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Evaluating population sizes and capture e

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Topic: Evaluating population sizes and capture e
Posted By: Barry
Subject: Evaluating population sizes and capture e
Date Posted: 14 Aug 2005 at 1:35pm
This has been bugging me for years !
Does anyone else think it's about time we standardised all the criteria for asessing pop.size, trapping effort, key reptile sites etc etc?
You know the sort of problem : Low pop of Commom lizard (HGBI mitigatiom guidelines) = up to 20/Ha
Low pop of Commom lizard (Key Reptile sites guidelines) = up to 5/Ha.
....And why do they say a Low pop. of Adders is less than 2. surely that's 1!!!
It does my head in!


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Barry Kemp - Sussex Amphibian & Reptile Group



Replies:
Posted By: calumma
Date Posted: 14 Aug 2005 at 2:31pm
Barry,

Yes I agree that this needs some serious attention. However, the only real
way of standardising is likely to involve statistical methods that are simply
beyong most consultants.

Perhaps this would make a good workshop for the next recorders meeting??

-------------
Lee Brady

Kent Herpetofauna Recorder | Independent Ecological Consultant



mailto:recorder@calummaecologicalservices.co.uk - Email


Posted By: Vicar
Date Posted: 14 Aug 2005 at 2:47pm

I agree totally !

I've been chatting this over with Chris G-O at HCT. I have a bee in my bonnet re the assessment of likely non-presence of a species at a site too. How many visits without a sighting is sufficient? My personal view is much in line with Lee, applying statistical methods to legacy records.

The only reliable method re pop estimates I have come up with so far are any of the various mark/recapture methods. But the shortcommings of this approach are manifest. Clearly there is likely to be a two-tier approach to this; a 'quick and dirty' estimation methodology (general applications/consultants) and a more rigorous (and more accurate?) approach (herpetologists ?)

I would be very keen to actively support any widespread attempt to crack these issues.

My only slight concern with a workshop is that; a significant amount of work is necessary to crack this. So long as a workshop agrees general guidance and the will in principle to reach a common goal, and perhaps the adoption method, that's fine. Agreeing on 'numbers' without this pre-work would attain consistency, but is unlikely to be particularly useful (scientifically).

Comments ?



-------------
Steve Langham - Chairman     mailto:steve@surrey-arg.org.uk">
Surrey Amphibian & Reptile Group


Posted By: herpetologic2
Date Posted: 14 Aug 2005 at 5:23pm

 

Well there are currently mitigation guidelines being written for English Nature by Cresswell Associates - I think they may be finished - but I do know that they want to provide more information on assessing population sizes from survey results -

You left out the conservation bodies in the list of the two tier approach - there is a third lower level - where reptiles arent even bothered with - for instance in many nature conservation management plans - reptiles oh they can look after themselves......bring on the bulldozers (bovine or otherwise!)

Still wouldnt reptile surveys have to go on for several years or decades to try and answer the question - how big is the population size? wouldnt reptiles undergo the same population 'highs' and 'lows' as amphibians and other wildlife species -

The approach to the different species would be different from each other - for instance the snakes would need to be considered differently to the lizards etc

 

JC

 

PS it would make a good workshop for the next HGBI Herpetofauna Workers Meeting

 



Posted By: Iowarth
Date Posted: 14 Aug 2005 at 5:34pm

Hi all

No doubt this is something that is needed. But it is appallingly complex. I have a pretty good "feel" for Common Lizards - but there's no science - just years of experience saying "habitat looks like thus, lizards seen X thus population Y"! Not a lot of use.

With Sand Lizards for example, it is far easier to spot them and to evaluate populations in heath than in dune. With intensive surveying in heath you can get to know individuals and come up with a very good estimate. With large dune complexes you count yourself remarkably lucky to ever see the same individual lizard twice or more on separate visits.

An example is in the Merseyside dunes where we are constantly increasing the estimated population - what we don't know is whether this reflects climate change extending the population, increased monitoring, improved monitoring skills or a combination of all these factors and possibly more.

