Vipera berus population densities

[Daniel Bohle]

ok,

the chance to find an animals is not the same over the year
its also depending on if you are looking for male, female, female reprodukitiv, subadult/juvenile.
so you need to use a big period of time, but that means that some of your animals are already dead
and dead animals in real make the population small, but while estimating a dead one make the population big.

whatever if you use a big period of time you get a big population size, if you use a smal you get a small pop size
so i can say I want 100 animals and calculate the timeperiod that big to get a pop size of 100 animals...

another point, if you found one specific animal you have a way bigger chance to find this again compared to the animals you found not.
and so on...so most of the rules for estimation are already broken or not?

im sure if you visit your area very often and you simply count what you see over the year and add the numbers you saw the year before and after, you get a number that is closer to the truth than with the common estimations.
maybe its possible with a very complicated estimation to get better result but finally who cares if you have 102 or 113 animals as long there is no rule about what type of land area you use to calculate the population densities?

[Daniel Kane]

It need not be species-specific however it would help to have a comparison for a closely-related species. I see in the Arnold & Ovenden field guide they have a figure of 1-12 (or more) animals per hectare, but no mention of how they obtained this. I suppose in an ideal world I would have the same study done an the next adder population down the road which is essentially the same habitat, but I realise I will not have this data.

You should contact David Sewell at the University of Kent, has been doing lots of research on this kind of thing lately.

http://www.kent.ac.uk/sac/staff-profiles/profiles/conservation-ecology/research-and-pt-staff/sewell_david.html

Thanks a lot for that Liam, I will be sure to drop him an e-mail.

Currently (just using the simple mrr formula of number found in first sample x number in second sample / number recaptured I have estimates of roughly between 33 and 52 adult animals. I would deem this pretty accurate going on what I have found over the years there (33 snakes id'd so far, increases every year), but of course it would be good to have comparisons to make and others who have done similar work would be valuable for references!

[Berislav Horvatic]

I am looking more for capture-recapture data, preferably on Vipera.

What one can always do with CMR data is to simply try out several estimation methods
and compare the results.
Here are the results for our V. berus bosniensis monitoring site in the vicinity of Zagreb.
The figures are population densities expressed as No of individuals/ha.

CLOSED-POPULATION METHODS:
Schnabel 4.5
Schumacher - Eschmeyer 4.1
Removal 4.2

OPEN-POPULATION METHODS:
Jolly - Seber 4.6
Fisher - Ford 5.5

The monitoring patch has an area of 12.7 ha and is certainly of an "open" type.

So, the results are not widely different and give a rough estimate of 4 - 6 individuals per hectare,
which is better than nothing. They should certainly be regarded as "preliminary", as the analysis
was made on only 50 captured individuals with 56 recaptures.

[Daniel Kane]

Berislav, that is what I'm looking for! Is that your own 'personal' data, or can I find it published anywhere?

[Berislav Horvatic]

Berislav, that is what I'm looking for! Is that your own 'personal' data, or can I find it published anywhere?

See my first posting (that everybody ignored)... So far it's my "personal" data, that is, it's all
in the unpublished MSc thesis of Igor Vilaj. For this particular data you can cite it as such,
but for more you'll have to wait for some publication of his.

Some useful literature in English:

Pradel 1996
http://www.cefe.cnrs.fr/images/stories/ ... s-1996.pdf

Jolly-Seber
http://oak.snr.missouri.edu/nr3110/topics/jolly.html

Removal
http://home.comcast.net/~sharov/PopEcol ... recap.html

[Liam Russell]

This might be useful

http://i122server.vu-wien.ac.at/pop/Flatt_website/Flatt1997.pdf

This too if you can get hold of a copy (and if it's English):
Ursenbacher et al 2003. A five year study of an adder population (Vipera berus) in the Swiss Jura mountains: number of animals and discussion of population estimate methods.
Source: Bulletin de la Société herpétologique de France. iss:107 pg:15 -25

[Berislav Horvatic]

Analysis of Marked Animal Encounter Data

Story

There was once a group of Statisticians and a group of Engineers riding together on a train to joint meetings. All the Engineers had tickets, but the Statisticians only had one ticket between them. Inquisitive by nature, the Engineers asked the Statisticians how they were going to get away with such a small sample of tickets when the conductor came through. The Statisticians said, "Easy. We have methods for dealing with that."

Later, when the conductor came to punch tickets, all the Statisticians slipped quietly into the bathroom. When the conductor knocked on the door, the head Statistician slipped their one ticket under the door thoroughly fooling the layman conductor.

After the joint meetings were over, the Statisticians and the Engineers again found themselves on the same train. Always quick to catch on, the Engineers had purchased one ticket between them. The Statisticians (always on the cutting edge) had purchased NO tickets for the trip home. Confused, the Engineers asked the Statisticians "We understand how your methods worked when you had one ticket, but how can you possibly get away with no tickets?" "Easy," replied the Statisticians smugly, "we have different methods for dealing with that situation."

Later, when the conductor was in the next car, all the Engineers trotted off to the bathroom with their one ticket and all the Statisticians packed into the other bathroom. Shortly, the head Statistician crept over to where the Engineers were hiding and knocked authoritatively on the door. As they had been instructed, the Engineers slipped their one ticket under the door. The head Statistician took the Engineers' one and only ticket and returned triumphantly to the Statistician group. Of course, the Engineers were subsequently discovered and publicly humiliated.

MORAL OF THE STORY: Do not use statistical methods unless you understand the principles behind them.

http://warnercnr.colostate.edu/~gwhite/fw663/Mark.html

[Mario Schweiger]

I think, thats exactly, what you are looking for - but in German language.
Schwarz, A. 1997. Möglichkeiten der Ermittlung von Raumnutzung und Populationsdichte bei der Kreuzotter (Vipera b. berus L.). In: K. HENLE & M. VEITH (Hrsg.): Naturschutzrelevante Methoden der Feldherpetologie - Mertensiella 7: 247-260.
Its PDF-4477 in the database
Summary:
Methods of determining home ranges, habitat size, and population density in a population of the adder (Vipera b. berus L.).
A population of the adder was studied for one year. The study area had a total size of 370 ha and was isolated from other adder habitats. It could be shown that the use of standard methods for estimating home ranges of individual snakes, such as the convex-polygon method, is problematic in cases of few observations in a heterogeneous study area. Male adders migrated up to 1200 m, females up to 935 m. However, no clear spacial separation between seasonally used habitats, such as hibernating sites, basking sites, mating/breeding sites, and summer grounds, could be found. Using three different mark-recapture methods the population size was estimated to be about 57-97 adult individuals with a sex ratio of almost 1:1. For the 45 ha area actually used by the snakes, a population density of 1.3 - 2.2 adult individuals/ha was calculated.

The estimated values for density, made with JOLLY (57) as well as with SCHNABEL (72) gave lower values than the effective number of individuals (81) !!!

Mario

[Jeroen Speybroeck]

This too if you can get hold of a copy (and if it's English):
Ursenbacher et al 2003. A five year study of an adder population (Vipera berus) in the Swiss Jura mountains: number of animals and discussion of population estimate methods.
Source: Bulletin de la Société herpétologique de France. iss:107 pg:15 -25

It's not in English, but in French. They use more or less the same methods as listed by Bero.

Here's the English abstract. I will mail the entire paper to Mario.

[Jeroen Speybroeck]

Bero, you can show us that you understand the principles behind CMR by adding a measure of deviance to each n°/ha.