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 1stweek

inverse

0.035

6

0.1

0.723

Log(FGM 2ndweek)

inverse

0.8

6

16

0.016

-4.6

2.9

Log(FGM 3rd 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.

Eccard et al. BMC Ecology 2011 11:16   doi:10.1186/1472-6785-11-16

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