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ANTEFACT
I recently read in threads of this forum as well as in older AVA threads some arbitrary and bizarre conclusions concerning the validity of the estimate (I stress the attention on the word estimate) provided by zoologists Packer and colleagues as average body mass of adult male lions of Ngorongoro Crater.
The estimate figure guilty to have caused an earthquake in recent years is 212 kg.
Packer also appeared to have provided as a personal communication chest girth range of Ngorongoro Crater lions as 1270-1340 mm without specifying sex and age class. This range is believed to refer to the adult male class
THE CRIME
On the basis of body mass vs chest girth strong correlation Packer and colleagues estimate body mass of 6 adult male lions from Ngorongoro Crater average 212 kg and 10 adult male from the Serengeti Plains average 182 kg. The adult class include animals from 6,1 to 9,8 years old (average 7.6) therefore fully grown in prime and post prime age. Note that male lions from the Serengeti came from the Plains and not from the Woodlands where prey density is higher and where lions on average appears to be slightly heavier as corroborated in part from the sample of Bertram & King (1976) mostly coming from the Woodlands (Bertram, 1978).
On the basis of body mass vs chest girth strong correlation Packer and colleagues also estimate body mass of 8 adult female lions aged 3,5 to 11 years old (average 6,9) from Ngorongoro Crater average 127 kg and that of 12 adult female lions aged 3,8 to 9 years old (average 6,5) from the Serengeti Plains average 104,3 kg. This adult class include animals in prime and past-prime age as well as sub-adults (often considered as such if 2<= age < 4 years old). Note again that female lions from the Serengeti came from the Plains and not from the Woodlands
The equation provided by U. S. Seal to Packer for males differs to the one provided for females. According to my info both equations have been obtained from regressions of lion data in the Serengeti Ecosystem but not including Ngorongoro Crater.
MY ANALYSIS
The equation for females appears to produce reasonably results and suggest, reversing the equation, average chest girth of adult female lions in Ngorongoro Crater to be 1140 mm and in the Serengeti Plains to be 1014 mm. According to my unpublished raw data from the Serengeti, from Smuts et al., 1980, summary data from East Africa (although including some unmatched individuals) and other data available from East Africa these are sensible results. However the figure of 1140 mm of average chest girth for adult female lions is undoubly a rather high value. If anything it can be noticed that the average body mass of adult females from the Serengeti is slightly underestimated from the equation as the average body mass from East Africa (therefore not only the Serengeti) with large enough sample size provide by peer-reviewed scientific publications mostly fall around 119,5 kg (Smuts et al.,1980) to 124 kg specifically for the Serengeti (Bertram & King, 1976). My unpublished raw data sample from the Serengeti of body masses matches these averages of around 120 kg well. Chest girth of 1014 mm appears very much consistent to average from Smuts et al. (1980) in East Africa while average from my homogeneous raw data sample from the Serengeti suggests a slight higher value (but it can be said is fairly well consistent too).
I do not consider the average of 151 kg from Meinertzhagen (1938) for 5 adult females supposedly randomly taken in Kenya as representative. It looks like a gross exaggeration and misrepresenting the reality of the whole East Africa population although some sub-populations in Kenya such as the one from Laikipia appear particularly large. The sample from Meinertzhagen (1938) includes 2 very large female and a huge one that I have some suspect was tagged in the paper as a female for a mistake (see my more detailed comments in another thread). However any zoologist using that sample has accepted that individual as a female and therefore I accept it as such (perhaps it was really so heavy and maybe even pregnant). On the opposite the adult male sample from Meinertzhagen (1938) lacks even a single large individual among 14 with body mass in excess of 200 kg (max 191 kg, max reported by Smuts et al., 1980, 204,7 kg among 25 individuals), which is an unusual circumstance.
I am not considering neither small samples at this stage nor any sample made up from the myriad of individual data available from literature as non-homogenous. I remind that any really meaningful sample in statistics must be at least random and homogeneous thus including in the present case small adult or unhealthy adult or very old individuals (all belonging to the same age class). These animals too represent the population at any given time and not only the healthy good size ones (I would say only clearly emaciated individuals should be excluded).
