thumbnails/8.jpg)
8
Measurement of species diversity
• Shannon-Wiener diversity function– values range from near zero to ???– increased values indicate increased diversity– index has no units; value only as comparison
between at least two communities
![Page 9: Species diversity](https://reader034.vdocuments.net/reader034/viewer/2022051215/56814c24550346895db928aa/html5/thumbnails/9.jpg)
9
Species diversity
• What increases species diversity (H’)?– increasing the number of species in the
community (s)– increasing the equitability of the abundances
of each species in the community
![Page 10: Species diversity](https://reader034.vdocuments.net/reader034/viewer/2022051215/56814c24550346895db928aa/html5/thumbnails/10.jpg)
10
Evenness
• Measurement of equitability among species in the community
• Pielou evenness
E = H’ / HmaxE = Pielou evenness
H’ = calculated Shannon-Wiener diversityHmax = ln(s) [species diversity under maximum equitability conditions]
– values range from near zero to 1
![Page 11: Species diversity](https://reader034.vdocuments.net/reader034/viewer/2022051215/56814c24550346895db928aa/html5/thumbnails/11.jpg)
11
Diversity and evenness
Community 1 Community 2
s 2 2
H’ 0.056 0.694
Hmax 0.693 0.693
E 0.081 1.000
![Page 12: Species diversity](https://reader034.vdocuments.net/reader034/viewer/2022051215/56814c24550346895db928aa/html5/thumbnails/12.jpg)
12
Community 1
Species N pi ln(pi) pi[(ln(pi)]
A 62
B 97
C 110
D 84
E 16
Practice problem
![Page 13: Species diversity](https://reader034.vdocuments.net/reader034/viewer/2022051215/56814c24550346895db928aa/html5/thumbnails/13.jpg)
13
Community 2
Species N pi ln(pi) pi[(ln(pi)]
A 88
B 10
C 0
D 211
E 27
Practice problem
![Page 14: Species diversity](https://reader034.vdocuments.net/reader034/viewer/2022051215/56814c24550346895db928aa/html5/thumbnails/14.jpg)
14
Practice problem
Community 1 Community 2
s
H’
Hmax
E
![Page 15: Species diversity](https://reader034.vdocuments.net/reader034/viewer/2022051215/56814c24550346895db928aa/html5/thumbnails/15.jpg)
15
Species diversity indices
![Page 16: Species diversity](https://reader034.vdocuments.net/reader034/viewer/2022051215/56814c24550346895db928aa/html5/thumbnails/16.jpg)
16
Commonness, rarity and dominance
• Preston’s log normal distribution model– a few common species with high
abundances– many rare species with low abundances
![Page 17: Species diversity](https://reader034.vdocuments.net/reader034/viewer/2022051215/56814c24550346895db928aa/html5/thumbnails/17.jpg)
17
Commonness, rarity and dominance
• MacArthur’s broken stick model– random breaks in a stick log normal
distribution of pieces– results in a few large pieces and many small
pieces
![Page 18: Species diversity](https://reader034.vdocuments.net/reader034/viewer/2022051215/56814c24550346895db928aa/html5/thumbnails/18.jpg)
18
Commonness, rarity and dominance
• Community organization– model 1
• a few very common species• many rare species
– model 2• a few very common and very rare species• most species of intermediate abundance
![Page 19: Species diversity](https://reader034.vdocuments.net/reader034/viewer/2022051215/56814c24550346895db928aa/html5/thumbnails/19.jpg)
19
Fig. 22.1, p. 435: Relative abundance of Lepidoptera captured in a light trap in England (6814 individuals representing 197 species).
![Page 20: Species diversity](https://reader034.vdocuments.net/reader034/viewer/2022051215/56814c24550346895db928aa/html5/thumbnails/20.jpg)
20
Biogeography
• Observations of relationships between– area and number of species– distance from source
• Island biogeography– E.O. Wilson and Robert MacArthur
![Page 21: Species diversity](https://reader034.vdocuments.net/reader034/viewer/2022051215/56814c24550346895db928aa/html5/thumbnails/21.jpg)
21
Island biogeography
• Island communities: well-defined, captive
• Variables– size– degree of remoteness– elevation
• Simple community structure
• Increase in area increase in number of species
![Page 22: Species diversity](https://reader034.vdocuments.net/reader034/viewer/2022051215/56814c24550346895db928aa/html5/thumbnails/22.jpg)
22
Island biogeography
• Habitats considered as “insular” because they are isolated from other communities– caves– mountain tops– some peninsulas– wildlife or game preserves
![Page 23: Species diversity](https://reader034.vdocuments.net/reader034/viewer/2022051215/56814c24550346895db928aa/html5/thumbnails/23.jpg)
23
Fig. 24.14, p. 502: Number of land-plant species on the Galapagos Islands in relation to the area of the island.
