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Diatoms often break the smaller-when-warmer rule
Across a 20°C Icelandic stream gradient, diatom size did not shrink with warmth; composition, not plastic shrinkage, drove size differences.
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What climate-ecology rule were the diatoms testing?
Whether warmer water produces smaller diatoms within species (James’ rule) and at the community level (Bergmann’s rule).
Source: Diatoms can be an important exception to temperature-size rules at species and community levels of organization · DOI · quote verified
Why is a geothermal catchment a useful warming proxy?
Fourteen streams spanned a 20°C difference but were no more than 2 km apart, limiting biogeography and many covariates.
Source: Diatoms can be an important exception to temperature-size rules at species and community levels of organization · DOI · quote verified
How many species and streams entered the size analysis?
31 species in two or more of 14 streams; 75 species were detected overall.
Source: Diatoms can be an important exception to temperature-size rules at species and community levels of organization · DOI · quote verified
Did species consistently shrink with temperature?
No: 16 negative and 15 positive slopes; combined P=0.186 against a shrinking hypothesis.
Source: Diatoms can be an important exception to temperature-size rules at species and community levels of organization · DOI · quote verified
Was there a community-level size–temperature relationship?
No clear relationship; weighted linear and quadratic regressions were not significant (P=0.2628 and 0.3785).
Source: Diatoms can be an important exception to temperature-size rules at species and community levels of organization · DOI · quote verified
What mostly caused community size differences among streams?
Compositional shifts: 51 of 91 pairs were solely compositional; only four were solely intraspecific.
Source: Diatoms can be an important exception to temperature-size rules at species and community levels of organization · DOI · quote verified
When both mechanisms mixed, how large was the intraspecific share?
On average 21.8% (range 0.28–84.4%) of the 36 mixed comparisons.
Source: Diatoms can be an important exception to temperature-size rules at species and community levels of organization · DOI · quote verified
Did species turnover dominate compositional change?
No. Turnover averaged 14.8% of compositional differences; relative-abundance shifts were the main route.
Source: Diatoms can be an important exception to temperature-size rules at species and community levels of organization · DOI · quote verified
Was temperature a stronger size driver than pH or silicate?
Not in this catchment: other variables sometimes showed stronger community-size patterns despite much smaller ranges.
Source: Diatoms can be an important exception to temperature-size rules at species and community levels of organization · DOI · quote verified
Why would a diatom exception matter globally?
Diatoms account for around 23% of world primary production and their size affects food webs and carbon cycling.
Source: Diatoms can be an important exception to temperature-size rules at species and community levels of organization · DOI · quote verified
What do the authors conclude about ‘universal’ shrinking with warming?
Diatoms in this natural community do not support universal smaller-when-warmer rules at species or community levels.
Source: Diatoms can be an important exception to temperature-size rules at species and community levels of organization · DOI · quote verified
Why can lab single-species results mislead here?
Intraspecific (plastic) size changes were a much smaller field contributor than compositional shifts among species.
Source: Diatoms can be an important exception to temperature-size rules at species and community levels of organization · DOI · quote verified