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ASSOCIATION BETWEEN ROE DEER AND LYNX ABUNDANCE IN LATVIA
Janis Baumanis1, Aivars Omicans2, Alda Stepanova2 & Janis Ozolins2
Latvia University of Agriculture, Jelgava, Latvia, [email protected] 2Latvian State Forest Research Institute "Silava", Salaspils, Latvia, [email protected]
Roe deer Capreolus capreolus is an abundant and popular game species in Latvia. Population met a fast increase during the first decade of 21st century after a deep depression around middle 1990-s. The main predator of the roe deer is Eurasian lynx Lynx lynx whose population dynamics appeared following this increase (Zun-na et al. 2011). Furthermore, management of lynx population has changed crucially in 2004 when the carnivore got under protection by European Council's Species and Habitat directive 92/43/EEC. Lynx harvest was restricted significantly so its population increased due to both prey abundance and diminished mortality. Meanwhile, the habitat and climatic conditions that depend on distance from the Baltic Sea coast as well as on north - south gradient, affect the roe deer within territory of Latvia to a different extent. Our study includes a period from 2002 to 2010 and our aim was to contribute to the knowledge of prey - predator relationship in these two species in terms of population reproduction and dynamics.
Statistics on numbers of estimated and harvested game species were used. Hunters had filled in special forms attached to each shooting permit so that data on roe deer were well structured in sex and age classes enabling researchers to follow the trends in fawn and male-to-female ratio. Lynx bags were examined by researchers on random basis since the hunters made mistakes about kitten gender too often. Carcasses of adult female lynx were investigated for placental scars. Age was determined by checking one of the canines and, in adult individuals, by counting incremental lines of the tooth cement microscopically as described by Klevezal (KneBe3anb 1988). All data were pooled into four groups according habitat conditions and actual status of lynx and roe deer populations in various districts:
Group 1 merges districts with most favourable climate for roe deer but a scarce lynx population (rough guided -in south-west of Latvia).
Group 2 is selected for districts with comparatively severe climate for roe deer but a dense lynx population, even documented as local core areas for lynx over the centuries (north-west and north-east of Latvia).
Group 3 is central part of Latvia from very south to north with average climate conditions whilst roe deer and lynx populations always were comparatively abundant. Group 4 is related to districts with most continental climate, lowest density of roe deer and a scarce lynx population too (east and south-east of Latvia).
On average, from 2002 to 2009 abundance of roe deer in Latvia increased from 12 to 34 individuals per 1000ha according estimates, and from 2 to 5 shot individuals per 1000ha according the hunting bags (Fig.1) that means nearly threefold increase. Decline noticed in 2010 was because of very snowy winter 2009/2010. The lynx increased respectively as well, however just twofold. Lynx harvest has stabilised at 2 animals per 1000km2. Such hunting pressure enables population recruitment satisfying conservation aims and population might even grow. Another index confirming that growing lynx population not necessarily impacts roe deer dynamics while winters were favourable is juvenile ratio in hunting bags (Table 1.).
Fig.1. Changes in lynx and roe deer abundance according estimate (left) and harvest data (right) from 2002 to 2010 in Latvia. Hunting lasts from 1st June to 30th Nov. for roe deer and from 1st Oct. (2002), 1st Nov. (2003) or 1st Dec. (2004) to 31st March for the lynx. Estimates are reported annually by April 1 (source - the State Forest Service of Latvia: www.vmd.gov.lv).
