Tittensor et al. 2010

Question 1

Why is this paper important?

Answer 1

Our understanding of global marine diversity is limited, with recent findings revealing some striking contrasts to widely held terrestrial paradigms

The paper investigates whether observed patterns were consistent with mechanisms proposed to structure global-scale species diversity patterns, and how marine richness overlapped with recently mapped cumulative human impacts across the world ocean

Question 2

What is the extent of the paper?

Answer 2

The authors compiled data on >11,500 species from 13 taxons

Question 3

What are the global patterns of marine diversity found in this paper?

Answer 3

There are two distinct patterns:

Primarily coastal taxa had peaks of diversity in the western Pacific and showed clear latitudinal gradients along the coasts of continents

Primarily oceanic taxa tended to show pantropical or circumglobal distributions with diversity peaking at latitudes between 20^o and 40^o in all oceans

Question 4

Where is the species richness of coastal taxa concentrated?

Answer 4

Coastal species groups tended to be disproportionally concen- trated in Southeast Asia (Fig. 2c)

Question 5

Where is the species richness of oceanic taxa concentrated?

Answer 5

Primarily oceanic taxa tended to show pantropical or circumglobal distributions with diversity peaking at latitudes between 20^o and 40^o in all oceans

Question 6

What is the pattern of total species richness?

What contributes most to the pattern of total species richness?

Answer 6

regional peaks in Southeast Asia (Pacific), Southeast Africa (Indian) and the Caribbean (Atlantic)

Total species richness across taxa was mostly driven by fishes

Question 7

Which hypotheses do the authors test?

Answer 7

(1) The kinetic energy or temperature hypothesis
(2) The potential energy or ‘productivity-richness’ hypothesis
(3) The stress hypothesis
(4) The climate stability hypothesis
(5) The availability of important habitat features
(6) signatures of evolutionary history among ocean basins

Question 8

what is the kinetic energy or temperature hypothesis ?

Answer 8

higher temperatures increased metabolic rates may promote higher rates of speciation leading to greater diversity, or that range limits are set by thermal tolerance, with more species tolerant of warm conditions

Question 9

What is the potential energy or ‘productivity-richness’ hypothesis?

Answer 9

The potential energy or ‘productivity-richness’ hypothesis pre- dicts a positive effect of primary productivity on richness at coarse grain sizes, such as facilitating larger population sizes that avert extinctions or support niche specialists5,13,15. Peaks of temperature and productivity are spatially separated in the ocean, allowing better discrimination of these first two hypotheses than on land.

Question 10

What is the stress hypothesis?

Answer 10

The stress hypothesis predicts a negative relationship of rich- ness with environmental stress16, tested by quantifying the extent of oxygen depletion, a unique and increasingly important stressor in the marine environment

Question 11

what is the climate stability hypothesis?

Answer 11

The climate stability hypothesis assumes higher diversity in
more environmentally stable regions, tested by using a measure of temporal variance in sea surface temperature (SST)

Question 12

What is the influence of the availability of important habitat features expected to be?

Answer 12

The availability of important habitat features is expected to influence positively both abundance and richness, specifically coastline length for coastal species and frontal systems (detected as SST slopes) for oceanic species

Question 13

What do the authors expect the signatures of evolutionary history to show?

Answer 13

Some species may be more likely than others to remain in the ocean of origin. Traits such as mobility, range size and dispersal will impact upon this

Question 14

Were any hypotheses supported?

Answer 14

Sea surface temperature was the only predictor of species richness identified as statistically significant across all species groups - this lends general support to the kinetic energy /temperature hypothesis.

However:

Whereas mean richness of coastal groups other than pinnipeds tended to increase monotonically with temperature, oceanic groups on average showed an asymptotic relationship with SST, with some taxa declining in diversity at high temperatures

Question 15

were any other factors significantly related to species richness patterns?

Answer 15

all coastal groups showed significant relationships with coastline length, supporting the hypothesis that habitat area also influences species richness for these taxa.

Similarly, SST slope was significant for most oceanic taxa, indicating that oceanographic habitat features associated with steep SST gradients (fronts and eddies) mediate species richness patterns in the open ocean

Significant differences between ocean basins were detected for four coastal but no oceanic taxa, indicating a larger signature of historical geographic factors on coastal species diversity

Question 16

Are there any exceptions?

Answer 16

Pinnipeds

This is probably due to their endothermy, which represents a selective advantage in cold waters by decoupling metabolic rates from ambient temperatures

Cetaceans?

both endothermic groups (cetaceans and pinnipeds) showed stronger positive relationships with primary pro- ductivity than SST, potentially indicative of smaller constraints on activity rates but larger demands on thermoregulatory activity

Question 17

Where is human impact greatest?

Answer 17

The authors found weak but statistically significant correlations between mean anthropogenic impacts and total species richness

Hotspots for both oceanic and coastal species (defined as 90th percentile of mean normalized richness) occurred in areas with medium or higher human impact more frequently than expected by chance alone

Question 18

What are the conclusions?

Answer 18

In sum, these results indicate that temperature or kinetic energy has a consistent and dominant role in structuring broad-scale marine diversity patterns, particularly for ectothermic species, with habitat area and historical factors important for coastal taxa, and support for other factors varying by taxon.

Question 19

The authors describe total species richness as mostly being driven by fishes. Is this an appropriate way to describe the relationship between fish and species richness?

If oceanic species richness is greatest away from the equator, doesn’t this actually contradict the kinetic energy hypothesis and suggest some other factor is involved?