The slight underestimation of average body mass from the Serengeti Plains does not necessarily at all implicate average body mass of adult females from Ngorongoro Crater is also an underestimate although the 127 kg figure is definitely not high for adult female lions appearing to average 1140 mm in chest girth on the basis of the reverse equation (if fully correct). From my published and unpublished raw data data I would expect an average body mass of at least 140 kg and possibly even up to around 150 kg as also evident from Smuts et al. (1980) summary data.
The equation reported for males has a clear error somewhere, a typing error and not a conceptual error. The fact that the equation shown in the paper has a typo error does not implicate at all that the real equation used to get the 212 kg and 182 kg average body mass is not correct in the sense that is unable to produce sensible results. The Serengeti Plains adult male lion average body mass is very much sensible (182 kg) and consistent to results available from peer-reviewed scientific publications with proper homogeneous random sample size. These results range from ca. 175 kg (Meinertzhagen, 1938, for Kenya and Smuts et al., 1980 for East Africa) to 187 kg for the Serengeti (Bertram & King, 1976). It can be noticed the estimated average of 182 kg is within + 3,85% (+7 kg) and – 2,67%. (-5 kg) from averages calculated with actual body masses in the aforementioned samples. The average actual body mass figures of 175, 182 and 187 kg match very well the average from my homogeneous unpublished raw data of adult male lion body mass in the Serengeti.
The consistency and accuracy appearing for the estimated average Serengeti Plains male lions body mass does not at all implicate the average suggested for Ngorongoro Crater male lion is similarly accurate. The true (unknown) average could be either lower or higher then 212 kg even by a significant margin perhaps -15 kg to + 15 kg (unlikely).
What we do know is that the correct (in the sense of how it should have been printed and not in the accuracy of the prediction) regression equation predicts an average of 212 kg, that the equation shown in the paper has a typo and that Packer has provided in a personal communication a range of chest girth for lions in Ngorongoro Crater of 1270-1340 mm (supposedly referring to the adult age male class as highlighted above).
MY ESTIMATES
On the basis of the chest girth range of 1270-1340 mm provided for lions in Ngorongoro Crater by Packer and supposedly referring to the 6 male individuals of the adult age class in the paper from Brown et al. (1991) I computed the following estimates:
Likely minimum body mass range for 1270-1340 mm range of chest girth : 195-213 kg
Likely intermedium body mass range for 1270-1340 mm range of chest girth : 202-230 kg
Likely maximum body mass range for 1270-1340 mm range of chest girth : 207-243 kg
Assuming the average chest girth in the adult male sample from Ngorongoro Crater (N=6) has the same ratio to the median of the range then the average of the corresponding ratios calculated from data in Smuts et al. (1980), the average chest girth of Ngorongoro Crater adult male lions can be estimated at 101,42% of the median of the range, meaning 132,4 mm.
At this chest girth I estimate the likely range of average body mass of Ngorongoro Crater adult male lions 208-223 kg. I highlight that on statistical basis, of the 95% Confidence Interval and allometric equations, in my opinion the upper value is conservative, but good sense suggests me to rule out that we could obtain a real average higher then that from actual body masses. I also conservative consider that the average chest girth may be below the median value of the range instead of above. I am therefore keen to modify my range of average body mass statistically obtained (208-223 kg) to the rounded range of 205-220 kg.
MY CONCLUSION
Based on the chest girth range of 1270-1340 mm provided by Packer for Ngorongoro Crater lions (unknown number of individuals, unknown sex and age classes and supposed males, adults and not including sub-adults) and all the bulk of the accurate and scientifically approved published and unpublished raw data of chest girth and body masses in my possession I estimate the average body mass of Ngorongoro Crater male lions to likely fall in the range 205-220 kg.
I also estimate that a sample of adult male lions with chest girth in the range 1270-1340 mm have a likely body mass range falling within the range 195-243 kg or more conservatively 195-230 kg.
The estimate provided by Brown et al (1991) of 212 kg as average body mass for the N=6 sample of Ngorongoro Crater adult male lions is therefore perfectly included in my estimated range 205-220 kg. I therefore believe this estimate of 212 kg from Brown et al. (1991) reflects with good level of accuracy the likely average actual body mass of those 6 individuals in that sample (that will never be known) in spite of the typo in the equation appearing in their paper.
The estimate provided by Brown et al (1991) of 212 kg as average body mass for the N=6 sample of Ngorongoro Crater adult male lions cannot be discarded and, as an estimate, is very much valid.
WaveRiders
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