41 Species Interactions.

41 Species Interactions

Do now: First: work in your groups to go over HW
1. Define the following terms: Invasive species Niche Competition 2. Use the three words in a sentence.

Overview: Communities in Motion
A biological community is an assemblage of populations of various species living close enough for potential interaction For example, the “carrier crab” carries a sea urchin on its back for protection against predators 3

Figure 41.1 Figure 41.1 Which species benefits from this interaction? 4

1.Interpret the experiment:
What effect does Balanus have on the niche Of chthamalus? b) How does competition Impact an organisms niche? c) Is this an example of Interspecifc or intraspecific Competition?

Concept 41.1: Interactions within a community may help, harm, or have no effect on the species involved Ecologists call relationships between species in a community interspecific interactions Competition predation/ herbivory symbiosis (parasitism, mutualism, and commensalism), and facilitation Interspecific interactions can affect the survival and reproduction of species. 6

Competition Interspecific competition occurs when species compete for a resource that limits their growth or survival Example: american bullfrogs on native population 7

Competitive Exclusion
Strong competition can lead to competitive exclusion, local elimination of a competing species The competitive exclusion principle states that two species competing for the same limiting resources cannot coexist in the same place Which native species would be victim of competitive exclusion? What are some ways in which to reduce competition? 8

Ecological Niches and Natural Selection
Evolution is evident in the concept of the ecological niche, the specific set of biotic and abiotic resources used by an organism How might a niche reduce competition? 9

Resource partitioning is differentiation of ecological niches, enabling similar species to coexist in a community 10

A. distichus perches on fence posts and other sunny surfaces.
Figure 41.2 A. distichus perches on fence posts and other sunny surfaces. A. insolitus usually perches on shady branches. A. ricordii Figure 41.2 Resource partitioning among Dominican Republic lizards A. insolitus A. aliniger A. christophei A. distichus A. cybotes A. etheridgei 11

Figure 41.2a A. distichus Figure 41.2a Resource partitioning among Dominican Republic lizards (part 1: A. distichus) 12

Figure 41.2b A. insolitus Figure 41.2b Resource partitioning among Dominican Republic lizards (part 2: A. insolitus) 13

A species’ fundamental niche is the niche potentially occupied by that species
A species’ realized niche is the niche actually occupied by that species As a result of competition, a species’ fundamental niche may differ from its realized niche For example, the presence of one barnacle species limits the realized niche of another species 14

Experiment High tide Chthamalus Balanus Chthamalus realized niche
Figure 41.3 Experiment High tide Chthamalus Balanus Chthamalus realized niche Balanus realized niche Ocean Low tide Results High tide Figure 41.3 Inquiry: Can a species’ niche be influenced by interspecific competition? Ask: what happens to the brown barnacles Chthamalus fundamental niche Ocean Low tide 15

Character Displacement
Character displacement is a tendency for characteristics to be more divergent in sympatric populations of two species than in allopatric populations of the same two species Sympatric: geographically similar location Allopatric: geographically different location An example is variation in beak size between populations of two species of Galápagos finches 16

Santa María, San Cristóbal Sympatric populations 40
Figure 41.4 G. fuliginosa G. fortis Beak depth 60 Los Hermanos 40 G. fuliginosa, allopatric 20 60 Daphne Percentages of individuals in each size class 40 G. fortis, allopatric 20 Figure 41.4 Character displacement: indirect evidence of past competition 60 Santa María, San Cristóbal Sympatric populations 40 20 8 10 12 14 16 Beak depth (mm) 17

Do Now was the competition between the bull frog and native species interspecific competition or intraspecific competition? Explain Which frog was victim of competitive exclusion? Explain Red squirrels occupy coniferous and broad leaf woodland however with the gray squirrel they only occupy coniferous forest. Explain the red squirrel’s fundamental and realized niche.

What do the numbers 5,40,60,16 represent?
HW Questions? What do the numbers 5,40,60,16 represent? As those numbers increase what happens to the amount of time needed to under metamorphosis? Is this density independent or density dependent ?