![Page 24: Species diversity](https://reader034.vdocuments.net/reader034/viewer/2022051215/56814c24550346895db928aa/html5/thumbnails/24.jpg)
24
Fig. 24.15, p. 503: Species-area curve for amphibians and reptiles of the West Indies.
![Page 25: Species diversity](https://reader034.vdocuments.net/reader034/viewer/2022051215/56814c24550346895db928aa/html5/thumbnails/25.jpg)
25
Island biogeography
• Relationship between remoteness and number of species– increase distance from mainland decrease
number of species– number of species present is dependent on
immigration from mainland• rate is a function of the number of species already
present on the island• number of species present = balance between
immigration and extinction
![Page 26: Species diversity](https://reader034.vdocuments.net/reader034/viewer/2022051215/56814c24550346895db928aa/html5/thumbnails/26.jpg)
26
Fig. 24.17, p. 504: Equilibrium model for biota on a single island.
![Page 27: Species diversity](https://reader034.vdocuments.net/reader034/viewer/2022051215/56814c24550346895db928aa/html5/thumbnails/27.jpg)
27
Fig. 24.18, p. 504: Equilibrium model for biota on several islands of different size and remoteness.
![Page 28: Species diversity](https://reader034.vdocuments.net/reader034/viewer/2022051215/56814c24550346895db928aa/html5/thumbnails/28.jpg)
28
Island biogeography
• Small species are found on more islands than are large species
• Number of herbivore species > carnivores
• Number of generalist herbivore species > specialist herbivores
![Page 29: Species diversity](https://reader034.vdocuments.net/reader034/viewer/2022051215/56814c24550346895db928aa/html5/thumbnails/29.jpg)
29
Island biogeography
• Species:area relationship– log : log relationship– 10-fold decrease in area 50% decrease in
number of species
![Page 30: Species diversity](https://reader034.vdocuments.net/reader034/viewer/2022051215/56814c24550346895db928aa/html5/thumbnails/30.jpg)
30
Island biogeography
• Species:area relationship
![Page 31: Species diversity](https://reader034.vdocuments.net/reader034/viewer/2022051215/56814c24550346895db928aa/html5/thumbnails/31.jpg)
31
Latitudinal diversity gradients
• Abundance and diversity patterns– latitude– elevation– mountainsides– peninsulas
![Page 32: Species diversity](https://reader034.vdocuments.net/reader034/viewer/2022051215/56814c24550346895db928aa/html5/thumbnails/32.jpg)
32
Fig. 22.5, p. 438: Number of tree species in Canada and U.S.
![Page 33: Species diversity](https://reader034.vdocuments.net/reader034/viewer/2022051215/56814c24550346895db928aa/html5/thumbnails/33.jpg)
33
Fig. 22.6, p. 439: Number of species of land birds in North and Central America.
![Page 34: Species diversity](https://reader034.vdocuments.net/reader034/viewer/2022051215/56814c24550346895db928aa/html5/thumbnails/34.jpg)
34
Fig. 22.7, p. 440: Number of species of calanoid copepods in top 50 m of transect from tropical Pacific to Arctic Ocean.
![Page 35: Species diversity](https://reader034.vdocuments.net/reader034/viewer/2022051215/56814c24550346895db928aa/html5/thumbnails/35.jpg)
35
Fig. 22.9, p. 440: Number of species of mammals in continental North America.
![Page 36: Species diversity](https://reader034.vdocuments.net/reader034/viewer/2022051215/56814c24550346895db928aa/html5/thumbnails/36.jpg)
36
Fig. 22.10, p. 440: Species richness of mammals in North and South America in relation to latitude.
