Species richness-standing crop relationship in stream bryophyte communities: patterns across multiple scales

Virtanen, R Muotka, T Saksa, M

R. Virtanen et al., Species richness-standing crop relationship in stream bryophyte communities: patterns across multiple scales, J ECOLOGY, 89(1), 2001, pp. 14-20

34

INGLESE

Article

Environment/Ecology

JOURNAL OF ECOLOGY

0022-0477 → ACNP

89

1

2001

14 - 20

ISI

0022-0477(200102)89:1<14:SRCRIS>2.0.ZU;2-R

1 We tested for a unimodal ('hump-backed') relationship between species ric hness and standing crop at various spatial scales in stream bryophyte commu nities. Bryophyte species and their biomasses were determined from 20 to 25 quadrats in eight river and six stream sites in northern Finland. 2 Regression analyses revealed a quadratic relationship between richness an d biomass in only two of the river sites and a positive correlation in one other. A quadratic relationship was detected in three stream sites and rich ness increased linearly with biomass in another. 3 We also tested for the hump-shaped pattern across individual stream bould ers, representing an elevational gradient from continuously submerged to pe rmanently dry conditions. with an intermediate zone with fluctuating water level. 4 Species richness-standing crop relationship conformed to the hump-backed model only when samples from all three microhabitats were included in the a nalysis. A significant positive correlation occurred in the exposed low bio mass end of the gradient which is characterized by semi-aquatic species, wh ereas the relationship tended to be negative in permanently submerged areas with high biomass of large canopy-forming species. Quadrats close to the w ater level had intermediate standing crop and highest species richness. 5 Species dominant at either end of the gradient appeared unable to monopol ize space in the intermediate zone where disturbances (e.g. scouring by ice ) detach mosses from the substratum, creating vacant gaps for colonization. The unimodal relationship between richness and biomass is likely to occur only in streams that contain large boulders protruding above the water line , thus providing scope for community diversification along very short verti cal distances.