Lynx population dynamics in relation to prey supply and diet (Paazierrie Forest)

Between 1985 and 2010, lynx population dynamics were studied in relation to prey supply (abundance of hares, Tetraonids and roe deer) and lynx diet in Paazierrie Forest (northern Belarus).

Lynx, hare and roe deer abundance was determined by counting trails crossing two census routes (36 and 44 km), 3-5 days after snowfall. Tetraonids (black grouse, capercaillie and hazel grouse) were counted by means of visual observation along the census routes.

figuur 1

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figuur 2

Lynx scats were collected year round for dietary analysis. Diet was investigated for separate periods with different prey supply:

1985-1996: low density of roe deer, fairly high density of Tetraonids and hares

Figuur 3

 

1997-2004: roe deer density increased markedly, Tetraonid density declined, hare density remained stable

Figuur4

2009-2010: low density of all main prey species, i.e. roe deer, Tetraonids and hares

Figuur 4

The data on lynx diet showed that roe deer are preferred over hares. Regardless of stability in the hare populations in 1985-2004, their share in consumed biomass in lynx diet dropped 1.4 times during the period of high roe deer density. At the same time the proportion of roe deer in prey biomass consumed by lynx increased 3.5 fold.

When all main lynx prey were scarce in 2009-2010, lynxes displayed a diversified diet. Wild boar and beaver became the most important prey species. Several species of medium sized predators (red fox, raccoon dog, pine marten) and rodents became important prey items as well.

P1000606
Pine marten predated by lynx

Prey supply not only determined the diet of the lynx, it also had a clear impact on lynx population dynamics. By comparing the changes in lynx abundance with the variations in abundance of the main prey, a positive correlation of lynx abundance with roe deer abundance was found (rs=0.90, P<0.001). Monitoring of lynx abundance showed a statistically significant increase of its population since the mid 1990’s until 2005 (rs=0.92, P<0.001). In 2006-2010, lynx abundance decreased markedly, and this change coincided with the sharp decline in roe deer abundance.

Figuur 5

 

Moreover, we investigated reproduction parameters to understand the impact of changing prey supply on lynx population dynamics.

1985-1996:

  • 2.6 kits per mother lynx and 39% of juveniles in early winter
  • 1.2 kits per mother lynx and 22% of juveniles in late winter
  • Kit mortality in winter 53.8%

1997-2005:

  • 2.2 kits per mother lynx and 34% of juveniles in early winter
  • 1.8 kits per mother lynx and 29% of juveniles in late winter
  • Kit mortality in winter 18.2%

For the main study period (1985-2005) we found a clear effect of changing prey supply on kit mortality during winter. A growing supply of roe deer after 1997 drastically improved winter survival of kits, explaining the lynx population growth.

Towards the end of the 2000’s lynxes were faced with abnormal prey supply: main lynx prey were scarce, but wild boars and beavers were common. At the beginning of winter 2009-2010 there were 2.3 kits per mother lynx. So, abnormal prey supply had no apparent effect on fecundity.  Surprisingly, kit mortality during this winter was very low (14%), similar to kit mortality during the period with abundant roe deer (1996-2005) and well below kit mortality during the period with abundant hares and Tetraonids (1985-1996).

So, how the explain the drop in lynx numbers? We registered four cases of subadult lynxes starved to death. These second year lynxes are already separated from their mother and have to survive the winter alone for the first time. It seems that these inexperienced subadults were not able to hunt efficiently on alternative prey in winter. Perhaps this inability of subadult lynxes to hunt alternative prey caused an unusually high winter mortality. Because kit mortality remained low, this winter mortality of subadults might explain the lynx population decline in 2006-2010.

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