Predation Predation (/− interaction) refers to an interaction in which one species, the predator, kills and eats the other, the prey Why is it that prey do not go extinct? 20

(a) Cryptic coloration Canyon tree frog Figure 41.5a
Figure 41.5a Examples of defensive coloration in animals (part 1: cryptic coloration) 21

(b) Aposematic coloration Poison dart frog Figure 41.5b
Figure 41.5b Examples of defensive coloration in animals (part 2: aposematic coloration) 22

(c) Batesian mimicry: A harmless species mimics a harmful one.
Figure 41.5c (c) Batesian mimicry: A harmless species mimics a harmful one. Nonvenomous hawkmoth larva Venomous green parrot snake Figure 41.5c Examples of defensive coloration in animals (part 3: Batesian mimicry) 23

(d) Müllerian mimicry: Two unpalatable species mimic each other.
Figure 41.5d (d) Müllerian mimicry: Two unpalatable species mimic each other. Cuckoo bee Yellow jacket Figure 41.5d Examples of defensive coloration in animals (part 4: Müllerian mimicry) 24

Animals with effective chemical defenses often exhibit bright warning coloration, called aposematic coloration Predators are particularly cautious in dealing with prey that display such coloration 25

Prey display various defensive adaptations
Behavioral defenses include hiding, fleeing, forming herds or schools, and active self-defense Animals also have morphological and physiological defense adaptations Cryptic coloration, or camouflage, makes prey difficult to spot Video: Sea Horses 26

(c) Batesian mimicry: A harmless species mimics a harmful one.
Figure 41.5 (a) Cryptic coloration (b) Aposematic coloration Canyon tree frog Poison dart frog (c) Batesian mimicry: A harmless species mimics a harmful one. Nonvenomous hawkmoth larva (d) Müllerian mimicry: Two unpalatable species mimic each other. Venomous green parrot snake Cuckoo bee Yellow jacket Figure 41.5 Examples of defensive coloration in animals 27

In some cases, a prey species may gain significant protection by mimicking the appearance of another species In Batesian mimicry, a palatable or harmless species mimics an unpalatable or harmful model 28

In Müllerian mimicry, two or more unpalatable species resemble each other
29

Herbivory Herbivory (/− interaction) refers to an interaction in which an herbivore eats parts of a plant or alga In addition to behavioral adaptations, some herbivores may have chemical sensors or specialized teeth or digestive systems Plant defenses include chemical toxins and protective structures 30

Figure 41.6 Figure 41.6 A marine herbivore 31

Symbiosis Symbiosis is a relationship where two or more species live in direct and intimate contact with one another 32

Parasitism In parasitism (/− interaction), one organism, the parasite, derives nourishment from another organism, its host, which is harmed in the process Parasites that live within the body of their host are called endoparasites Parasites that live on the external surface of a host are ectoparasites 33

Many parasites have a complex life cycle involving multiple hosts
Some parasites change the behavior of the host in a way that increases the parasites’ fitness Parasites can significantly affect survival, reproduction, and density of host populations 34

Mutualism Mutualistic symbiosis, or mutualism (/ interaction), is an interspecific interaction that benefits both species In some mutualisms, one species cannot survive without the other In other mutualisms, both species can survive alone Mutualisms sometimes involve coevolution of related adaptations in both species Video: Clownfish and Anemone 35

(a) Ants (genus Pseudomyrmex) in acacia tree
Figure 41.7 Figure 41.7 Mutualism between acacia trees and ants (a) Ants (genus Pseudomyrmex) in acacia tree (b) Area cleared by ants around an acacia tree 36

(a) Ants (genus Pseudomyrmex) in acacia tree
Figure 41.7a Figure 41.7a Mutualism between acacia trees and ants (part 1: ants) (a) Ants (genus Pseudomyrmex) in acacia tree 37

(b) Area cleared by ants around an acacia tree
Figure 41.7b Figure 41.7b Mutualism between acacia trees and ants (part 2: acacia tree) (b) Area cleared by ants around an acacia tree 38

Commensalism In commensalism (/0 interaction), one species benefits and the other is neither harmed nor helped Commensal interactions are hard to document in nature because any close association likely affects both species 39

Figure 41.8 Figure 41.8 A possible example of commensalism between cattle egrets and African buffalo 40

