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Lecture 16

Biology 2483A Lecture 16: Bio 2483 Lecture 16


Department
Biology
Course Code
BIOL 2483A
Professor
Sheila Macfie
Lecture
16

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Bio 2483 Lecture 16 change in communities
Key concepts
1. Agents of change act on communities across all temporal and spatial scales
2. Succession is the process of change in species composition over time as a
result of abiotic and biotic agents of change
3. Communities can follow different successional paths and display alternative
states
1. Agents of change act on communities across all temporal and spatial scales
12000 we were under glaciers
climate change rate of change is faster
fire or volcano erupting very fast rate of change
A) Agents of change can be abiotic or biotic
o i) Abiotic agents of change
arrow - time it took agent of change to change
E.g., communities were wiped out up to 23km away in 10 min
small duration of active change, but impact is long-term
scale
o ii) Biotic agents of change
e.g., burrowing by gopher
impact could be localized if a few gophers, but if a colony
the impact can be very big
intensity of agent of change isn’t proportional to amount of change
it causes
o iii) Interactions among abiotic and biotic agents
arrows are trophic energy
abiotic stress environment drought
in winter, ample water, 4 levels of trophic change
midges outcompete the insect larvae
Winter drought
Midges are drought sensitive so will be less of them, so larvae have less
competition
So larvae get more energy
Overall there’s less energy in the system causes big change in community bc
only 2 trophic levels are supported: primary producers and primary consumers)

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o Two categories of abiotic and biotic agents
Disturbance: event that directly physically injures or kills some individuals and creates
opportunities for other individuals
direct impact on what’s being affected
o abiotic > fire, avalanche
o biotic > grazing, trampling, logging
Stress: factor that reduces the rate of an important physiological process, thereby
reducing growth, reproduction or survival or some individuals
Stressors act on physiological processes
induces an indirect effect
abiotic: drought, freezing, pollution
biotic: disease, parasites
is it still a stress if there’s an adaptation? not rly no bc needs physiological
impact
B) Agents of change vary in their intensity, frequency, and extent
o Intensity (severity): proportional to amount of damage/death caused
o Frequency: measure of how often the agent of change has an effect
o Extent: proportional to the area of land or number of individuals
affected
o merged intensity & extent on the y axis
o circles = amount of change that agent caused
big circle, big change in community
o if low freq and low intensity, chance to recover is good
o if low freq and high intensity,
o if high freq and low intensity,
o if high freq and high intensity (upper right hand corner) place where
nothing can live
2. Succession: process of change in species composition over time as a result of abiotic & biotic agents of change
change in diversity richness & _________
eventually truck will corrode and degrade
natural for communities to change but the rate of change can be diff (fast or slow)
Succession involves a series of colonizations and extinctions, driven by agents of change
o get succession of new plant species that will support a new succession of animal species

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Forensic entomology
o Forensics can take advantage of this natural succession
o E.g., arthropods
o flies show up first to colonize, then taken over by beetles
o within each insect, forensics can narrow down the time
frame since we know their lifecycles and life stages
o knows exactly when corpse was there in min/days/years
etc. ago
Succession is unidirectional (simpler t more complex communities)
o Disturbance and stress send the community back to an earlier stage
o climax stage: life will go to particular defined stable community
A)
o starts w no life
o pioneer species come
o start to mineralize material
o organic matter builds up and other species can live there
o increased depth of soil over time
o over 100s of years for it to undergo succession to a mature community
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