Percentage of fawns in the hunting bags of roe deer increased twofold that is undoubtedly in line with total increase of roe deer population. Fawn ratio is slightly higher in the districts with more favourable conditions and less lynx density but generally the increase was observed throughout the country until winter 2009/2010. Meanwhile, the males even surprisingly dominated over females. It could be also related to compensatory reproduction probably caused by selective over-harvest of particularly males in matured age classes. After severe winter of 2009/2010, buck shooting for trophies was deliberately reduced and predominance of male fawns likely stopped. Kitten ratio in lynx sample (n=375) fluctuated within limits from 25,0% to
51,2%. So did the ratio between males and females of lynx kittens (Tab.1), while in total sample it did not deviate significantly from 1:1 (716'6', 75??). Particularly little number of lynx kittens had been taken in districts with low lynx density (Group 4), however adult females from this territory had the highest index of fecundity - 3,38±0,52 placental scars. A gap between number of placental scars and that of kittens or yearlings could mean an elevated postnatal mortality. Lynx fecundity was 3,00±0,80 in Group 1, 3,03±0,39 in Group 2 and 2,86±0,45 in Group 3. Generally, however, we did not find any significant difference among number of placental scars in lynx females from the four territorial groups (Mann-Whitney U test).
Most interesting results were found comparing population densities in lynx and roe deer from the four territorial groups by regression analysis (Fig.2). In Group 1, 3 and 4, despite of different initial lynx densities and habitat conditions, the predator was similarly associated with abundance of its prey.
In Group 2, a higher density of lynx population was more noticeably related with a higher abundance of roe deer. These are districts where lynx never became extinct even in 20th century when population dropped down to a minimum (Andersone et al. 2003). Results suggest at least two conclusions.
First, whilst other conditions are favourable, roe deer in Latvia does not suffer much from lynx increase. In general, more roe deer is associated with more lynx, however we could not observe in this study whether abundant roe deer caused better reproduction in lynx.
Second, in increase stage of both prey and predator populations, lynx reaction to prey abundance was more pronounced just in core areas of local range where the predator had better survival during periods of depression.
REFERENCES
Andersone, Z., Ozolins, J., Pupila, A. and Bagrade, G. 2003. The East European and Caucasian parts of lynx range (the western group of regions): Latvia. In: Matyushkin, Y.N. and Vaisfeld, M.A. (eds.), The Lynx: Regional Features of Ecology, Use and Protection. Moscow: Nauka, Р. 92 - 105. (in Russian)
Zunna, A., Ozolins, J., Stepanova, A., Ornicans, A., Bagrade, G. (2011). Food habits of the lynx (Lynx lynx) in Latvia based on hunting data. - In: M. Stubbe (ed.), Beitrage zur Jagd- und Wildforschung, Band 36, Halle/Saale: Gesellschaft fQr Wildtierb- und Jagdforschung e.V., S. 309-317.
Клевезаль Г. А. Регистрирующие структуры млекопитающих в зоологических исследованиях. M. : HayKa, 1988.
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Fig.2. Regression between estimated lynx and roe deer numbers over period from 2002 to 2010 in four study areas with various climate and habitat conditions. Graph 1 - districts with good conditions for roe deer and a poor lynx population; graph 2 - districts bad for roe deer and a good lynx population; graph 3 - districts comparatively good for both species; graph 4 - districts bad for both species.
Table 1
Indices of lynx and roe deer reproduction in samples from hunting bags
Reproduction indices 2002 2003 2004 2005 2006 2007 2008 2009 2010
Ratio of roe deer fawns(%) 12,2 18,7 19,7 20,6 20,6 23,0 23,6 24,2 21,6
Males/females in fawns* 1,43 1,83 1,84 1,27 1,17 1,17 1,19 1,10 0,95
Ratio of lynx kittens(%) 39,1 25,0 34,4 44,7 40,5 51,2 40,0 36,5 33,3
Males/females in kittens** 2,00 - 0,57 0,89 1,43 0,83 1,17 0,73 1,22
Number of placental scars in 2,75 2,50 3,67 3,00 2,75 2,67 3,05 3,50 3,00
fertile lynx females ±1,23 ±0,98 ±0,65 ±0,46 ±0,81 ±1,10 ±0,44 ±1,10 ±0,74
Ratio of lynx yearlings(%) 17,4 20,0 9,4 0 0 0 3,1 9,6 5,0
2
1
3
4
* significant (P=0,01) male dominance from 2002 to 2009 according x2 test; ** insignificant difference due to small sample size
