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(Upload on August 10 2015) [ 日本語 | English ]

Island biogeography (島の生物地理学)






Mount Usu / Sarobetsu post-mined peatland
From left: Crater basin in 1986 and 2006. Cottongrass / Daylily

islands Fig. 1. "Real islands" and "habitat islands". Those kinds of islands can be analyzed by the identical numerical theory. (Wilson & Bossert 1971)

island biogeography, biogeogrpahy
索引
SLOSS, network
conservation (保全)
landscape (景観)
species-area curve (種数面積曲線)
(Simberloff 1974)

Equilibrium of species richness (種数平衡)


Concept
Fig. Four equilibrium points on number of species with diferent island sizes (small and large) and distance from mainland.(close and far). See also the table, shown below.

Alternative model of the evolutionary species equilibrium
island
E: diversity-dependent extinction curve
E’: diversity-dependent extinction curve

Each N is diversity on equilibrium stage

The rate of change in diversity
N(t): rate of change in diversity
δN/δt = S - E

S: equation 1, E: equilibrium
E = bN, b: constant for all N and for all t

α = a/Nmax δN/δt = [α - aN - b]N = [a(1 - N/Nmax) - b]N
Equilibrium value, δN/δt = 0 → N* = (1 - b/a)Nmax

(Walker & Valentine 1984)

Island sizeLargeSmall
Distance from mainlandCloseFarCloseFar
Immigraiton rate (移入率)HighLowHighLow
Extinction rate (絶滅率)HighHighLowLow
Equilibrium points of species (平衡点), s*DCBA

Single large or several small (SLOSS)


  1. To conserve specific animal and plant species
  2. To conserve many species

→ Which and how do we choose?

Reserve design and selection

→ Where do we reserve?

1. Several, large reservations
2. Many, small reservations

Island biogeography + scale
Zero-sum dynamics

Networks (ネットワーク)


Ecological network (ecosystem netowrk)

Corridors and flows

conduits: plants and animals are the primary flows along corridors
barrier or filter effects: e.g., erosion

Corridors (回廊)

long narrow patches, contrasts with surroundings, often disturbed, migration filters, often interrupted, different microclimate

Hedgerow function (生垣効果)

fence effect, hedgerow as conduits, hedgerow networks and flows

Ex. windbreak forest

Nodes and corridors

Function of nodes
  1. Intersection areas of corridors
  2. Sources or sinks (destinations) of flowing objects
Nodes occasionally control (a) amplify or speed up flows, (b) reduce "noise" or "irrelevancies" in flows, and (c) provide temporary storage, e.g., lake for migratory birds
Nodes often make loops, or alternative routes, such as railroad
Network connectivity
The degree to which all nodes in a system are linked by corridors

Complexity of networks
1. Gamma index, γ = L/Lmax = L/{3(V - 2)},

where L is the number of links, Lmax is the maximum possible number of links, and V is the number of nodes. Gamma index ranged from 0 (no link) to 1 (every node is linked to every other node)

2. Gravity model (重力分析)

Assumptions: interaction (= gravity, Tij) between centers(i, j) is:
a) directly proportional to mass (the scale of center) → mass(Pi, Pj), e.g., population, income, and gross proceeds
b) inversely proportional to the sum of squares of center → distance(dij), e.g., physical distance, traveling time

Tij = k(PiPj/dij²), k = constant

Dispute: doubtful if the models reflect regional coidentity in all the cases - imoportant to problem setting

Line                TTTTT..TTTTT, ....TT..... e.g., streams
Belt (strip)        TTTTTxx..xxTTTT           e.g., big rivers
Networks (quadrats) TTTTxx..xxTTTT
                    Txx..xxTTTTxx.
                    xx......TTxx..            e.g., grasslands
Background matrix and network

A landscape is composed of several types of landscape elements. Of these, the matrix is the most extensive and most connected landscape element type, and therefore, plays the dominant role in the functioning of the landscape (i.e., the flows of energy, materials, and species).

  1. absolute and relative area
  2. control over dynamics
  3. connectivity

Promotingg Ecological Network by Town Development
The Tokyo Garden Terrace Kioicho promotes Ecological Network in the middle of central Tokyo by connecting precious open spaces in the vicinity where a variety of wildlife has been identified. The entire green spaces are composed with multi-layered vegetation including various local species of plants to enhance conditions close to natural ecosystem. Also, a biotope on the site is to be integrated into an ecological network along with Shimizudani Park and Benkeibori Moat as well, and provides habitats of dragonflies and butterflies.

Kioi
Image Diagram of Ecological Network

紀尾井
Ecological Pyramid of Returning Wildlife
Ecological Pyramid:: a hierarchy of food chains with the principal predator at the top

November 24 2017

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