Loss of density-dependence and incomplete control by dominant breeders in a territorial species with density outbreaks

Table 2 Regression models for the effect of density (number of females per enclosure) on variables of reproduction, space use and physiology in enclosure experiments on bank voles.

study	variable	model	R2	n	F	p	coefficient a	constant b
moderate densities (4-20 bank vole females/ha)
	breeding females	inverse	0.230	38	12.1	0.001	-3.37	3.78
	breeding females	linear	0.265	38	14.3	0.001	0.43	1.1
moderate to high densities (12-42 bank vole females/ha)
	breeding females	linear	0.817	12	50.2	< 0.001	0.83	-2.33
	breeding females	inverse	0.674	12	23.7	0.001	-70.6	14.2
	mean litter size	linear	< 0.01	12	< 0.01	0.931
	mean home range	inverse	0.789	12	37.5	< 0.001	2420	364
	interaction (nr. of females)	linear	0.653	12	18.9	0.001	0.45	0.58
	captures/animal	linear	0.3	12	4.2	0.065	-0.21	8.7
	Log(FGM 1^stweek	inverse	0.035	6	0.1	0.723
	Log(FGM 2^ndweek)	inverse	0.8	6	16	0.016	-4.6	2.9
	Log(FGM 3^rd week)	inverse	0.562	6	5.1	0.086

We tested linear model (y = ax+b) and/or an inverse models (y = a/x+b), the latter indicating a threshold value (constant b) for high densities. Analyses were based on populations (rates or enclosure means). 38 Populations at moderate densities were investigated over 4 years in different earlier experiments (see text), 12 populations in moderate to high densities were investigated during the 2-year experiment reported here.

ISSN: 1472-6785