Next up…
You will examine how changes in the
landscape affect:
• (i) ecosystem diversity,
• (ii) species diversity,
• (iii) ecosystem function in terms of carbon
sequestration,
• (iv) population viability of a large herding
mammal,
• (v) foraging energetics of wide-ranging birds,
• (vi) genetic drift in a canopy tree.
You will generate three landscapes:
• (i) the original landscape,
• (ii) the landscape subjected to uncontrolled
fragmentation,
• (iii) the landscape subject to fragmentation
guided by some simple land use regulations
and alternatives.
Goal
• Contrast biological indicators in 3 landscapes
fragmented in different ways you will get a
good sense of:
– how fragmentation affects biodiversity
– how we can mitigate some of its negative effects
of human population growth and forest
conversion through
• Regulation
• Planning
• Incentives
Each grid square is
100m on a side
or 1 hectare
First scenario: Original landscape
• Scattered disturbances are typical : lightning strikes, fires,
or small, shifting garden plots
– 2% of the area and well dispersed.
• To mimic randomly choose 2% of the grid squares ( = 8)
– convert them to early successional vegetation (filled grid
squares)
– change the grid squares surrounding these to edge
environments (cross-hatched grid squares).
• What is the human population being supported within the
landscape?
– Each family (average of 5 people per family) needs exclusive
access to 3 hectares of cleared land for cultivation to meet their
needs or 50 hectares of forestland (upland or inundated and not
necessarily contiguous)
Second scenario: Uncontrolled
fragmentation
• New map
• Add a road bisecting the landscape (government initiative).
• The road width is negligible but it provides immediate access to the
grid squares traversed and those immediately adjacent to them
(150m back from the road). These are converted to agriculture.
• Convert adjacent forests to edge habitat (100m into a stand)
• Further settlement: add two more roads in perpendicular fashion
• Repeat the process of demarking converted lands 150m from the
roadsides and then the edge habitats adjacent to them.
• What is the human population being supported within the
landscape?
– Each family (average of 5 people per family) needs exclusive access to
3 hectares of cleared land for cultivation to meet their needs or 50
hectares of forestland (upland or inundated and not necessarily
contiguous)
Third scenario: Regulated
fragmentation with livelihood
alternatives
• New map
• Place roads anywhere you want to minimize fragmentation while
supporting the same number of people as in Scenario II and:
– Tripling the production rates on cultivated land through provision of
fertilizer and perhaps alternative crops so that local people now need
to clear only a third as much forest to meet their needs.
• In other words, each family can meet its needs on just one hectare of
cultivated land because productivity has been tripled.
• you only need to convert the lands up to 50m from roadsides, so fill in only the
blocks directly intersected by the road.
– Prohibit forest clearing of any habitat block that contains a
watercourse (roads can traverse watercourses but the forest blocks
that include watercourses are not cleared)
– Protect all rare ecosystems – no conversion of inundated forests!
• Need same
human
population
as scenario
II!
Next class…how to calculate:
• (i) ecosystem diversity,
• (ii) species diversity,
• (iii) ecosystem function in terms of carbon
sequestration,
• (iv) population viability of a large herding
mammal,
• (v) foraging energetics of wide-ranging birds,
• (vi) genetic drift in a canopy tree.
How to calculate:
• (i) ecosystem diversity,
• (ii) species diversity,
• (iii) ecosystem function in terms of carbon
sequestration,
• (iv) population viability of a large herding
mammal,
• (v) foraging energetics of wide-ranging birds,
• (vi) genetic drift in a canopy tree.
What is the human population being supported
within the landscape?
• Each family (average of 5 people per family) needs
exclusive access to 3 hectares of cleared land for
cultivation to meet their needs or 50 hectares of
forestland (upland or inundated and not necessarily
contiguous)
– Scenario I: ~45 people
– Scenario II: ~285 people
– Scenario III: ~255 people
Landscape analysis of ecosystem
diversity
Maximized where there is (1) more ecosystem types and
(2) an even representation of ecosystem types
Landscape-Level Carbon Sequestration
• Forest biomass averages 300 tons/ha
• Carbon comprises 50% of that.