Facilitation Facilitation (/ or 0/) is an interaction in which one species has positive effects on another species without direct and intimate contact For example, the black rush makes the soil more hospitable for other plant species 41

With Juncus Without Juncus
Figure 41.9 8 6 Number of plant species 4 2 Figure 41.9 Facilitation by black rush (Juncus gerardi) in New England salt marshes (a) Salt marsh with Juncus (foreground) With Juncus Without Juncus (b) 42

(a) Salt marsh with Juncus (foreground)
Figure 41.9a Figure 41.9a Facilitation by black rush (Juncus gerardi) in New England salt marshes (photo) (a) Salt marsh with Juncus (foreground) 43

Concept 41.2: Diversity and trophic structure characterize biological communities
Two fundamental features of community structure are species diversity and feeding relationships Sometimes a few species in a community exert strong control on that community’s structure 44

Species Diversity Species diversity of a community is the variety of organisms that make up the community It has two components: species richness and relative abundance Species richness is the number of different species in the community Relative abundance is the proportion each species represents of all individuals in the community 45

A B C D Community 1 Community 2 A: 25% B: 25% C: 25% D: 25% A: 80%
Figure 41.10 A B C D Community 1 Community 2 Figure Which forest is more diverse? A: 25% B: 25% C: 25% D: 25% A: 80% B: 5% C: 5% D: 10% 46

Diversity and Community Stability
Ecologists manipulate diversity in experimental communities to study the potential benefits of diversity For example, plant diversity has been manipulated at Cedar Creek Natural History Area in Minnesota for two decades 47

Figure 41.12 Figure Study plots at the Cedar Creek Natural History Area, site of long-term experiments in which researchers have manipulated plant diversity 48

Communities with higher diversity are
More productive and more stable in their productivity Able to produce biomass (the total mass of all individuals in a population) more consistently than single species plots Better able to withstand and recover from environmental stresses More resistant to invasive species, organisms that become established outside their native range 49

Trophic Structure Trophic structure is the feeding relationships between organisms in a community It is a key factor in community dynamics Food chains link trophic levels from producers to top carnivores 50

Quaternary consumers: carnivores
Figure 41.13 Quaternary consumers: carnivores Tertiary consumers: carnivores Secondary consumers: carnivores Figure Examples of terrestrial and marine food chains Primary consumers: herbivores and zooplankton Primary producers: plants and phytoplankton 51

A food web is a branching food chain with complex trophic interactions
Species may play a role at more than one trophic level Video: Shark Eating a Seal 52

Humans Smaller toothed whales Baleen whales Sperm whales Elephant
Figure 41.14 Humans Smaller toothed whales Baleen whales Sperm whales Elephant seals Crab- eater seals Leopard seals Birds Fishes Squids Figure An Antarctic marine food web Carnivorous plankton Copepods Krill Phyto- plankton 53

Species with a Large Impact
Certain species have a very large impact on community structure Such species are highly abundant or play a pivotal role in community dynamics 54

Dominant species are those that are most abundant or have the highest biomass
One hypothesis suggests that dominant species are most competitive in exploiting resources Another hypothesis is that they are most successful at avoiding predators and disease 55

Keystone species exert strong control on a community by their ecological roles, or niches
In contrast to dominant species, they are not necessarily abundant in a community Field studies of sea stars illustrate their role as a keystone species in intertidal communities 56

Number of species present
Figure 41.15 Experiment Results 20 15 With Pisaster (control) Number of species present Figure Inquiry: Is Pisaster ochraceus a keystone predator? 10 Without Pisaster (experimental) 5 1963’64 ’65 ’66 ’67 ’68 ’69 ’70 ’71 ’72 ’73 Year 57

Ecosystem engineers (or “foundation species”) cause physical changes in the environment that affect community structure For example, beaver dams can transform landscapes on a very large scale 58

Figure 41.16 Figure Beavers as ecosystem engineers 59

Bottom-Up and Top-Down Controls
The bottom-up model of community organization proposes a unidirectional influence from lower to higher trophic levels In this case, the presence or absence of mineral nutrients determines community structure, including the abundance of primary producers 60

The bottom-up model can be represented by the equation
where N  mineral nutrients V  plants H  herbivores P  predators N V H P 61

