Ecological Archives E096-191-A3

G. P. Hempson, A. W. Illius, H. H. Hendricks, W. J. Bond, and S. Vetter. 2015. Herbivore population regulation and resource heterogeneity in a stochastic environment. Ecology 96:21702180. http://dx.doi.org/10.1890/14-1501.1

Appendix C. Body mass model structure and parameter estimates.

Body mass (kg) was modeled to determine the effect of individual status and environmental conditions on goat body condition. Age2 (months), reproductive status (five level factor: ‘early pregnant’, ‘pregnant’, ‘lactating’, ‘not pregnant’ or ‘unknown’) and the interaction between these variables were fitted as fixed effects to account for the effect of individual state on body mass. Goat density (animals∙ha-1) in the preceding four weeks, season (two level factor: ‘wet season and early to mid-dry season’ or ‘mid- to late-dry season’), year (three level factor: ‘2007’, ‘2008’ or ‘2009’) and the full set of interactions among these variables were fitted as fixed effects to determine the effect of environmental conditions on body mass. The season variable breaks the seasonal cycle into two periods where forage availability is predicted a priori to be either adequate or potentially limiting. Year was fitted to account for interannual variation in forage availability, for example arising due to differences in rainfall, dry season duration or the extent of Orange River flooding. Herd and individual identities were fitted as random effects to account for repeat measures at these levels.

R model structure:

lmer(Mass ~ poly(Age,2,raw=TRUE) * Reproductive.status + Season * Year * Density + (1|Herd) + (1|Individual))

Table C1. Parameter estimates for the goat body mass model. Statistical support for parameter estimates is indicated as follows: *** p < 0.001; ** p < 0.01; * p < 0.05; p < 0.01.

 

Body mass

 

 

 

Fixed effects

 

 

Constant

18.310 (1.945)

***

 

 

 

Age2

 

 

   Age 1

13.319 (0.451)

***

   Age 2

-1.245 (0.064)

***

 

 

 

Reproductive status

 

 

   Early pregnant

 

 

   Pregnant

2.312 (0.852)

**

   Lactating

1.008 (0.830)

 

   Not pregnant

-7.417 (0.651)

***

   Unknown

-0.516 (4.518)

 

 

 

 

Season

 

 

   Wet and early to mid-dry season

 

 

   Mid- to late dry season

3.034 (0.760)

***

 

 

 

Year

 

 

   2007

 

 

   2008

2.069 (0.895)

*

   2009

2.024 (0.620)

**

 

 

 

Density

 

 

   Animals ha-1

18.549 (2.986)

***

 

 

 

Age2 × Reproductive status

 

 

   Age 1:Early pregnant

 

 

   Age 1:Pregnant

1.051 (0.552)

.

   Age 1:Lactating

-2.383 (0.514)

***

   Age 1:Not pregnant

3.296 (0.452)

***

   Age 1:Unknown

-0.667 (3.825)

 

   Age 2:Early pregnant

 

 

   Age 2:Pregnant

-0.090 (0.077)

 

   Age 2:Lactating

0.339 (0.070)

***

   Age 2:Not pregnant

-0.326 (0.066)

***

   Age 2:Unknown

0.330 (0.685)

 

 

 

 

Year × Season

 

 

   2007:Mid- to late dry season

 

 

   2008:Mid- to late dry season

-2.443 (1.132)

*

   2009:Mid- to late dry season

-3.789 (1.013)

***

 

 

 

Density × Season

 

 

   Density:Mid- to late dry season

-20.382 (5.481)

***

 

 

 

Year × Density

 

 

   2007:Density

 

 

   2008:Density

-12.334 (6.891)

.

   2009:Density

-27.396 (4.004)

***

 

 

 

Year × Density × Season

 

 

   2007:Density:Mid- to late dry season

 

 

   2008:Density:Mid- to late dry season

7.339 (8.493)

 

   2009:Density:Mid- to late dry season

16.033 (6.932)

*

 

 

 

Random effects

 

 

   Individual

16.224

 

   Herd

3.922

 

   Residual

11.319

 


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