Transcript interspecific interactions

Chapter 41 Overview: Communities in Motion
 A biological community is populations of various
species living close enough for interaction
 For example, the “carrier crab” carries a sea urchin
on its back for protection against predators
© 2014 Pearson Education, Inc.
Concept 41.1: Interactions within a Community
 Ecologists call relationships between species in a
community interspecific interactions
 Interspecific interactions can affect the survival and
reproduction of each species. Effects can be
summarized as positive (), negative (−), or no
effect (0)
© 2014 Pearson Education, Inc.
Competition
 Interspecific competition (−/− interaction) occurs
when species compete for a resource that limits their
growth or survival
 Strong competition can lead to competitive
exclusion, local elimination of a competing species.
Two species competing for the same limiting
resources cannot coexist in the same place
© 2014 Pearson Education, Inc.
Ecological Niches and Natural Selection
 Ecological niche, the specific set of biotic and
abiotic resources used by an organism (it’s
ecological role)
 Resource partitioning is differentiation of ecological
niches, enabling similar species to
coexist in a community
© 2014 Pearson Education, Inc.
Figure 41.2
A. distichus perches on
fence posts and other
sunny surfaces.
A. insolitus usually
perches on shady
branches.
A. ricordii
A. insolitus
A. aliniger
A. distichus
A. christophei
A. cybotes
A. etheridgei
© 2014 Pearson Education, Inc.
Predation
 Predation (/− interaction) refers to an interaction in
which the predator kills and eats the prey
 Some feeding adaptations of predators are claws,
teeth, stingers, and poison
 Behavioral defenses of the prey include hiding,
fleeing, forming herds or schools, active selfdefense, camouflage, toxins
© 2014 Pearson Education, Inc.
Figure 41.5
(a) Cryptic
coloration
Canyon
tree frog
(b) Aposematic
coloration
Poison
dart frog
(c) Batesian mimicry: A harmless species mimics
a harmful one.
Nonvenomous
(d) Müllerian mimicry: Two unpalatable
hawkmoth larva
species mimic each other.
Venomous green
parrot snake
© 2014 Pearson Education, Inc.
Cuckoo bee
Yellow jacket
Herbivory
 Herbivory (/− interaction) refers 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
© 2014 Pearson Education, Inc.
Symbiosis is a relationship where two or more species live in
direct and intimate contact with one another.
3 General Types: Parasitism, Mutualism, Commensalism
Parasitism
 In parasitism (/− interaction) the parasite,
derives nourishment its host, which is harmed
 Some parasites change the behavior of the host in
a way that increases the parasites’ fitness
 Mind Control
of rodents!!
© 2014 Pearson Education, Inc.
Mutualism
 Mutualistic symbiosis, or mutualism (/ interaction),
benefits both species
 Mutualisms sometimes involve coevolution of related
adaptations in both species
(a) Ants (genus Pseudomyrmex) in
© 2014acacia
Pearson Education,
treeInc.
(b) Area cleared by ants around an
acacia tree
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
© 2014 Pearson Education, Inc.
Concept 41.2: Diversity and trophic structures
 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
 Species diversity depends on species richness and
abundance
A
B C
D
Community 1
A: Education,
25% Inc.
B: 25% C: 25% D: 25%
© 2014 Pearson
Community 2
A: 80% B: 5% C: 5% D: 10%
 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
© 2014 Pearson Education, Inc.
Trophic Structures
 Food chains link trophic levels from producers to
top carnivores
 A food web is a branching food chain with complex
trophic interactions
© 2014 Pearson Education, Inc.
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
 Dominant species are those that are most
abundant or have the highest biomass
 Keystone species exert strong control on a
community by their ecological roles, or niches
 In contrast to dominant species, keystone species
are not necessarily abundant in a community
© 2014 Pearson Education, Inc.
In western N. America the uncommon
sea star preys on mussels, which are
the dominant species and strong
competitor for space. Removing the
sea star caused species richness to
decline because the mussels
monopolized the rock and eliminated
most invertebrates and algae.
Number of species
present
Experiment Results
20
15
With Pisaster (control)
10
Without Pisaster (experimental)
5
0
1963’64 ’65 ’66 ’67 ’68 ’69 ’70 ’71 ’72 ’73
Year
© 2014 Pearson Education, Inc.
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.
 The bottom-up model can be represented by the
equation
N
V
H
P
where
N  mineral nutrients
V  plants
H  herbivores
P  predators
© 2014 Pearson Education, Inc.
 The top-down 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
 Scientist have used this approach to control algae
blooms by removing fish so there is more zooplankton
to eat the algae
© 2014 Pearson Education, Inc.
Concept 41.3: Disturbance influences species
diversity and composition
 Decades ago, most ecologists favored the view that
communities are in a state of equilibrium
 Recent evidence of change has led to a
nonequilibrium model, which describes
communities as constantly changing after
disturbances
 Describe some disturbances.
© 2014 Pearson Education, Inc.
 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
(a) Soon after fire
© 2014 Pearson Education, Inc.
(b) One year after fire
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
 Early arrivals may facilitate the appearance of later
species by making the environment favorable
 Early species may inhibit the establishment of later
species
© 2014 Pearson Education, Inc.
 Retreating glaciers provide a valuable field research
opportunity for observing succession
 Succession in Glacier Bay, Alaska, follows a
predictable pattern of change in vegetation and soil
characteristics
1. The exposed area is colonized by pioneering plants,
including liverworts, mosses, fireweed, Dryas, and
willows
2. After about three decades, Dryas dominates the plant
community
3. A few decades later, alder invades and forms dense
thicket.
4. In the next two centuries, alder are overgrown by Sitka
spruce, western hemlock, and mountain hemlock
© 2014 Pearson Education, Inc.
Figure 41.19-5
1941
1907
1 Pioneer stage
1860
Glacier
Bay
2 Dryas stage
Alaska
1760
4 Spruce stage
© 2014 Pearson Education, Inc.
0 5 10 15
Kilometers
3 Alder stage
Human Disturbance
 Humans have the greatest impact on biological
communities worldwide
 Human disturbance to communities usually reduces
species diversity
© 2014 Pearson Education, Inc.
Figure 41.23
© 2014 Pearson Education, Inc.