Abstract

Species distribution data provide the foundation for a wide range of ecological research studies and conservation management decisions. Two major efforts to provide marine species distributions at a global scale are the International Union for Conservation of Nature (IUCN), which provides expert-generated range maps that outline the complete extent of a species' distribution; and AquaMaps, which provides model-generated species distribution maps that predict areas occupied by the species. Together these databases represent 24,586 species (93.1% within AquaMaps, 16.4% within IUCN), with only 2,330 shared species.

Differences in intent and methodology can result in very different predictions of species distributions, which bear important implications for scientists and decision makers who rely upon these datasets when conducting research or informing conservation policy and management actions. Comparing distributions for the small subset of species with maps in both datasets, we found that AquaMaps and IUCN range maps show strong agreement for many well-studied species, but our analysis highlights several key examples in which introduced errors drive differences in predicted species ranges. In particular, we find that IUCN maps greatly overpredict coral presence into unsuitably deep waters, and we show that some AquaMaps computer-generated default maps (only 5.7% of which have been reviewed by experts) can produce odd discontinuities at the extremes of a species’ predicted range.

We illustrate the scientific and management implications of these tradeoffs by repeating a global analysis of gaps in coverage of marine protected areas, and find significantly different results depending on how the two datasets are used. By highlighting tradeoffs between the two datasets, we hope to encourage increased collaboration between taxa experts and large scale species distribution modeling efforts to further improve these foundational datasets, helping to better inform science and policy recommendations around understanding, managing, and protecting marine biodiversity.

Figures from manuscript

Figure 1:

fig 1

Fig 1. Taxonomic and geographic coverage of AquaMaps and IUCN range data. (A) Number and proportion of species by taxa included in each dataset (22,889 species in AquaMaps, 4,027 species in IUCN). Overlapping species are dominated by bony fishes (994 species, primarily tropical taxa) and corals (394 species). (B, C) Global marine species count per 0.5° cell according to (B) AquaMaps and © IUCN. The margin frequency plots show relative species count per cell at each latitude and longitude.


Figure 2:

fig 2

Fig 2. Comparison of alignment between AquaMaps and IUCN range data. (A) Distribution alignment (overlap of smaller range within larger) versus area ratio (the ratio of smaller range area to the larger range area) for 2,330 species included in both IUCN and AquaMaps datasets. The upper right quadrant comprises species whose maps largely agree in both spatial distribution and the extent of described ranges (n = 522; 22.4% of paired map species). The upper left quadrant comprises species whose maps agree well in distribution, but disagree in area (n = 715; 30.7%). The lower right quadrant includes species for which the paired maps generally agree in range area, but disagree on where those ranges occur (n = 649; 27.9%). The lower left quadrant indicates species for which the map pairs agree poorly in both area and distribution (n = 444; 19.1%). (B) Alignment quadrant breakdown of species by taxonomic group.


Figure 3:

fig 3

Fig 3. Effect of 200 m depth constraint on IUCN range maps for coral species. (A) Aggregate map combining ranges of the 562 coral species mapped in the IUCN dataset, showing raw ranges and ranges clipped to 200 m depth. (B) Alignment quadrant breakdown of paired map coral species using original data from IUCN and AquaMaps (as in Fig 2B) and the same species with IUCN ranges clipped to 200 m depth.


Figure 4:

fig 4

Fig 4. Effect of FAO Major Fishing Area constraints on AquaMaps distributions. (A) AquaMaps species distribution of Hoplichthys regani, the ghost flathead, with known occurrence records. (B) Aggregated AquaMaps predicted ranges for 3,208 species whose equatorial distribution encounters an eastern discontinuity exactly at 175° W, the boundary between FAO Major Fishing Areas 71 and 77 (shown in blue). Other FAO area boundaries create additional clear discontinuities.


Figure 5:

fig 5

Fig 5. MPA gap analysis results based upon alternate choices of datasets. Percent of species range covered by MPAs based upon methods in Klein et al. (2015). Scenario 1 replicates the original results, measuring protected range of species in AquaMaps version 08/2013 dataset, with a 50% presence threshold, against the 2014 World Database of Protected Areas, filtered for IUCN categories I-IV that overlap marine areas. Scenario 2 updates the results using AquaMaps version 08/2015, showing very small changes despite the inclusion of an additional 5,545 species. Scenario 3, still using 2015 AquaMaps data, drops the presence threshold to zero, showing an expected decrease in gap species, but also a decrease in species with 5% or greater protected range. Scenario 4 examines species MPA coverage using only the IUCN dataset.

Alignment comparison of paired maps

Overlaying paired distribution maps for each species, we defined and calculated distribution alignment, which compares how well the two maps agree based on the amount of the smaller range that overlaps the larger range; and area ratio, which compares the range size predicted by each map, based on the ratio of the smaller range to the larger range.

Plotting the distribution alignment and area ratio for each of the 2,330 species in both datasets, we defined quadrants based on how well the maps aligned for each species.

This plot corresponds to Fig 2A from the published paper and Fig S4A from the supporting information.


For each taxonomic group (based on IUCN dataset), we determined the breakdown of how each group fell into each of the four quadrants. This plot corresponds to Fig 2B from the published paper and Fig S4B from the supporting information.

Individual Species Maps

The grey borders noted in the ocean basins represent boundaries of the United Nations Food and Agriculture Organization (FAO) Major Fishing Areas[16]. These boundaries are used in the AquaMaps methodology to constrain model predictions.

