Correction to ‘Latitudinal gradients in biotic niche breadth vary across ecosystem types’

Proc. R. Soc. B 282, 20151589 (Published Online 11 November 2015) (doi:10.1098/rspb.2015.1589)

Purpose for correction

A subset of food webs analysed for the manuscript Latitudinal gradients in biotic niche breadth vary across ecosystem types; (doi:10.1098/rspb.2015.1589) had formatting errors or irregularities that caused them to be incorrectly processed by our original code (75 out of 263; see the electronic supplementary material, table S2, appendix S1 for details). Some food webs had inconsistent labels that prevented sets of predators and prey from being correctly linked to the same species. Others listed interactions using categorical symbols; these interactions were not included in our original analyses.

We have corrected these inconsistencies and repeated our analyses to ensure that our conclusions did not change. After re-analysis, our results were qualitatively identical to those originally published and our original conclusions hold. However, the specific values for correlations and scaling relationships given in the original results and discussion are incorrect. Below, we present the section Results and the beginning of the last paragraph of the section Discussion (the only portion to require correction). All corrections are highlighted in bold. The original and corrected values may be compared in tables 1 and 2. We also show the original and corrected figures 2 and 3. All supplemental figures have also been updated; as with the main-text figures below, any differences were minor. Reference numbers are as in the original main text.

Table 1.

Original and corrected values for correlations, mean generalities and a Student’s T-test for differences in mean generalities reported in the main text. (The ‘Location’ column indicates the section in which the relationship is described. Original values are those given in the original publication of this article. Corrected values are those obtained after correcting formatting inconsistencies in several food webs.)

relationship	location	original	corrected
	results	0.891	0.915
	results	>0.999	>0.999
	results	0.890	0.912
	discussion	5.47	5.86
	discussion	3.82	3.75
P()	discussion	0.007	<0.001

Table 2.

Original and corrected values for scaling relationships between specialization and species richness and the effect of latitude on the strength of these relationships. (Original values are those given in the original publication of this article. Corrected values are those obtained after correcting formatting inconsistencies in several food webs. All values are referred to in the Results section of the main text.)

parameter	original		corrected
scaling of specialization with species richness
	0.637	<0.001	0.688	<0.001
	0.553	<0.001	0.658	<0.001
	0.637	<0.001	0.695	<0.001
strength of scaling and latitude: estuarine, marine, terrestrial
	−0.001	0.365	−0.001	0.210
	−0.001	0.535	−0.001	0.315
	−0.001	0.366	−0.001	0.205
strength of scaling and latitude: lakes
	0.004	0.019	0.003	0.031
	0.005	0.004	0.005	0.005
	0.004	0.018	0.004	0.030
strength of scaling and latitude: streams
	n.a.		n.a.
	0.007	0.001	0.005	0.008
	n.a.		n.a.

Figure 2.

Scaling relationships for re-scaled link density, generality, and vulnerability relative to the species richness of a food web. Here we show the original relationships (a) and the relationships after correcting several food webs (b). Link density, generality and vulnerability were each re-scaled to remove the effects of latitude and ecosystem type. As these relationships take the form of power laws, we did this by dividing the food-web property (e.g. link density) by species richness raised to an exponent including the effects of latitude and, where applicable, ecosystem type and the interaction between ecosystem type and latitude. Note that in all cases estuarine food webs were treated as the baseline ecosystem type, but that at most two ecosystem types had interactions between ecosystem type and latitude retained in the best-fit model (see section Results for specifics). For each relationship, we show the re-scaled values (white circles) as well as the overall scaling relationship using estuarine ecosystems as a baseline (black line, n = 196 food webs). For a figure with the uncorrected values, see the electronic supplementary material, figure S7 and appendix S4. Note that the corrected and original relationships are very similar, but the re-scaled values for some food webs have changed.

Figure 3.

Changes to the scaling of link density, generality and vulnerability with species richness across ecosystem types and over latitude. Here we show these changes for the original dataset (a) and after correcting several food webs (b). We show the estimated scaling exponent for species richness (black line) with its 95% confidence interval (in grey), based on n = 196 empirical food webs. Latitude is given in degrees from the equator regardless of direction. Note that the scaling relationships with latitude were very similar for the original and corrected datasets.

Results

Link density (mean number of feeding links per species), generality (mean number of prey per species) and vulnerability (mean number of predators per species) were strongly and positively correlated ( for link density and generality, for link density and vulnerability, and for generality and vulnerability; table 1) . Contrary to the expected latitudinal gradient, the best-fit version of equation (1) did not include a significant effect of latitude on species richness for any ecosystem type. Further, there were no significant relationships between link density, generality or vulnerability with latitude for any ecosystem type.

Each measure of specialization increased with increasing species richness (, ; , ; and , , respectively; table 2 and figure 2). For estuarine, marine and terrestrial food webs the strength of this scaling did not vary with latitude (, for link density; , for generality; and , for vulnerability; table 2; figure 3). In lake food webs, however, the scaling of each property was stronger towards the poles (, ; , ; and , , respectively; table 2). In stream food webs, generality increased more rapidly towards the poles (, ; table 2) while link density and vulnerability did not vary with latitude (i.e. the interaction term was not retained in the best-fit models).

Discussion

Importantly, while terrestrial communities are also strongly seasonal at high latitudes and can receive significant allochthonous inputs [46], terrestrial consumers tend to be morphologically specialized for feeding on particular prey [53]. This means that primarily gape-limited aquatic consumers tend to be more generalist across all types of aquatic habitats than terrestrial consumers [5,53]. This trend also held in our data, although the difference between generality was not significant (, ; for ; table 1). The key to this argument is therefore whether freshwater ecosystems experience more severe seasonal variation than marine and estuarine ecosystems.