![Page 37: Species diversity](https://reader034.vdocuments.net/reader034/viewer/2022051215/56814c24550346895db928aa/html5/thumbnails/37.jpg)
37
Latitudinal diversity gradients
• Tree species– Malaysia (4
acres): 227– Michigan (4
acres): <15
• Ant species– Brazil: 222– Trinidad: 134– Cuba: 101– Utah: 63– Alaska: 7
![Page 38: Species diversity](https://reader034.vdocuments.net/reader034/viewer/2022051215/56814c24550346895db928aa/html5/thumbnails/38.jpg)
38
Latitudinal diversity gradients
• Snake species– Mexico: 293– U.S.: 126– Canada: 22
• Fish species– Amazon R: >1000– Central American
rivers: 450– Great Lakes: 172
![Page 39: Species diversity](https://reader034.vdocuments.net/reader034/viewer/2022051215/56814c24550346895db928aa/html5/thumbnails/39.jpg)
39
Latitudinal gradient hypotheses
• History (time)
• Spatial heterogeneity
• Competition
• Predation
• Productivity
• Environmental stability (climate)
• Disturbance
![Page 40: Species diversity](https://reader034.vdocuments.net/reader034/viewer/2022051215/56814c24550346895db928aa/html5/thumbnails/40.jpg)
40
Latitudinal gradient hypotheses
• History (time) hypothesis– tropical habitats older, more stable– support for
• geological past of temperate less constant than tropics due to glaciation
• all communities diversify with time
– argument against• as glaciers moved in, species moved south to
escape• history hypothesis can not be tested
![Page 41: Species diversity](https://reader034.vdocuments.net/reader034/viewer/2022051215/56814c24550346895db928aa/html5/thumbnails/41.jpg)
41
Latitudinal gradient hypotheses
• Spatial heterogeneity hypothesis– higher diversity in tropics due to increase in
number of potential habitats environmental complexity moving away from
equator• macro level: e.g., topographic features• micro level: e.g., particle size, vegetation
complexity
![Page 42: Species diversity](https://reader034.vdocuments.net/reader034/viewer/2022051215/56814c24550346895db928aa/html5/thumbnails/42.jpg)
42
Latitudinal gradient hypotheses
• Spatial heterogeneity hypothesis– Hutchinson’s n-dimensional niche
specialization– types of diversity defined by spatial
heterogeneity• within-habitats ( diversity)• between-habitats ( diversity)
![Page 43: Species diversity](https://reader034.vdocuments.net/reader034/viewer/2022051215/56814c24550346895db928aa/html5/thumbnails/43.jpg)
43
Diversity defined by spatial heterogeneity
Between habitat diversity ()
Temperate Tropical
No. species per habitat 10 10
No. different habitats 10 50
Within-habitat diversity ()
Temperate Tropical
No. species per habitat 10 50
No. different habitats 10 10
![Page 44: Species diversity](https://reader034.vdocuments.net/reader034/viewer/2022051215/56814c24550346895db928aa/html5/thumbnails/44.jpg)
44
Latitudinal gradient hypotheses
• Competition hypothesis– less competition in temperate and polar
environments compared to tropics because these populations are more regulated by extreme environmental conditions than by biological factors
– populations maintained <K due to weather, etc. and major sources of mortality are abiotic
– since population sizes small, decreased competition for resources
![Page 45: Species diversity](https://reader034.vdocuments.net/reader034/viewer/2022051215/56814c24550346895db928aa/html5/thumbnails/45.jpg)
45
Latitudinal gradient hypotheses
• Competition hypothesis– no weather extremes in tropics,
populations can increase to densities at which competition for resources is necessary
– promotes species diversity through specialization resource partitioning
and diversity higher in tropics due to organisms being more specialized to habitats
![Page 46: Species diversity](https://reader034.vdocuments.net/reader034/viewer/2022051215/56814c24550346895db928aa/html5/thumbnails/46.jpg)
46
Fig. 22.14a, p. 447. Niche breadth versus niche overlap determined by competition within the community.
![Page 47: Species diversity](https://reader034.vdocuments.net/reader034/viewer/2022051215/56814c24550346895db928aa/html5/thumbnails/47.jpg)
47
Latitudinal gradient hypotheses
• Predation hypothesis– increased species diversity in tropics is
function of increased number of predators that regulate the prey species at low densities
– decreases competition among prey species– allows coexistence of prey species and
potential for new additions
![Page 48: Species diversity](https://reader034.vdocuments.net/reader034/viewer/2022051215/56814c24550346895db928aa/html5/thumbnails/48.jpg)
48
Fig. 22.16, p. 449. Janzen-Connell model for increased diversity of tropical rainforest trees: seed predation versus distance of seed from tree versus seed survival.