• Forest clearing commits 95%of forest biomass to
carbon emissions
– 5% remains as relict living trees in pastures or inert as
charcoal in the soil.
• Forest edges lose 10% of their biomass because
mortality of trees is higher on the edges.
• Do not distinguish inundated forests from upland
forests for this exercise.
Faunal diversity
•
123 bird species:
– 31 use the matrix (converted lands)
– 92 use the forest edge
– 92 use forest interior.
•
62 frog species:
– 16 use the matrix,
– 52 use the forest interior
– 51 use the forest edge
•
Sum of the weights*values divided by sum of
the weights. In this case weights = extent of a
given ecosystem type and values = faunal
diversity for a particular type
15 mammal species:
– 4 use the matrix only
– 15 use the forest interior,
– 10 use the forest edge
•
Use a weighted average!
127 ant species
– 32 use the matrix only
– 104 use the primary forest
– 44 use the forest edge
For example, if the landscape was composed
of 1 000 grid squares, of which 500 were
primary forest, 250 were forest edge, and 250
were matrix, then ant diversity on average in
that landscape would equal:
•
123 bird species:
– 31 use the matrix (converted lands)
– 92 use the forest edge
– 92 use forest interior.
•
62 frog species:
– 16 use the matrix,
– 52 use the forest interior
– 51 use the forest edge
•
15 mammal species:
– 4 use the matrix only
– 15 use the forest interior,
– 10 use the forest edge
•
127 ant species
– 32 use the matrix only
– 104 use the primary forest
– 44 use the forest edge
Simple Population Viability of a
Herding Species with a Large HomeRange
Simple Population Viability of a Herding
Species with a Large Home-Range
• Assume
– > 1 km2 required to support a herd of white-lipped
peccaries at densities of five peccaries per km2
– peccaries are reluctant to cross roads and cleared areas
• Two questions:
– How many peccaries can each of the remaining forest
patches support?
– What fraction of patches contains both the upland and
wetland forest that are required to meet the annual needs
of these animals during the wet and dry seasons?
• Note that if at least one hectare of both wetland and upland forest
are not available within a forest patch, then a population cannot
be supported
Energetics of foraging
Energetics of foraging
• wide-ranging, large-bodied frugivorous bird
• must visit many sites every day to harvest newly ripened fruit.
• Assume
– the fruit tree species occurs only in inundated forests
– a pair of these birds must visit 5 such patches per day
• How far must these birds travel on average each day to meet their daily
needs in each scenario?
– trace the shortest path possible between all patches of inundated forest in the
landscape.
– Start with an isolated patch in one of the corners of the landscape.
– try to link all patches together as might a foraging bird that was trying to save energy
flying between all the patches.
– As you move sum up the distance of each sequential move.
– The total distance traveled divided by the total number of patches visited equals the
average cost of accessing a foraging site.
– Recall that the birds must visit 5 patches per day to meet their needs (X 5 above to meet
daily needs)
Genetic diversity
Pithecellobium
elegans
• “rare” tree species
• mature individuals distributed evenly through
the upland forest at a density of only one per
hectare.
• Any trees within 250m of any other trees
represent part of the same breeding
population
• Demarcate collections of individuals linked
through potential gene flow
• Need same
human
population
as scenario
II!
What is the least amount of genetic diversity lost by
any single population under each scenario over 100
generations?
• Amount of diversity lost is inversely
proportional to the size of the population.
• [1 - (1/(2*Ne))]t with t = 100
• Go with largest population in each scenario
Abstract
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The is one of the more “sprawling” exercises…
What is your objective?
What is your justification?
What is your general approach?
Critical findings?
General conclusion