Transcript Ecological niche

CHAPTER 53 –
COMMUNITY ECOLOGY
Themes:
•Interaction with the environment
•Regulation
•Scientific Inquiry
•Evolution
Objectives:
Rivet vs. Redundancy Models
Populations are linked by competition, predation, mutualism,
and commensalism
Trophic structure is key in community dynamics
Dominant and keystone species exert strong controls on a
community
Bottom-up (nutrients) vs. Top-down (predation)
Most communities are in a state of nonequilibrium due to
disturbances (Humans the typical agent)
Species Richness – related to communities geographic size
Community biodiversity – measures the # of species and
their relative abundance
Root Words
Crypto –
Ecto –
Endo –
Herb –
- vora
Hetero –
Inter –
Mutu –
Community – all organisms that live in a particular area; many
populations (different species) living close enough to have potential
interaction.
Coevolution – Reciprocal evolutionary adaptations in 2 species.
(1) Example: Flowers and their pollinators (insects, birds).
(a) Change in one species – new selective force for
another species
Cryptic Coloration (camouflage); 3 types of mimicry; aposematic
(Warning) coloration
Deception coloration
Camouflage
(E) Species richness- the number of species that a community contains.
1). This increases as you travel north from the South pole.
(F) All of the following act to increase species diversity:
1). Keystone predators; patchy environments; moderate
disturbances and migration of a population.
(G) Herbivory – The consumption of plant material by a herbivore.
(H) Creatures can defend themselves by such things as cryptic coloration;
mobbing; hiding or fleeing.
Community Models
Redundancy Model – Most of the species in a community are not
tightly associated with each other, and the web of life is very loose.
Thus, the increase or decrease of ones species in the community has
little effect on the other species.
1. Example: If one predator disappears and then another
predatory species will usually take its place.
Rivet Model – that says that most species in a community are
associated tightly with other species in a web. Thus increasing or
decreasing one species in a community affects many other species.
Mimicry Systems depend on Defensive
Behavior:
a. The model is noxious or disagreeable, and easily
recognized.
b. The mimic is less common than their models.
c. The ability of prey to “learn” characteristics of their predator.
Mullerian mimicry – is when 2 dangerous organisms resemble each
other. (like 2 poisonous snakes that resemble each other).
Ecologists consider STABILITY to be a measure of the ability of a
community to either resist change or to recover its original state after
change.
Trophic structure of a community describes the feeding relationships
within a community.
Many plant species in communities seem to independently distributed.
(I.) Niche
1). Ecological niche – sum total of an organism’s use of biotic
and abiotic resources in the environment.
2). Fundamental niche – resources a population theoretically
is capable of using under ideal conditions.
(a) Physiological limits of tolerance.
(b) Absence of interaction with other organisms.
3). Realized Niche – Portion of the fundamental niche the
organism actually uses.
*(NOTE): Competition between species makes the difference
between # 2 & 3.*
4). Need to know definitions and comparisons: parasitism,
commensalism and mutualism
Fig. 53.3 – Resource Partitioning in a group of sympatric
lizards
Slight variations in a
niche allow closely
related species to
coexist.
4 ?’s. on Fig. 50.4 Biogeographical Realms
(J) Competitive Exclusion Principle – 2 species cannot coexist in a
community if their ecological niches are identical.
Competition in Laboratory Populations of
Paramecium.
This is especially
true if one species
has a reproductive
advantage over
the other.
(K) Keystone Predator – exerts an important regulating effect on
other species in a community.
(1) Helps maintain higher species diversity (reduces strong
competitors).
(L) Species Equitability – The relative number of individuals in
each species.
Ecological Succession
Ecological Succession – Transition in species competition over time.
(Yellowstone Fires – did not take long for vegetation to return)
(A) Primary – no soil to forest ecosystem.
(B) Secondary – Existing community cleared by some disturbance
(fire etc.) Happens if soil is still intact.
(C ) Climax Community – last stage of succession (usually does
not happen due to disturbance in a ecosystem). There may not be
such a thing since most stable communities do not reach a stable
climax diversity. Disturbances are ongoing in ecosystems.
(D). This is due to continued disturbances in ecosystems.
E. Organisms sometimes induce succession 1 of 2 ways:
1. Inhibition – Early species prevent rather than assist
colonization by other species.
2. Facilitation – One species actually “paves the way” for another
species making the ecosystyem more favorable for the 2nd species.
Biogeography
Study of past and present distribution of species. (All Flora &
Fauna).
1. Island Biogeography – 5 ?’s (2 factors that determine the
rate at which new species eventually inhabit an island.)
(a). Rate of immigration.
(b). Rate of extinction of species on the island.
(c). Major Features of Island Biogeography
1). If several islands are close together to the mainland,
the largest island will have the greatest # of species & the lowest
extinction rate.
2). Usually the smallest most distant island from the
mainland will have the least # of species & lowest immigration
rate.
Humans have caused the greatest disturbance and thus the greatest
impact on ecosystems.
Sympatric – Reproductively isolated subpopulation in the midst of
its parent population.
1. Resource partitioning would most likely occur in sympatric
populations of species with a similar ecological niche.