Reilly and Fiedler: Interannual variability of dolphin habitats 



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P-value < 0.001. The same was true 

 for the first axis alone; no random 

 permutation had an eigenvalue 

 larger than the observed 0.309, 

 again giving a P-value < 0.001. 

 These results indicate that the prob- 

 ability of a Type-I error is less than 

 0.1%. (The CCA program, CAN- 

 OCO, provided this test only for the 

 trace and first axis, so no test was 

 done for subsequent axes). 



The species-environment biplot 

 (Fig. 5A) displays the results for the 

 six variable 'oceanographic' ordina- 

 tion. Fig. 5B shows the ordination 

 with species tolerances, but without 

 the visual distraction of the environ- 

 mental vectors. The first axis sepa- 

 rates common dolphins from all 

 school types containing spotted and 

 spinner dolphins. Positive scores on 

 axis 1 are associated with cooler 

 temperature (r=-0.88, Table 3), a 

 thermocline that is shallower (i.e. 

 smaller Z20, r=-0.70), yet weaker 

 (larger difference in depth between 

 20° and 15°C isotherms, r =+0.45), 

 denser surface water (higher sigma- 

 t, r=+0.61) and high chlorophyll 

 (r=+0.49). These are characteristics 

 of "cool upwelling" habitat, as found 

 in Equatorial and Peru/California 

 Current surface waters. The dis- 

 tinct placement of common dolphins 

 in the positive region of this axis 

 indicates this is their preferred 

 habitat. Negative scores on axis 1 

 are associated with warm tempera- 

 ture, a deeper and stronger ther- 

 mocline, and lower chlorophyll, as 

 found in less productive Tropical 

 Surface Water. The placement of all 

 spotted and spinner school types in 

 the negative region indicates that 

 these oceanographic conditions help 

 define their preferred habitats. 



Site or species scores on axis 2 are 

 uncorrelated with scores on axis 1, 

 by definition. Positive axis-2 scores 

 are associated with a relatively 

 shallow thermocline (r=-0.63, Table 

 3 ) and high chlorophyll (r=+0.40) as 

 for axis 1, but also with warmer 

 temperatures and lower salinity 

 (lower sigma-t) rather than cool 