![Page 49: Species diversity](https://reader034.vdocuments.net/reader034/viewer/2022051215/56814c24550346895db928aa/html5/thumbnails/49.jpg)
49
Latitudinal gradient hypotheses
• Predation hypothesis– there is more selective pressure on prey
evolving avoidance mechanisms than in becoming better competitors
– cropping principle• remove predators and prey start competing• predation increases diversity by reducing
intraspecific competition among prey species
![Page 50: Species diversity](https://reader034.vdocuments.net/reader034/viewer/2022051215/56814c24550346895db928aa/html5/thumbnails/50.jpg)
50
Community anchored by keystone starfish Heliaster in northern Gulf of California.
![Page 51: Species diversity](https://reader034.vdocuments.net/reader034/viewer/2022051215/56814c24550346895db928aa/html5/thumbnails/51.jpg)
51
Latitudinal gradient hypotheses
• Predation hypothesis– cropping principle in lakes
• top predators (fish) feed on zooplankton• if fish are removed community diversity
decreases, becomes dominated by a few species of large, grazing zooplankton
• add fish diversity of small zooplankton and their invertebrate predators increases
![Page 52: Species diversity](https://reader034.vdocuments.net/reader034/viewer/2022051215/56814c24550346895db928aa/html5/thumbnails/52.jpg)
52
Latitudinal gradient hypotheses
• Productivity hypothesis– tropics support a greater number of species
because more resources are available, allowing for more specialization
– in general: production diversity– exceptions
• marshes: high production, relatively low diversity• deserts: low production, high diversity
![Page 53: Species diversity](https://reader034.vdocuments.net/reader034/viewer/2022051215/56814c24550346895db928aa/html5/thumbnails/53.jpg)
53
Latitudinal gradient hypotheses
• Environmental stability (climatic) hypothesis– annual climate in tropics more stable than
temperate or polar climates– constant climate finer specializations and
adaptations, shallower niches– tropical species number of broods / year
potential for evolutionary change rate of speciation
![Page 54: Species diversity](https://reader034.vdocuments.net/reader034/viewer/2022051215/56814c24550346895db928aa/html5/thumbnails/54.jpg)
54
Latitudinal gradient hypotheses
• Environmental stability (climatic) hypothesis– high diversity habitats generally found in
stable climates; low diversity habitats associated with severe and/or unpredictable climates
![Page 55: Species diversity](https://reader034.vdocuments.net/reader034/viewer/2022051215/56814c24550346895db928aa/html5/thumbnails/55.jpg)
55
Latitudinal gradient hypotheses
• Disturbance hypothesis– if community disturbance frequency is very
high local extinction of species species diversity
– if community disturbance frequency is very low competitive exclusion by dominant species species diversity
![Page 56: Species diversity](https://reader034.vdocuments.net/reader034/viewer/2022051215/56814c24550346895db928aa/html5/thumbnails/56.jpg)
56
Latitudinal gradient hypotheses
• Disturbance hypothesis– intermediate disturbance hypothesis
• moderate disturbance maximizes diversity• leads to patches at local level
– intermediate disturbance high species diversity in some communities (not all)
![Page 57: Species diversity](https://reader034.vdocuments.net/reader034/viewer/2022051215/56814c24550346895db928aa/html5/thumbnails/57.jpg)
57
Fig. 22.20, p. 453. Model for intermediate disturbance hypothesis.
![Page 58: Species diversity](https://reader034.vdocuments.net/reader034/viewer/2022051215/56814c24550346895db928aa/html5/thumbnails/58.jpg)
58
Fig. 22.21, p. 453. Effect of periwinkle grazing on algae diversity.
![Page 59: Species diversity](https://reader034.vdocuments.net/reader034/viewer/2022051215/56814c24550346895db928aa/html5/thumbnails/59.jpg)
59
Fig. 22.21, p. 453. Effect of periwinkle grazing on algae diversity.
