Managing Kruger s Elephants: the Metapopulation Metaphor

Transcription

1 Managing Kruger s Elephants: the Metapopulation Metaphor Rudi van Aarde, Sam Ferreira, Tim Jackson & Adrian Shrader Supported by postgraduate students Conservation Ecology Research Unit University of Pretoria South Africa Rudi van Aarde

2 Supporting agencies (2003 to 2005) Bateleurs Botswana Dept. Wildlife & National Parks Conservation International Conservation Fund Zambia Conservation Lower Zambezi Direcção Nacional de Areas de Conservação, Mozambique International Fund for Animal Welfare Kalahari Conservation Society Mozal Community Development Trust National Research Foundation Namibian Min. Tourism & Environment National Postcode Lottery, Netherlands Malawian Wildlife Department Peace Parks Foundation South African National Parks US Fish & Wildlife Services University of Pretoria WWF South Africa Zambian Wildlife Authority

3 Conservation management of elephants Urgent but controversial. Driven by personal opinion and experience. Often motivated by selective interpretation of information. Conservation measures for ex situ and in situ populations differ.

4 Immigration Births Population Deaths Emigration

5 Immigration Transfrontier parks Contraception Culling Births Population Deaths Transfrontier parks Emigration

6 Births Immigration Metapopulation Metapopulation Population Metapopulation Metapopulation Emigration Deaths

7 The Metapopulation Approach A collection of populations of the same species. Dynamics of these populations are asynchronous. Dispersal occurs between populations.

8 Time (t) Time (t + 1)

9 Angola Zambia Malawi Mozambique Zimbabwe Namibia Botswana South Africa

10 Linear Spatial Model 0.5d i 0.5d i N i-1 N i N i+1 0.5d i-1 b i m i 0.5d i+1 N i, t+ 1 = Ni, t + 0.5di 1Ni 1, t 0.5di Ni, t + bi Ni, t mi Ni, t 0.5di Ni, t di+ 1Ni+ 1, t N n j, i i, t+ 1 = Ni, t + bi Ni mi Ni + N j j= 1 n d d i N i

11 Time (Years) Density (n.km -2 ) Regional Density (n.km -2 )

12 The benefits of the metapopulation approach Allows for the natural limitation of populations regionally. Provides opportunity for habitat regeneration. Provides regional conservation management opportunities.

13 Kruger s elephants as a metapopulation? Avoid the asymptote syndrome. Need an uneven distribution and density of elephants. Vacant habitats available. Maintain natural forces limiting numbers. Metapopulation dynamics needs space and time. Map provided by SANParks

14 Kruger s elephants as a metapopulation? Avoid the asymptote syndrome. Need an uneven distribution and density of elephants. Vacant habitats available. Maintain natural forces limiting numbers. Metapopulation dynamics needs space and time. Map modified from Whyte 2004

15 Response to culling population growth rate Years after culling From:- Van Aarde et al. 1999, Animal Conservation 2,

16 Range use in Kruger 95% MCP for 48 elephant cows ( ) From Grainger, 2003 MSc thesis, UP Rudi van Aarde

17 Home range areas for elephants across Kruger National Park Home range size (km 2 ) n= Artificial water resource richness density (number per 100km 2 ) From Grainger, van Aarde & Whyte (accepted)

18 Population numbers - Kruger National Park - Number of elephants Culling Year Van Aarde et al. 1999, Animal Conservation 2, Whyte et al The Kruger experience Tim Jackson

19 Population variables - Kruger National Park Variable Onset of culling era ( )* Late culling era ( )* Post culling era (2004) Calving interval 4.01± ± ±0.09 First calving 12.41± ± ±0.26 Survival (calves) 0.983± ± ±0.005 S 2-4 (Young) 0.983± ± ±0.003 ** Raw data from Ian Whyte, SAN Parks (in litt.) All values followed by one S.E. of the mean From Ferreira & van Aarde in prep.

20 Population trend in Kruger National Park ( ) Number of elephants r=1.13±0.34% r=3.85±0.85% Year r=11.2±0.02% Data from Ian Whyte, SAN Parks (in litt.) Rudi van Aarde

21 Age at first calving Ferreira, Shrader & van Aarde in prep. Young Short High Rudi van Aarde Etosha Okavango Moremi Chobe Kafue L. Zambesi Vwaza Kruger Tembe Maputo Addo Calving interval Etosha Okavango Moremi Chobe Kafue L. Zambesi Vwaza Kruger Tembe Maputo Addo Calves surviving (prob) Etosha Okavango Moremi Chobe Kafue L. Zambesi Vwaza Kruger Tembe Maputo Addo 0.00

22 Yearly Intrinsic Population Growth Rate - Southern African Elephants Intrinsic population growth rate Etosha Okavango Moremi Chobe Kafue L. Zambesi Vwaza Kruger Tembe Maputo Addo From Ferreira, Shrader & van Aarde in prep.

23 How do we overcome the problem? Allow survival and reproduction to be limited. Stop tampering with resources that limit populations. Restore population limitation through metapopulation dynamics. Rudi van Aarde

24 Angola Zambia Malawi Mozambique Zimbabwe Namibia Botswana South Africa

25 When there is little evidence available, doing nothing might sometimes be the best worst option, however politically unacceptable this might seem. Griffiths, R.A. (November 2004). Trends in Ecology and Evolution 19:

26

27 Geo-political delineation of TFCA across southern Africa