January 27, 2021


It's Your Education

Response to Remark on “Global distribution of earthworm diversity”


James et al. declare that there are areas of concern in our perform. We believe that that they have misunderstood the techniques powering our paper and that discrepancies in scale have been forgotten. At the time these misunderstandings have been fixed, their remaining criticisms are either not sustained or concur with our statements. To advance the industry, we advise more sampling employing similar methodologies in underrepresented parts.

Criticisms of our paper (1) by James et al. (2) can be broken into 3 most important regions: (i) criticisms of the conclusions, (ii) criticisms of the data employed, and (iii) criticisms of including anthropogenic habitats.

James et al. improperly assert that we “conclude that tropical earthworm communities are fewer diverse and ample than temperate communities.” In point, we conclude that “it is most likely that the tropics harbor extra species all round,” as demonstrated by determine 2 of (1). Nonetheless, we want to draw focus to other worldwide distribution studies that also discovered decrease local soil biodiversity in tropical soils relative to temperate or arctic areas [e.g., microbes (3), nematodes (4)]. James et al. also assert that employing nearby or website-degree estimates of variety to fully grasp world-wide patterns is not acceptable (2). This is not accurate, as diverse scales of range can be utilized to test ecological ideas, this sort of as the latitudinal variety gradient (5). Our modeled outputs offer a common sample, and discrepancies are predicted to occur if it have been to be floor-truthed.

We applied transparent inclusion requirements [see “Literature search” in supplementary materials of (1)] for papers screened, which is a required approach in synthesis experiments (6) and is vital when data have been collected utilizing diverse methodologies. This resulted in removal of 92.3% of papers, which is not an exceptionally significant proportion. For case in point, a really cited ecological meta-evaluation (7) eliminated 90.6% of papers in the course of the screening course of action. However, we worry that it was not required for datasets to consist of species-level identification, as stated in (2).

James et al. provide a checklist of publications that look to contradict our results. These papers are highly instructive in terms of earthworm inventories, but their effects are not straight comparable to our review. Most of the papers outlined in (2) do not give α-amount (area-amount) estimates of earthworm diversity that are satisfactory to make it possible for a quantitative analysis, these as ours, to be carried out. In (1), we defined “local” in terms of web page-amount data, where by a “site” was described as “a site of a person or more samples that adequately captured the earthworm local community.” In a number of the listed papers, this sort of as (8) [their reference 5; note that the values reported in (2) do not match the actual values in this publication], the values presented are totals of various sampling web pages (employing our definition), and hence not α-diversity, but instead general variety inside a larger region. The literature presented does not contradict our summary, but as a substitute reinforces that there are most likely high concentrations of β-diversity of earthworms in the tropics.

James et al. also focus on the sampling curves of earthworm species inside of temperate and tropical biomes. However, as no quotation was supplied, we are not able to set up the foundation of these promises. Having said that, supplied our results in determine 2 of (1) (higher regional variety, implying substantial β-variety when local range is minimal), we would not argue versus this issue.

In (2) the spatial biases in our data had been also mentioned. We experienced previously highlighted in (1) that we have to have additional sampling in the tropics and other underrepresented places. Determine 2 of (1) was not meant to exhibit exactly where upcoming sampling must take place (as longitude ought to also be taken into account for this kind of tips), but instead to account for the simple fact that there was significantly less sampling across selected wide latitudinal zones. So, we reiterate our phone, adding to remarks in (2), for more sampling not only in the tropics but also in several other sites, like underrepresented temperate zones this kind of as Russia [see figure 1A of (1)].

The taxonomic skills of our info contributors was also named into question by James et al. We had already highlighted the large proportion of unidentified species in the tropics in our text as properly as in desk S4 of (1). Nonetheless, we do disagree with (2) pertaining to identification expertise needed for the temperate realm, as there are also several species in temperate areas that are not able to be recognized by external functions alone. In addition, the taxonomy presented in (1) was checked by multiple earthworm taxonomists, and so we stand by its dependability. But we wholeheartedly concur that far more taxonomists are necessary globally to support enhance recent understanding of earthworm geographic patterns.

All over (2), extra strategies of sampling earthworm communities had been instructed. Whilst we agree with these strategies, we anxiety that they are appropriate only in specific situations. Qualitative methods (e.g., a totally free research for earthworms at a web-site) are typically utilized for species inventories, and we agree with (2) that this would give bigger numbers of earthworm species in an area. Even so, owing to a absence of a standardized sample work and region, qualitative approaches are not similar across reports. Conversely, quantitative approaches (e.g., hand-sorting by means of soil within a 50 cm × 50 cm quadrat) usually use standardized methods that are equivalent throughout scientific studies but are unlikely to detect every single species that could be existing at a certain habitat or site (in individual, those affiliated with particular microhabitats or microsites, this sort of as dead logs or compost piles). In (1) we essential similar benefits to let us to examine a big set of standardized quantitative facts and to minimize the full variation associated with the collated datasets. Therefore, commonly taxonomic literature (e.g., reporting species’ presence or absence employing qualitative methods) was excluded, and as a end result, there will be a bias toward less scarce species. Although DNA barcoding would be useful for upcoming global synthesis experiments, there are not however ample info for this kind of reports. Also, quite a few reports [e.g., (9)] have described the existence of cryptic species in the temperate realm, so variety outside the tropics is also anticipated to enhance as a final result of applying molecular procedures.

In a entire world undisturbed by anthropogenic things to do, we would predict significant-scale biogeographic patterns using only knowledge from all-natural habitats. Even so, mainly because human impacts are triggering unparalleled amounts of land use alter (10) and due to the fact there are fairly few places of organic habitats in components of the entire world (e.g., Europe), anthropogenic habitats require to be regarded as in biodiversity studies. To existing the most practical watch possible of current earthworm communities, we integrated a world wide layer on habitat address inside our products [see figures S5 and S6 of (1)]. If these habitats comprise fewer species, we felt it was important to show the impression of this across a worldwide scale, instead than excluding these increasing programs [e.g., agriculture covers 37% of Earth’s land (11)] from our examination. The distribution of every classification of habitat include was comparatively even across temperate and tropical regions in (1), although some disparity existed (e.g., 22.2% of internet sites in the tropics, but only 14.9% of web sites in the temperate area, were determined as “cropland”).

At last, we would like to emphasize again that with far more information, the reliability of conclusions can only be improved, and we welcome any further sampling employing similar methodologies in underrepresented regions. Nevertheless, it is important that these facts are built freely accessible, possibly in unique publications or in on-line repositories.

This response has been submitted on behalf of all co-authors of (1), with their awareness.


  1. J. Koricheva, J. Gurevitch, K. Mengersen, Handbook of Meta-Analysis in Ecology and Evolution (Princeton Univ. Press, 2013).

  2. IPBES, Summary for Policymakers of the Global Assessment Report on Biodiversity and Ecosystem Companies of the Intergovernmental Science-Policy Platform on Biodiversity and Ecosystem Solutions (2019), p. 56.