Community dominated by one algal species
Predator limits number of possible algal species
![Page 60: Species diversity](https://reader034.vdocuments.net/reader034/viewer/2022051215/56814c24550346895db928aa/html5/thumbnails/60.jpg)
60
Basic concepts related to energy flow and trophic structure
• Energy moves through community and is lost as heat
• Nutrients move through the community in cycles and are retained
![Page 61: Species diversity](https://reader034.vdocuments.net/reader034/viewer/2022051215/56814c24550346895db928aa/html5/thumbnails/61.jpg)
61
Basic concepts related to energy flow and trophic structure
• Niche– sum of all parameters that enable an organism
to live in its biotic and abiotic environments• competition, food gathering, predator escape, mate
location, reproduction, etc.• temperature, moisture, nutrients, soil structure,
salinity, etc.
– Hutchinsonian niche: n-dimensional hypervolume
![Page 62: Species diversity](https://reader034.vdocuments.net/reader034/viewer/2022051215/56814c24550346895db928aa/html5/thumbnails/62.jpg)
62
Basic concepts related to energy flow and trophic structure
• Trophic level– Lindeman (1942)
• classification of animals according to location in lake
• lake trophic groups– benthic– demersal– plankton– nekton
![Page 63: Species diversity](https://reader034.vdocuments.net/reader034/viewer/2022051215/56814c24550346895db928aa/html5/thumbnails/63.jpg)
63
Basic concepts related to energy flow and trophic structure
• Trophic level– Lindeman (1942)
• described food chain with primary producers at base and other trophic levels of animals based on feeding relationships
• more accurately described as food web, since few organisms other than plants occupy only one feeding level
![Page 64: Species diversity](https://reader034.vdocuments.net/reader034/viewer/2022051215/56814c24550346895db928aa/html5/thumbnails/64.jpg)
64
Food webs and energy flow
• Trophic levels– ecosystem feeding levels– biomass and usable energy as level – most systems support only four trophic levels– aquatic communities have slightly longer food
chains than terrestrial communities– ultimate food chain length limited by inefficiency
of energy transfer from one trophic level to the next
![Page 65: Species diversity](https://reader034.vdocuments.net/reader034/viewer/2022051215/56814c24550346895db928aa/html5/thumbnails/65.jpg)
65
Food webs and energy flow
• Food chains– sequence of organisms where each is the
food source for the next
• Food webs– represent energy flow through ecosystem
![Page 66: Species diversity](https://reader034.vdocuments.net/reader034/viewer/2022051215/56814c24550346895db928aa/html5/thumbnails/66.jpg)
66
Trophic levels
Tertiary consumers (top carnivores)
Secondary consumers (carnivores)
Primary consumers (herbivores)
Primary producers (plants)
![Page 67: Species diversity](https://reader034.vdocuments.net/reader034/viewer/2022051215/56814c24550346895db928aa/html5/thumbnails/67.jpg)
67
Heat Heat Heat Heat
Heat
Heat
Heat
First TrophicLevel
Second TrophicLevel
Third TrophicLevel
Fourth TrophicLevel
Solarenergy
Producers(plants)
Primaryconsumers(herbivores)
Tertiaryconsumers
(top carnivores)
Secondaryconsumers(carnivores)
Detritivores(decomposers and detritus feeders)
Heat Heat
Food chain model
![Page 68: Species diversity](https://reader034.vdocuments.net/reader034/viewer/2022051215/56814c24550346895db928aa/html5/thumbnails/68.jpg)
68
Figure 23.6, p. 465. Hypothetical food web model.
![Page 69: Species diversity](https://reader034.vdocuments.net/reader034/viewer/2022051215/56814c24550346895db928aa/html5/thumbnails/69.jpg)
69
Food web terminology
• Top predators: species eaten by nothing else in the food web• Basal species: species that feed on nothing within the food web• Intermediate species: species that have both predators and prey
within the food web• Trophic species: groups of organisms that have identical sets of
predators and prey• Cycles within food web: which species eat which other species• Interaction: any feeding relationship within food web• Connectance: number of actual interactions in food web divided by
number of possible interactions• Linkage density: average number of interactions per species in the
food web• Omnivores: species that feed on more than one trophic level• Compartments: groups of species with strong linkages among group
members but weak linkages to other groups of species
![Page 70: Species diversity](https://reader034.vdocuments.net/reader034/viewer/2022051215/56814c24550346895db928aa/html5/thumbnails/70.jpg)
70
Figure 23.8, p. 467. Distribution of food chain lengths in the Ythan Estuary, NE Scotland.