The top-down model, also called the trophic cascade model, proposes that control comes from the trophic level above In this case, predators control herbivores, which in turn control primary producers N V H P 62

Biomanipulation is used to improve water quality in polluted lakes
In a Finnish lake, blooms of cyanobacteria (primary producers) occurred when zooplankton (primary consumers) were eaten by large populations of roach fish (secondary consumers) Removal of roach fish and addition of pike perch (tertiary consumers) controlled roach populations, allowing zooplankton populations to increase and ending cyanobacterial blooms 63

Polluted State Restored State Fish Abundant Rare Zooplankton Rare
Figure 41.UN02 Polluted State Restored State Fish Abundant Rare Zooplankton Rare Abundant Figure 41.UN02 In-text figure, biomanipulation, p. 855 Algae Abundant Rare 64

Concept 41.3: Disturbance influences species diversity and composition
Decades ago, most ecologists favored the view that communities are in a state of equilibrium This view was supported by F. E. Clements, who suggested that species in a climax community function as an integrated unit 65

Other ecologists, including A. G. Tansley and H. A
Other ecologists, including A. G. Tansley and H. A. Gleason, challenged whether communities were at equilibrium Recent evidence of change has led to a nonequilibrium model, which describes communities as constantly changing after being buffeted by disturbances A disturbance is an event that changes a community, removes organisms from it, and alters resource availability 66

Characterizing Disturbance
Fire is a significant disturbance in most terrestrial ecosystems A high level of disturbance is the result of a high intensity and high frequency of disturbance Low disturbance levels result from either low intensity or low frequency of disturbance 67

High levels of disturbance exclude many slow-growing species
The intermediate disturbance hypothesis suggests that moderate levels of disturbance can foster greater diversity than either high or low levels of disturbance High levels of disturbance exclude many slow-growing species Low levels of disturbance allow dominant species to exclude less competitive species 68

In a New Zealand study, the richness of invertebrate taxa was highest in streams with an intermediate intensity of flooding 69

Index of disturbance intensity (log scale)
Figure 41.17 35 30 25 Number of taxa 20 15 Figure Testing the intermediate disturbance hypothesis 10 0.9 1.0 1.1 1.2 1.3 1.4 1.5 1.6 1.7 1.8 1.9 2.0 Index of disturbance intensity (log scale) 70

The Yellowstone forest is an example of a nonequilibrium community
The large-scale fire in Yellowstone National Park in 1988 demonstrated that communities can often respond very rapidly to a massive disturbance The Yellowstone forest is an example of a nonequilibrium community 71

Do now: Identify the photic and aphotic zones of the lake Distinguish between eutrophic and oligotrophic lakes What biological phenomenon is occurring below?

Littoral zone Limnetic zone Photic zone Pelagic Benthic zone zone
Figure 40.11 Littoral zone Limnetic zone Photic zone Pelagic zone Benthic zone Aphotic zone Figure Zonation in a lake Zonation in a lake 73

Ecological Succession
Ecological succession is the sequence of community and ecosystem changes after a disturbance Primary succession occurs where no soil exists when succession begins Secondary succession begins in an area where soil remains after a disturbance 74

Early-arriving species and later-arriving species may be linked in one of three processes
Early arrivals may facilitate the appearance of later species by making the environment favorable Early species may inhibit the establishment of later species Later species may tolerate conditions created by early species, but are neither helped nor hindered by them 75

Retreating glaciers provide a valuable field research opportunity for observing succession
Succession on the moraines in Glacier Bay, Alaska, follows a predictable pattern of change in vegetation and soil characteristics The exposed moraine is colonized by pioneering plants, including liverworts, mosses, fireweed, Dryas, and willows 76

Glacier Bay Alaska 0 5 10 15 Kilometers Figure 41.19-1
Figure Glacial retreat and primary succession at Glacier Bay, Alaska (step 1) Kilometers 77

1941 1 Pioneer stage Glacier Bay Alaska 0 5 10 15 Kilometers
Figure 1941 1 Pioneer stage Glacier Bay Alaska Figure Glacial retreat and primary succession at Glacier Bay, Alaska (step 2) Kilometers 78

