Vipera berus population densities

[Jeroen Speybroeck]

I have estimates of roughly between 33 and 52 adult animals.

Is that a confidence interval? Not bad, I'd say...

[Jeroen Speybroeck]

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.

I would imagine you can account/standardise for those.
For one, if you say that looking for males works differently than for females, than you should balance and standardise your methodology first. Opportunistic random sampling with variable sampling effort is not the way you want to go. Unfortunately, a lot of people 'monitor' like that.

Daniel B., I don't understand all of what you wrote, but you can account for open populations (in time and space).

so i can say I want 100 animals and calculate the timeperiod that big to get a pop size of 100 animals...

? ? ?
What's the math here? Please give us an example.

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.

Benedikt Schmidt and colleagues have written interesting stuff about detectability, although more for amphibs...

Pellet, J.; Schmidt, B.R. 2005 Monitoring distributions using call surveys: estimating site occupancy, detection probabilities and inferring absence Biological Conservation 123: 27–35
Schmidt, B.R.; Feldmann, R.; Schaub, M. 2005 Demographic processes underlying population growth and decline in Salamandra salamandra Conservation Biology 19(4): 1149-1156
Sztatecsny, M.; Jehle, R.; Schmidt, B.R.; Arntzen, J.W. 2004 The abundance of premetamorphic newts (Triturus cristatus, T. marmoratus) as a function of habitat determinants: an a priori model selection approach Herpetological Journal 14: 89-97
Schmidt, B.R. 2004 Declining amphibian populations: the pitfalls of count data in the study of diversity, distributions, dynamics, and demography Herpetological Journal 14: 167-174
Indermaur, L.; Schmidt, B.R. 2011 Quantitative recommendations for amphibian terrestrial habitat conservation derived from habitat selection behavior Ecological Applications 21(7): 2548-2554
Geiger, CC; Kupfer, E; Schar, S; Wolf, S; Schmidt, BR 2011 Elevated temperature clears chytrid fungus infections from tadpoles of the midwife toad, Alytes obstetricans AMPHIBIA-REPTILIA 32 (2): 276-280
Tobler, U; Borgula, A; Schmidt, BR 2012 Populations of a Susceptible Amphibian Species Can Grow despite the Presence of a Pathogenic Chytrid Fungus PLOS ONE, 7 (4):10.1371/journal.pone.0034667 APR 5 2012
Lotters, S; Kielgast, J; Sztatecsny, M; Wagner, N; Schulte, U; Werner, P; Rodder, D; Dambach, J; Reissner, T; Hochkirch, A; Schmidt, BR 2012 Absence of infection with the amphibian chytrid fungus in the terrestrial Alpine salamander, Salamandra atra SALAMANDRA, 48 (1):58-62
Schmidt, BR; Hodl, W; Schaub, M 2012 From metamorphosis to maturity in complex life cycles: equal performance of different juvenile life history pathways ECOLOGY, 93 (3):657-667

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.

??? That's exactly taking a big leap on the issue of detectability...

as long there is no rule about what type of land area you use to calculate the population densities?

Why do you need habitat use assumptions? You just want to estimate population size for a given spot, right? If so, I would think that the spot by definition includes its particular set of habitats and their spatial distribution. If you want to differentiate between habitat types, I would propose to set up monitoring transects in each type or take the relative presences of each type in your current transects into account (stratified sampling).

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

That would mean you cannot use the removal method, imho.


I have been playing with ...
Schwarz, C. J., and A. N. Arnason. 1996. A general methodology for the analysis of capture-recapture experiments in open populations. Biometrics 52:860-873.
... for my fire salamanders, but so far, only very big variance (e.g. 95% confidence interval from 75 to 373 on one subset, 685-5618 on another........).

[Jeroen Speybroeck]

There's also a book about all this, but Bero, Liam provided useful links.
http://www.amazon.com/Handbook-Capture- ... 069108968X

[Jeroen Speybroeck]

I believe this is the opening chapter of that book...

http://press.princeton.edu/chapters/s8109.pdf

[Mario Schweiger]

Ursenbacher is online => PDF-4478 in DB

Mario

[Berislav Horvatic]

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

No, I can't.
I do not pretend to be either a biologist or a statistician, I just liked the joke and wanted to share it.
Also, it was not my work, so I can't (shouldn't) deal other people's unpublished results around. I just
wanted to help Daniel a little bit.

[Jeroen Speybroeck]

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

No, I can't.
I do not pretend to be either a biologist or a statistician, I just liked the joke and wanted to share it.
Also, it was not my work, so I can't (shouldn't) deal other people's unpublished results around. I just
wanted to help Daniel a little bit.

Is that thesis not a public document? I don't see why you would think it's OK to cite population size estimates, but giving us their accompanying confidence/variance would be a violation of unpublished data...

[Berislav Horvatic]

Is that thesis not a public document? I don't see why you would think it's OK to cite population size estimates, but giving us their accompanying confidence/variance would be a violation of unpublished data...

I consulted the author and he kindly asked me to stop at that, until he produces a proper publication.
It has nothing to do with hiding data on this particular issue you mentioned. He asked me that BEFORE
you did.
(BTW, a thesis like that is, effectively, a half-public document, and you know it. Its effective availability
depends on the regulations/customs of a particular country and/or university.)

[Jeroen Speybroeck]

I think all Belgian MSc thesis in biology are publicly available documents. Please do not make assumptions on what I do and do not know.

It's no big issue, Bero. You provided some numbers which seem to demonstrate that there's a fairly good disagreement between the different methods. Looks nice. I just think one should never consider population size estimates without some sort of deviance/variance/confidence interval indication - the values by themselves can be misleading (in relation to their error bars). You are entitled to whatever reason to disclose or not to disclose any of it, of course. Do plans exist for this thesis to result in published papers?

On a side note, how do you deal with sensitive nature of studied populations? I hear more often that editors seem to insist on providing precise coordinates...

[Daniel Bohle]

Opportunistic random sampling with variable sampling effort is not the way you want to go. Unfortunately, a lot of people 'monitor' like that.

What do you mean?

Daniel B., I don't understand all of what you wrote, ...

Yes, that's possible. I'm sorry ... it's too complex for my english skills!

... but you can account for open populations (in time and space).
...

so i can say I want 100 animals and calculate the timeperiod that big to get a pop size of 100 animals...

? ? ?
What's the math here? Please give us an example.

Last winter I tried to estimate the population size. I read a lot of papers of other people who did it and tried to understand what they did and how they did it.
one problem was that i had the feeling that people did the same method different and some even definitly wrong.
the other problem was that my estimated numbers had nothing to do with what I saw with my own eyes and some of the papers wrote the same
in general they saw more than they estimated.

so due to my huge amount of observations and fielddays combined with my "analog" way of collecting the data it would take month to make full estimation with different intervalls.
so I started to estimate just a small subopoulation and while doing this I realized that if I raise the intervall the population size is getting bigger.
in real if you have 100 animals and 10 of them are dead at the end of they year you simply have 90 left
but if you estimate the population size, these 10 dead animals are not recaptured and the more animals you have that you never recapture the bigger is you population size.
if I take smaller intervall i get the problems with the different detectability...

that means I have 3 choices.

first: I just take the numbers I counted and be happy
second: I make a low level estimation and get stupid numbers while loosing a lot of time
third: I study biology, spend years to create the best of the best berus estimation method to finally get a better number that might be better than what I counted...or not

so i took first choise

Why do you need habitat use assumptions? You just want to estimate population size for a given spot, right?

No, titel is "vipera berus population densities"