Interspecific interaction (異種個体間相互作用)

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)

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

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

Indexces of interspecific interaction

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

(Armas et al. 2004)

RII

B_w: biomass observed by the target plant grown with other plants
B_o: biomass potentially achieved without species interactions
ΔB_F: an increase of biomass produced by facilitation (from 0 to +∞)
ΔB_C: decrease caused by competition

ΔB_FC: observed biomass change = absolute effect of the interaction

-B_o ≤ ΔB_FC ≤ +∞

if only facilitation occurs, ΔB_FC ranges from 0 to 1

if only competition occurs, ΔB_FC 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

= ΔB_FC/(ΔB_FC + 2B_o)
= (B_w - B_o)/(B_w + B_o), RII = [-1, 1]

Natural enemy (天敵)

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

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

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

__(a)_______________(b)_________________(c)

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

⇔ Intraspecific competition: competition between members of the same species