1941 1907 1 Pioneer stage 2 Dryas stage Glacier Bay Alaska 0 5 10 15
Figure 1941 1907 1 Pioneer stage 2 Dryas stage Glacier Bay Alaska Figure Glacial retreat and primary succession at Glacier Bay, Alaska (step 3) Kilometers 79

1941 1907 1 Pioneer stage 1860 2 Dryas stage Glacier Bay Alaska 3
Figure 1941 1907 1 Pioneer stage 1860 2 Dryas stage Glacier Bay Alaska Figure Glacial retreat and primary succession at Glacier Bay, Alaska (step 4) Kilometers 3 Alder stage 80

1941 1907 1 Pioneer stage 1860 2 Dryas stage Glacier Bay Alaska 1760 4
Figure 1941 1907 1 Pioneer stage 1860 2 Dryas stage Glacier Bay Alaska Figure Glacial retreat and primary succession at Glacier Bay, Alaska (step 5) 1760 Kilometers 4 Spruce stage 3 Alder stage 81

Figure 41.19a Figure 41.19a Glacial retreat and primary succession at Glacier Bay, Alaska (part 1: pioneer) 1 Pioneer stage 82

After about three decades, Dryas dominates the plant community
83

Figure 41.19b Figure 41.19b Glacial retreat and primary succession at Glacier Bay, Alaska (part 2: Dryas) 2 Dryas stage 84

A few decades later, alder invades and forms dense thickets
85

Figure 41.19c Figure 41.19c Glacial retreat and primary succession at Glacier Bay, Alaska (part 3: alder) 3 Alder stage 86

In the next two centuries, alder are overgrown by Sitka spruce, western hemlock, and mountain hemlock 87

Figure 41.19d Figure 41.19d Glacial retreat and primary succession at Glacier Bay, Alaska (part 4: spruce) 4 Spruce stage 88

Succession is the result of changes induced by the vegetation itself
On the glacial moraines, vegetation increases soil nitrogen content, facilitating colonization by later plant species 89

Human Disturbance Humans have the greatest impact on biological communities worldwide Human disturbance to communities usually reduces species diversity Trawling is a major human disturbance in marine ecosystems 90

Figure 41.20 Figure Disturbance of the ocean floor by trawling 91

Figure 41.20a Figure 41.20a Disturbance of the ocean floor by trawling (part 1: before) 92

Figure 41.20b Figure 41.20b Disturbance of the ocean floor by trawling (part 2: after) 93

Concept 41.4: Biogeographic factors affect community diversity
Latitude and area are two key factors that affect a community’s species diversity 94

Latitudinal Gradients
Species richness is especially great in the tropics and generally declines along an equatorial-polar gradient Two key factors in equatorial-polar gradients of species richness are probably evolutionary history and climate 95

Temperate and polar communities have started over repeatedly following glaciations
The greater age of tropical environments may account for their greater species richness In the tropics, the growing season is longer, so biological time runs faster 96

Climate is likely the primary cause of the latitudinal gradient in biodiversity
Two main climatic factors correlated with biodiversity are sunlight and precipitation They can be considered together by measuring a community’s rate of evapotranspiration Evapotranspiration is evaporation of water from soil plus transpiration of water from plants 97

Vertebrate species richness
Figure 41.21 200 100 Vertebrate species richness (log scale) 50 Figure Energy, water, and species richness 10 500 1,000 1,500 2,000 Potential evapotranspiration (mm/yr) 98

Area Effects The species-area curve quantifies the idea that, all other factors being equal, a larger geographic area has more species 99

Species richness on islands depends on island size, distance from the mainland, immigration, and extinction The equilibrium model of island biogeography maintains that species richness on an ecological island levels off at a dynamic equilibrium point 100

Studies of species richness on the Galápagos Islands support the prediction that species richness increases with island size 101

Area of island (hectares)
Figure 41.22 Results 400 200 100 Number of plant species (log scale) 50 25 10 Figure Inquiry: How does species richness relate to area? 5 10 100 103 104 105 106 Area of island (hectares) (log scale) 102

Figure 41.UN03 Figure 41.UN03 Summary of key concepts: species interactions 103

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