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Interspecific interaction (種間相互作用)

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

Interspecific interaction (異種個体間相互作用)

Interrelationships between populations

predation (捕食) (+/-)
competition (競争) (-/-)
cooperation (+/+, +/0, +/-)

mutualism (双利共生) (+/+), commensalism (片利共生) (+/0)

+ natural selection

Antagonism (拮抗作用)

Parasitism (寄生)
[+ parasite, – host]

Adelphoparasite (同種寄生): a parasite that is closely related to its host (e.g., both placed in the same family)

Ectoparasite [+, -], external paratisism (外部寄生): a parasite living on the outside of its host

haustorium (pl. -a, 吸器): that protion of a parasite that penetrates host cells and absorbs nutrients

Endoparasite [+, -], internal paratisism (内部寄生): a parasite living within the host

Indexces of interspecific interaction

  • RII (relative interaction intensity)
  • RCI (relative competition index)
  • RNE (relative neighbor effect)
  • lnRR (log response ratio)

(Armas et al. 2004)

Bw = Bo + ΔBF - ΔBC

Bw: biomass observed by the target plant grown with other plants
Bo: biomass potentially achieved without species interactions
ΔBF: an increase of biomass produced by facilitation (from 0 to +∞)
ΔBC: decrease caused by competition


ΔBFC: observed biomass change = absolute effect of the interaction

Bw - Bo = ΔBFC

-Bo ≤ ΔBFC ≤ +∞


if only facilitation occurs, ΔBFC ranges from 0 to 1

BFC| ≤ |ΔBFC + Bo|

if only competition occurs, ΔBFC is negative but the above equation may not be true, as the index has an unlimited range [-∞ 0]
Facilitation and comopetition would not be comparable using these equations. Therefore, new index, RII, is proposed

RII = (ΔBF - ΔBC))/((ΔBF + Bo) + (-ΔBC + Bo))

= ΔBFC/(ΔBFC + 2Bo)
= (Bw - Bo)/(Bw + Bo), RII = [-1, 1]

Predation (捕食)

Natural enemy (天敵)

k(N): ratre of predation - number of preys ingested by a predator in a given time
N: population density of prey

1. k(N) = kN: Lotka-Volterra
2. k(N) = kN/(1 + N) saturation
3. k(N) = kN2/(1 + N2) switching

what equation (1-3) is apporpriate is determined by the prey-predator interaction


number of predators: Y = constant
1. dN/dt = r(1 – N/k)nk(N)Y___(k(N) = kN same with capturing)

A: assuming that the number of individuals follows logistic growth
B: speed of prays fed by the predator

2. dN/dt = r[1 – N/kp/(1 + n)]n___(p = kY/N)

p > p*: extinction
at this time, Y* = r(1 + k)2/(4nK)

3. dN/dt = r[1 – n/Kpn/(1 + n2)]n


(a) two stable systems exist
(b) sudden decrease at p* but will not be extinct
(c) increasing number of preys explosively

Interspecific competition (種間競争)

Def. competition in which individuals of different species compete for the same resources in an ecosystem

⇔ Intraspecific competition: competition between members of the same species