Among the streams, invertebrate species of the Oberer Seebach (SB) followed
the maximum-likelihood predictions of the ZSM most closely, although the major-
ity of smaller and larger species departed from the model (Fig.8.3;Table8.2,
PCL¼0.496). There is a tailing-off of rare, large-sized species, indicating that, in
contrast to the ZSM prediction, there is dispersal limitation (m<1) in the SB. The
other two stream communities are not defined by this neutral assemblage con-
cept, as evident by high departures from ZSM predictions (Fig.8.3;Table8.2,Relative abundance (biomass)^100–810 –710 –610 –510 –410 –310 –210 –1100010 –810 –710 –610 –510 –410 –310 –210 –1100010 –810 –710 –610 –510 –410 –310 –210 –1(^100) PF
k^ =^ 0.125
PFk = 0.086
PFk = 0.159
SB
0
10 –10
10 –9
10 –8
10 –7
10 –6
10 –5
10 –4
10 –3
10 –2
10 –1
100
LL
(^010) Relative abundance (density)
(^10) –9
(^10) –8
(^10) –7
(^10) –6
(^10) –5
(^10) –4
(^10) –3
(^10) –2
(^10) –1
(^100)
1
MY
Species rank
0
10 –10
10 –9
10 –8
10 –7
10 –6
10 –5
10 –4
10 –3
10 –2
10 –1
100
101
PFk = 0.024
PFk = 0.108
PFk = 0.052
JM = 4.43 × 107
m = 0.99
JM = 2.45 × 106
m = 0.99
θ = 48.50
θ = 33.33
θ = 40.76
JM = 6.69 × 106
m = 1.00
(a) (b)
200 400 200 400 600
100 200 300 100200300400500
100 200 100 200 300 400
Figure 8.3Species-abundance distributions (SADs) shown with fits to the power-fraction
(PF) model and to the zero-sum multinomial (ZSM) neutral model in the three streams
Seebach (SB), Llwch (LL) and Mynach (MY). (a) Observed SADs based on biomass (symbols)
with fitted PF model (line and dotted line) superimposed. (b) Observed SADs based on
densities (symbols) with fitted PF and ZSM model (line and dashed lines) superimposed.
PFkis the estimatedk-value of the PF model;andmare the fundamental biodiversity
number and dispersal probability, respectively, andJMis the total number of individuals
for the ZSM model. Dotted and dashed lines are the 95% confidence limits of the PF and
ZSM model, respectively. Details of estimated parameter values are given in Table8.2.
150 P.E. SCHMID AND J. M. SCHMID-ARAYA