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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)
[ biogeogrpahy ]
[ SLOSS ]
[ network ]
conservation (保全)
landscape (景観)
species-area curve (種数面積曲線)
(Simberloff 1974)
索引
Previous hypothesis to interpret low diversities on oceanic islands
• requiring more time to colonize

[Rejected] the saturated richness (in equilibrium) could be observed in some islands where the time is enough for the colonization

Equilibrium of species richness (種数平衡)

Saturation rate
Concept
Fig. 2. The numbers of land and freshwater bird species on various islands of the Moluccas, Melanesia, Micronesia, and Polynesia. Here the archiplagoes are widely scattered, and the distance effect is apparent in the greater variance. Hawaii is included even though its fauna is derived mostly from the New World (Mayr, 1943). "Near" islands (less than 500 miles from New Guinea) are enclosed in circles, "far" islands (greater than 2,000 miles) in squares, and islands at intermediate distances are left unenclosed. The saturation curve is drawn through large and small islands at source of colonization. (1) Wake, (2) Henderson, (3) Line, (4) Kusaie, (5) Tuamotu, (6) Marquesas, (7) Society, (8) Ponape, (9) Marianas, (10) Tonga, (11) Carolines, (12) Palau, (13) Santa Cruz, (14) Rennell, (15) Samoa, (16) Kei, (17) Louisiade, (18) D'Entrecasteaux, (19) Tanimbar, (20) Hawaii, (21) Fiji, (22) New Hebrides, (23) Buru, (24) Ceram, (25) Solomons, (26) New Guinea. (MacArthur & Wilson 1963)
Saturation rate vs distance from mother land
Concept
Fig. 3. Per cent saturation, based on the "saturation curve" of fig. 2, as a function of distance from New Guinea. The numbers refer to the same islands identified in the caption of fig. 2. Note that from equation (4) it is an oversimplification to take distances solely from New Guinea. The abscissa should give a more complex function of distances from all the surrounding islands, with the result that far islands would appear less "distant." But this representation expresses the distance effect adequately for the conclusions drawn.
Immigration curve vs extinction curve
Immigration rate, I - distance effect (+ richness in mother land)
Extinction rate, E - size effect (island area)
Replacement rate R, obtained by solving I = E
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.
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.

Island size                                                   Large             Small
Distance from mainland                              Close   Far     Close   Far
Immigration rate (移入率)                            High    Low    High     Low
Extinction rate (絶滅率)                               High    High    Low     Low
Equilibrium points of species (平衡点), s*   D         C         B         A

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)

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 (ゼロサムダイナミクス)

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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