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, 6 (5), e19653

Current and Future Patterns of Global Marine Mammal Biodiversity

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Current and Future Patterns of Global Marine Mammal Biodiversity

Kristin Kaschner et al. PLoS One.

Abstract

Quantifying the spatial distribution of taxa is an important prerequisite for the preservation of biodiversity, and can provide a baseline against which to measure the impacts of climate change. Here we analyse patterns of marine mammal species richness based on predictions of global distributional ranges for 115 species, including all extant pinnipeds and cetaceans. We used an environmental suitability model specifically designed to address the paucity of distributional data for many marine mammal species. We generated richness patterns by overlaying predicted distributions for all species; these were then validated against sightings data from dedicated long-term surveys in the Eastern Tropical Pacific, the Northeast Atlantic and the Southern Ocean. Model outputs correlated well with empirically observed patterns of biodiversity in all three survey regions. Marine mammal richness was predicted to be highest in temperate waters of both hemispheres with distinct hotspots around New Zealand, Japan, Baja California, the Galapagos Islands, the Southeast Pacific, and the Southern Ocean. We then applied our model to explore potential changes in biodiversity under future perturbations of environmental conditions. Forward projections of biodiversity using an intermediate Intergovernmental Panel for Climate Change (IPCC) temperature scenario predicted that projected ocean warming and changes in sea ice cover until 2050 may have moderate effects on the spatial patterns of marine mammal richness. Increases in cetacean richness were predicted above 40° latitude in both hemispheres, while decreases in both pinniped and cetacean richness were expected at lower latitudes. Our results show how species distribution models can be applied to explore broad patterns of marine biodiversity worldwide for taxa for which limited distributional data are available.

Conflict of interest statement

Competing Interests: The authors have declared that no competing interests exist.

Figures

Figure 1
Figure 1. Predicted patterns of marine mammal species richness.
A. All species (n = 115), B. Odontocetes (n = 69), C. Mysticetes (n = 14), D. Pinnipeds (n = 32). Colors indicate the number of species predicted to occur in each 0.5°x0.5° grid cell from a relative environmental suitability (RES) model, using environmental data from 1990–1999, and assuming a presence threshold of RES>0.6.
Figure 2
Figure 2. Marine mammal species richness by latitude.
Number of predicted species was summed over 5° latitudinal bands for all species, mysticetes, small odontocetes, large odontocetes (beaked whales and sperm whale), and pinnipeds.
Figure 3
Figure 3. Rate of species discovery with survey effort.
Number of species detected with increasing sampling effort in each 5°x5° cell in A. Antarctic waters, B. The Northeastern Atlantic, C. The Eastern Tropical Pacific, D. Species accumulation curves in different survey areas.
Figure 4
Figure 4. Validation with empirically observed marine mammal occurrences (5°x5° cells, 1990–1999).
A. Predicted species richness of all cetaceans (RES presence threshold >0.6), B. Observed cetacean species richness per standardized sample of 50 sightings (grey cells have been covered by surveys but had insufficient effort for analysis), C. Relationship between observed and predicted species richness in the Antarctic (red), North Atlantic (blue) and Eastern Tropical Pacific (green) and across all three surveys (black). Data points correspond to individual 5°grid cells, regression lines to best linear fits, r2 values were corrected for spatial autocorrelation.
Figure 5
Figure 5. Projected effects of climate change on marine mammal species richness.
Projected changes in overlap of optimal habitat across all species from 1990–1999 to 2040–2049 using the IPCC-A1B climate change scenario (0.5°×0.5° grid cells) A. Loss in number of native species, B. Gain in number of new species. Biodiversity changes are expressed relative to species richness predicted for the 1990s, and assuming a presence threshold of RES>0.6.
Figure 6
Figure 6. Projected absolute and proportional changes in marine mammal species richness and community composition at different latitudes.
Changes were calculated relative to predicted species richness for the 1990s summed over 5° latitudinal bands for mysticetes, small odontocetes, large odontocetes, and pinnipeds.

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