Natural Prey Preferences and Spatial Variability of Predation Pressure by Cyphoma gibbosum (Mollusca: Gastropoda) on Octocoral Communities off La Parguera, Puerto Rico

Table 3

Ivlev’s prey electivity index for each reef zone for octocoral species harboring snails. Prey electivity , was estimated whereby is the proportion of prey species utilized and is the proportion of prey species available.

Inner reefs	Occupancy		Availability		Electivity index
Octocoral spp.						Spp. utilization
B. asbestinum	0	0.000	25	0.019	−1.000	Total rejection
G. ventalina	10	0.156	370	0.280	−0.284	Total rejection
P. americana	33	0.516	496	0.375	0.158	Prop. abundance
P. acerosa	4	0.063	141	0.107	−0.259	Total rejection
P. flexuosa	8	0.125	154	0.117	0.033	Prop. abundance
P. porosa	8	0.125	101	0.076	0.244	Prop. abundance
P. homomalla	1	0.016	34	0.026	−0.238	Total rejection
Total	64	1.0	1321	1.0
Mid-shelf reefs	Occupancy		Availability		Electivity index
Octocoral spp.						Spp. utilization
B. asbestinum	5	0.125	58	0.040	0.515	Prop. abundance
G. ventalina	9	0.225	470	0.327	0.185	Prop. abundance
P. americana	10	0.250	255	0.177	0.171	Prop. abundance
P. acerosa	0	0.000	194	0.135	−1.000	Total rejection
P. flexuosa	10	0.250	250	0.174	0.179	Prop. abundance
P. porosa	3	0.075	182	0.127	−0.257	Total rejection
P. homomalla	3	0.075	28	0.019	0.596	Prop. abundance
Total	40	1.0	1437	1.0
Shelf-Edge Reefs	Occupancy		Availability		Electivity index
Octocoral spp.						Spp. utilization
B. asbestinum	11	0.105	47	0.059	0.280	Prop. abundance
G. ventalina	48	0.457	313	0.393	0.075	Prop. abundance
P. americana	18	0.171	76	0.095	0.286	Prop. abundance
P. acerosa	2	0.019	62	0.078	0.603	Prop. abundance
P. flexuosa	16	0.152	128	0.161	−0.029	Total rejection
P. porosa	10	0.095	142	0.178	−0.304	Total rejection
P. homomalla	0	0.000	28	0.035	−1.000	Total rejection
Total	105	1.0	796	1.0