Day 8 Objective: Describe the more difficult
community concepts like disturbance, succession and
island biogeography. The good news is this is really just
common sense. Chapter 53.
Overview:
An ecosystem is a complete community of interdependent organisms as
well as the inorganic components of their environment; by contrast, a
biological community is just the living members of an ecosystem. Within
the study of biological communities there are a great number of
complexities involved in analyzing the relationships between species as
well as the characteristics of specific communities. Yet many of the
concepts applicable to biological communities as a whole also apply to
human communities in particular, and this makes these ideas easier to
understand. For example, the competitive urge that motivates humans to
war (and to less destructive forms of strife in the business or sports
worlds) may be linked to the larger phenomenon of biological competition.
Indeed, much of the driving force behind the development of human
societies, as it turns out, has been biological in nature.
A group of interdependent organisms living and interacting with each
other in the same habitat.
Useful Diagrams/Helpful Documents:
http://www.sjsu.edu/depts/EnvStudies/syllabi/fall08/envs10/L14_Dis
turbance.pdf
https://docs.google.com/viewer?a=v&q=cache:qtn2vzoeP0J:www.science.marshall.edu/may/bsc320-17biodiversity.ppt+&hl=en&gl=us&pid=bl&srcid=ADGEESjBQ6GT40Q5
vzMYhm78oyXmvVU3FwXrSbNWi8D3TA1csHLgFEpypwIhxSiOBMN3bMDIY1WfdKjHi17dULH7qqadYs_xzZA2wZIPCmlJN1PmReiY
RypZ3zzBuVz1NdQLEoDhMf&sig=AHIEtbSciNMxyFWkKDBN4pyjPkCc7lZ3Q
https://docs.google.com/viewer?a=v&q=cache:fgvrA_zwZZcJ:www
.eve.ucdavis.edu/catoft/eve101/Protected/PPT/Lec10_community_
III.ppt+&hl=en&gl=us&pid=bl&srcid=ADGEESjpvug5DGQSY0aMCxe
D1ulDhEWvxOpzGJ61HKuqeDutNKDT5CYBEgn0kMQyQGV2tfdy
JUPUo-Js3L2EvyGyKi4Z8osLmFv6w4LDA57XlfKD2g6JSQ1mHylxsiwBCU5zcEcX8f&sig=AHIEtbQNzOnneR6TdRQwv0bkhDkA7_lsmw
http://quizlet.com/3647765/22-community-succession-flash-cards/
http://www.montana.edu/wwwbi/staff/creel/bio303/Succession.pdf
YouTube Informational Videos:
http://www.youtube.com/results?search_query=island+biogeograph
y&oq=island+bio&aq=0&aqi=g1g-m2&aql=&gs_nf=1&gs_l=youtubepsuggest.3.0.0j0i5l2.41208.43811.0.45795.10.10.0.1.1.0.78.505.9.9.0.
http://www.youtube.com/watch?v=Dw0KLktiKGI
Questions:
1. Why does colonization rate decline as S increases, according to the
Theory of Island Biogeography? Why does extinction rate increase
with S?
2. Demonstrate, by graphing “rate of colonization and extinction” against
“species richness”, why small islands are expected to have lower
equilibrium levels of diversity than large islands. Explain in words
what the mechanism is for reduced diversity.
3. Explain how island biogeography theory can be applied to conservation
biology.
4. Suppose you are planning to study the bird communities on the islands
shown in this figure. Islands A and B lie equal distances from the
mainland but differ in area, while islands B and C are identical in area
but lie at different distances from the mainland. According to the
equilibrium model of island biogeography, which of the islands should
experience higher rates of immigration? Explain your prediction.
5. How does diversity vary with the frequency of disturbance?
Answers:
1. Colonization rate declines because colonization is defined as the
arrival of a new species. As species accumulate, it becomes increasingly
likely that any new arrivals are already present, and thus don’t count as
new colonization. Extinction increases as S increases because of the
greater likelihood of competitive exclusion. An additional factor is that
as S increases, the population size of each individual species is likely to
go down, and smaller populations are more vulnerable to extinction from
a variety of factors (disturbance, disease, etc).
2.It proposes that large islands will experience lower extinction rates,
because population sizes are larger and competitive exclusion is less
likely; the equilibrium level of species diversity is therefore higher.
Colonization
rate
Extinction
rate
S
3. Island biogeography theory also led to the development of habitat
corridors as a conservation tool to increase connectivity between habitat
islands. Habitat corridors can increase the movement of species between
parks and reserves and therefore increase the number of species that
can be supported, but they can also allow for the spread of disease and
pathogens between populations, complicating the simple proscription of
connectivity being good for biodiversity.
4. According to the equilibrium model the island closer to mainland
should experience more immigration because they are closer and it is
easier for species to move from the island to the mainland.
5. Things are more diverse if the frequency of disturbance is higher.
Vocabulary
Autotroph: An organism that can synthesize its own food.
Primary producer: Synonym for autotroph
Net primary productivity: Products of photosynthesis that are invested
in production of new tissue
Consumer: Organisms that gain energy by eating other organisms
(contrast with autotroph)
Indirect interactions: Interactions between two species that are
mediated by additional species (contrast with direct interactions)
Direct interactions: Interactions between two species that have actual
contact with each other—that interact in a pairwise fashion as
competitors, predator-prey, or mutualists.
Food web: Describes how a community is organized according to feeding
relationships—diagrams which organisms eat which. “A complete
description of the trophic relationships among the organisms in an
ecosystem” (Freeman, pg 1248)
Trophic level: An organism’s energy source—organisms that acquire
energy from the same type of source occupy the same trophic level.
Examples of trophic levels include: primary producers, primary
consumers, secondary consumers.
Bottom-up control: Abundance of organisms is controlled by food
availability (i.e., by the abundance at a lower trophic level).
Top-down control: Abundance of organisms is controlled by consumption
by predators/herbivores at higher trophic levels.
Trophic Cascades Hypothesis: Describes pattern of alternating top-down
and bottom-up control in ecosytems; begins with bottom-up control
at the uppermost trophic level.
Keystone species: : A species, usually (but not always) from an upper
trophic level, whose influence on a community is disproportionate to
its abundance, and whose presence is instrumental in maintaining
community composition.
Disturbance: An event, discrete in time, that kills individuals and/or
removes biomass and thus opens up opportunities for new individuals
to colonize a site.
Disturbance regime: A description of what types of disturbance are
important, how often they occur, and their severity.
Succession: Process of community recovery following disturbance
Primary succession: succession following a disturbance that removes
both biota and soils.
Secondary succession: succession following a disturbance that removes
biota, but leaves soils more or less intact.
Facilitation: presence of a species has a positive effect on another. Not
necessarily a mutualism—in most cases the facilitation benefits one
species but harms the other!
Inhibition: Inhibition occurs when a species has a negative affect on the
growth rate or survival or another. Similar to competition, but there
is an implied asymmetry that means that inhibition can actually be
closer to an amensalism—the species that does the inhibiting may be
totally unaffected by the interaction.
Species richness:. The number of species present in a community