Hp. Andreassen et Ra. Ims, The effects of experimental habitat destruction and patch isolation on space use and fitness parameters in female root vole Microtus oeconomus, J ANIM ECOL, 67(6), 1998, pp. 941-952
1. The aim of this study was to test whether experimentally induced destruc
tion and fragmentation of habitat and varying degrees of patch isolation ap
plied to 11 experimental populations of root voles affected space use and f
itness parameters in radio-tracked females. It was predicted that the habit
at destruction would disrupt the spatiosocial relations between breeding in
dividuals, which, in turn, would cause lowered survival and reproductive su
ccess. Different degrees of patch isolation were expected to affect the rat
e of risky and energetically costly interpatch movements.
2. The experimental habitat destruction comprised the removal of more than
half of the habitat area (meadow vegetation) in each of seven populations t
hat had been established in a large continuous habitat block. This treatmen
t yielded six small, habitat patches arranged in two clusters with long and
short interfragment distances, respectively. Measures of individual space
use, survival rates (predation and unknown causes) and litter production we
re contrasted with equivalent measures obtained from four control populatio
ns. The control populations had been established in permanently fragmented
plots with the same fragment configuration as the post-destruction treatmen
t populations. The effect of different interpatch distance was tested by co
mparing movement rates, space use and demographic parameters between the tw
o types of patch cluster.
3. Home ranges were larger in the continuous predestruction populations com
pared to the permanently fragmented control populations. There was a large
decrease in home range area of individual females as a result of habitat de
struction, and they became temporally smaller than in the control plots. Th
e degree of overlap only increased on home range core areas. The degree of
space sharing between matrilineal related females, a main characteristic of
Microtus social organization, was higher in the permanently fragmented pop
ulations (controls) than in the treatment populations. This difference was
also maintained after habitat destruction. Thus, the basic spatiosocial org
anization of reproductive females when first established, seems to be very
resistant to habitat destruction. There were no effects of habitat destruct
ion on female fitness parameters when tested for either at the cluster or t
he population level.
4. There were less between-patch movements when interpatch distances were l
arge than when they were small, irrespective of the fragmentation history o
f the population. Predation by avian predators, the main mortality cause, w
as highest in fragment clusters with long interpatch distances, probably be
cause long distance movements between fragments increased the predation ris
k.
5. There was a large intrapopulation variation with respect to how severely
individuals were affected by the habitat destruction. The farther a female
had to relocate her home range because of habitat destruction, the higher
was the predation risk. Thus, this study predicts that the most influential
aspect of habitat fragmentation on demography may be that causing long int
erpatch movements.