95 species
5518 food chain lengths counted
![Page 71: Species diversity](https://reader034.vdocuments.net/reader034/viewer/2022051215/56814c24550346895db928aa/html5/thumbnails/71.jpg)
71
Food web of a rocky intertidal community, northern Gulf of California (after Paine 1966).
Producers Producers Producers Producers
![Page 72: Species diversity](https://reader034.vdocuments.net/reader034/viewer/2022051215/56814c24550346895db928aa/html5/thumbnails/72.jpg)
72
Rocky intertidal community food web (Paine’s 1966 study)
• (Producer level omitted from original figure)• Level 1
– herbivorous gastropods and chitons– filter feeding bivalves– suspension feeding barnacles and
brachiopods
• Levels 2-4: carnivorous gastropods• Level 5: top carnivore
– Heliaster starfish
![Page 73: Species diversity](https://reader034.vdocuments.net/reader034/viewer/2022051215/56814c24550346895db928aa/html5/thumbnails/73.jpg)
73
Keystone species
• Usually the top carnivore
• Presence or absence determines community structure and composition
![Page 74: Species diversity](https://reader034.vdocuments.net/reader034/viewer/2022051215/56814c24550346895db928aa/html5/thumbnails/74.jpg)
74
Food web of a rocky intertidal community, northern Gulf of California (after Paine 1966).
Producers Producers Producers Producers
Top carnivore
![Page 75: Species diversity](https://reader034.vdocuments.net/reader034/viewer/2022051215/56814c24550346895db928aa/html5/thumbnails/75.jpg)
75
Food web of a rocky intertidal community, northern Gulf of California (after Paine 1966).
Producers Producers Producers Producers
Top carnivore
X XX
X
X
XSpecies outcompeted in absence of
keystone species
Space competitor
![Page 76: Species diversity](https://reader034.vdocuments.net/reader034/viewer/2022051215/56814c24550346895db928aa/html5/thumbnails/76.jpg)
76
Keystone species
• Paine (1974): Pacific rocky intertidal community– dominated by Pisaster starfish– remove starfish → mussel Mytilus californiensis
↑ → excludes all other invertebrate species– Mytilus becomes numerically dominant– Pisaster feeds on Mytilus → prevents Mytilus
domination of community → ↑ community diversity
![Page 77: Species diversity](https://reader034.vdocuments.net/reader034/viewer/2022051215/56814c24550346895db928aa/html5/thumbnails/77.jpg)
77
Figure 23.3, p. 462. Simplified Antarctic marine food web.
![Page 78: Species diversity](https://reader034.vdocuments.net/reader034/viewer/2022051215/56814c24550346895db928aa/html5/thumbnails/78.jpg)
78
Fig. 23.4, p. 464. Food web of boreal forest of northwest Canada.
![Page 79: Species diversity](https://reader034.vdocuments.net/reader034/viewer/2022051215/56814c24550346895db928aa/html5/thumbnails/79.jpg)
79
Generalizations about food webs
• Size of animal increases with increase in trophic level
• Abundance decreases with increase in trophic level
• Large animals can not exist on small animals as prey
• Small carnivores are limited to prey that can fit into their mouths
![Page 80: Species diversity](https://reader034.vdocuments.net/reader034/viewer/2022051215/56814c24550346895db928aa/html5/thumbnails/80.jpg)
80
Which trophic level is most important?
• Studies by Charles Elton in two square miles of Wytham Woods
• Which species could be removed without changing the community?– top carnivore, except keystone species– lower levels are food source for higher levels– importance of top carnivores <<< herbivores
![Page 81: Species diversity](https://reader034.vdocuments.net/reader034/viewer/2022051215/56814c24550346895db928aa/html5/thumbnails/81.jpg)
81
Which trophic level is most important?
• Dependent on complexity of community– increased number of interconnections in
community → increased complexity of food web → increased stability of community structure → alternate food sources should one be removed
– redundancy model versus rivet model
![Page 82: Species diversity](https://reader034.vdocuments.net/reader034/viewer/2022051215/56814c24550346895db928aa/html5/thumbnails/82.jpg)
82
Which trophic level is most important?
• Determining species importance– species with highest biomass– where nutrients accumulate– where energy accumulates