Coral Species Maps

IUCN range maps frequently include a 50 km coastal buffer for coastal species, which can distort predictions of presence for coastal species such as corals. The IUCN marine species range map dataset[2] includes maps for 562 species (394 of which are mapped in both IUCN[2] and AquaMaps[1] datasets). According to IUCN habitat data for all corals included in the IUCN dataset, none of these mapped species are found below 200 m depth; only one species just reaches 200 m, and 94% occur only in waters shallower than 50 m.

This plot corresponds to Fig 3A from the published paper; the mini quad-plot corresponds to Fig S5 from the supporting information.

By constraining IUCN ranges for corals to depths less than 200 meters, we reduce the IUCN predicted range without affecting the AquaMaps predicted range. In so doing, we remove a source of commission error caused by IUCN inclusion of an artificial 50 km coastal buffer into inappropriately deep areas; this typically improves the area ratio alignment without significantly reducing the distribution alignment.

This plot corresponds to Fig 3B from the published paper.

References

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Supporting Information for manuscript

Figure S1:

s1 fig

S1 Fig. Examples of AquaMaps and IUCN raw species range data for Thunnus alalunga (Albacore Tuna). (A) IUCN species distribution represented as extent of occurrence polygons. (B) AquaMaps species distribution represented as varying probabilities of occurrence assigned to 0.5° grid cells. © IUCN and (D) AquaMaps distributions recalculated to represent presence within 0.5° grid cells.


Figure S2:

s2 fig

S2 Fig. Rasterizing shapefiles provided by IUCN. A portion of the T. alalunga range map is used to exemplify the rasterization process. To enable direct comparison of IUCN species ranges to AquaMaps species ranges, the raw IUCN polygon (A) is overlaid with a 0.5° degree grid matching the AquaMaps grid (B). Each cell is assigned a value of “present” if the cell overlaps any portion of the polygon ©. The resulting raster (D).


Figure S3:

s3 fig

S3 Fig. Representative species maps to illustrate each quadrant from Fig 2A. Each map is positioned to match its quadrant in Fig 2A. FAO Major Fishing Area boundaries [16] are outlined in light grey. (A) Distribution-aligned: Conus episcopatus, the dignified cone snail. Distributions show excellent overlap in the western Pacific, though IUCN range extends well beyond the bounds of the AquaMaps range. (B) Well-aligned: Kajikia albida, the Atlantic white marlin. Distributions from each data set show nearly complete overlap, and very similar range size. © Poorly aligned: Acanthurus nigroris, the blue-lined surgeonfish. IUCN predicts species distribution only near the Hawaiian islands; AquaMaps predicts extensive distribution throughout the central and western Pacific Ocean. The datasets align in neither distribution nor range size. (D) Area-aligned: Conus magnificus, the magnificent cone snail. Distributions overlap in the southern Pacific, but align poorly elsewhere. The range sizes are similar.


Figure S4:

s4 fig

S4 Fig. Improvement in alignment due to expert review of AquaMaps. (A) Modification of Fig 2A to highlight species with expert-reviewed AquaMaps shows that the mean distribution alignment and mean area ratio both improve. (B) Including only expert-reviewed species in each quadrant shows increased membership in the well-aligned and distribution-aligned quadrants relative to Fig 2B.


Figure S5:

s5 fig

S5 Fig. Shift in alignment of paired-map coral species due to clipping IUCN ranges to areas shallower than 200 m. The grey lines represent the change in apparent alignment for a single species. Most coral species shift rightward from the upper left quadrant to the upper right, improving in area alignment with little if any loss in distribution alignment, since in general, only unsuitable habitat has been removed. Leftward shifts can be seen in species whose larger original range is represented in AquaMaps; by trimming IUCN ranges, the area ratio becomes smaller.


S1 Fig and S2 Fig references

  1. www.aquamaps.org, version of Aug. 2013. Reviewed distribution maps for Thunnus alalunga (Albacore), with modeled year 2100 native range map based on IPCC A2 emissions scenario. Web. Accessed 11 Sep. 2016.
  2. International Union for Conservation of Nature (IUCN) 2011. Thunnus alalunga. The IUCN Red List of Threatened Species. Version 2016-2.

S3 Fig references

  1. www.aquamaps.org, version of Aug. 2013. Computer generated distribution maps for Conus episcopatus, with modeled year 2100 native range map based on IPCC A2 emissions scenario. Web. Accessed 11 Sep. 2016.
  2. Conch Books, Hackenheim, Germany 2013. Conus episcopatus. The IUCN Red List of Threatened Species. Version 2016-2.
  3. www.aquamaps.org, version of Aug. 2013. Computer generated distribution maps for Kajikia albida (Atlantic white marlin), with modeled year 2100 native range map based on IPCC A2 emissions scenario. Web. Accessed 11 Sep. 2016.
  4. International Union for Conservation of Nature (IUCN) 2011. Kajikia albida. The IUCN Red List of Threatened Species. Version 2016-2.
  5. www.aquamaps.org, version of Aug. 2013. Reviewed distribution maps for Acanthurus nigroris (Bluelined surgeonfish), with modeled year 2100 native range map based on IPCC A2 emissions scenario. Web. Accessed 11 Sep. 2016.
  6. International Union for Conservation of Nature (IUCN) 2012. Acanthurus nigroris. The IUCN Red List of Threatened Species. Version 2016-2.
  7. www.aquamaps.org, version of Aug. 2013. Computer generated distribution maps for Conus magnificus, with modeled year 2100 native range map based on IPCC A2 emissions scenario. Web. Accessed 11 Sep. 2016.
  8. Conch Books, Hackenheim, Germany 2013. Conus magnificus. The IUCN Red List of Threatened Species. Version 2016-2.