Table 3.

Effects of population (predation pressure), predation pressure and body size on aggressive behaviors

Source	Dependent variable	df	F	Sig.
Intercept	Spines	1	8.32	0.004
	Nips	1	2.31	0.131
	Time orienting	1	60.44	0.000
Weight	Spines	1	0.57	0.453
	Nips	1	0.20	0.659
	Time orienting	1	5.24	0.023
Population (predation pressure)	Spines	9	2.95	0.003
	Nips	9	4.91	0.000
	Time orienting	9	4.82	0.000
Predation pressure	Spines	1	1.57	0.212
	Nips	1	0.16	0.686
	Time orienting	1	0.06	0.812
Error	Spines	204
	Nips	204
	Time orienting	204

The effect of population was tested by nesting it within high or low predation pressure