Basically, every estimate we make with these populations has been blown out of the water by further monitoring - however scientific we try to make it!



-------------
Chris Davis, Site Administrator

Co-ordinator, Sand Lizard Captive Breeding Programme (RETIRED)


Posted By: calumma
Date Posted: 15 Aug 2005 at 3:51am
The problem with any population assessment is dealing with detectability.
Ideally, the method used to estimate population size would control for
differences in detectability between different species, habitats, methods,
surveyors etc.

Also, it is important to understand what is actually being assessed.
Counting slow-worms within an old allotment may give an assessment of
population. But what does a simple count of adder in a field margin
mean?

Differences in ecology between different species, surely means that we
need different assessment methods? John Baker has gone some way
towards this in devising the 'Make the adder count' project". Although it
remains to be seen how successful counting individuals as they emerge
from hibernation will be - it is at least a start.   

-------------
Lee Brady

Kent Herpetofauna Recorder | Independent Ecological Consultant



mailto:recorder@calummaecologicalservices.co.uk - Email


Posted By: Iowarth
Date Posted: 15 Aug 2005 at 4:04am

Precisely what I was trying to indicate by example, Lee.

There are simply so many variables to take into account - we don't even know how to evaluate them. For example surveyor "skill" - what baseline do we measure from, how do we set a scale on it, how do we apply it to an individual (without causing internecine warfare ) and so on.

Inevitably some species/habitats are easier than others - the adder hibernaculum being a case in point - but even then - how confident can we be of its accuracy? Having said this almost every method we currently use can be out by several orders of magnitude - even getting +/- 50% would be a huge improvement in many cases.



-------------
Chris Davis, Site Administrator

Co-ordinator, Sand Lizard Captive Breeding Programme (RETIRED)


Posted By: Vicar
Date Posted: 15 Aug 2005 at 7:14am

I have a feeling that pop estimation methods can't progress much further without some confidence in the ground truth for a selection of sites.

Were it possible to know the population by species, for even a handfull of sites; then various methods could be tested (by species) and appropriate calibration or estimations applied to more simplified methodologies. Clearly, the more sites where this can be achieved the better, but even a small number initially would provide a good working premise.

Next comes the thorny question of HOW to we obtain such a ground truth? My thinking is that it is likely to involve detailed work over a number of years, which is why veterans' work, such as Tony Phelps(no offence intended Tony ), where sites have been monitored closely over a good number of years is so important.

I can't see a 'quick-fix' for this one.



-------------
Steve Langham - Chairman     mailto:steve@surrey-arg.org.uk">
Surrey Amphibian & Reptile Group


Posted By: Jim Finnie
Date Posted: 15 Aug 2005 at 8:09am

I'm new to this, so apologies if this is old hat:

Imagine a bag containing an unknown number of white marbles. Now add, for example, 5 black marbles which are otherwise identical to the white ones. Next spend some time withdrawing, noting the colour of the withdrawn marble, then putting it back in the bag. You can make an increasingly accurate estimate of the total population from the emerging ratio of drawn black and white marbles. If, for example, after 100 withdrawals and replacements the tally is 50 black and 50 white, we can conclude that there are probably 5 white marbles.

The key is to have a known number of recognisable individual reptiles or black marbles!. The withdrawals and replacements are of course sightings.

Hope this helps .



Posted By: Vicar
Date Posted: 15 Aug 2005 at 8:21am

Jim,

Good standard scientific approach that ! Unfortunately, it relies somewhat upon the assumption that 'detection' probability is similar, and that you WILL detect every marble, given enough time. (although I take your point about the estimate improving over time). The other issue in my mind is how many surveys are sufficient ? Adders are relatively easy to distinguish between individuals, but I have a harder time with some of the other species.

Some of our little blighters (I'm thinking of Ca), I personally find very difficult to detect visually, so tins are needed. We do see many reptile species under tins, but are these the individuals who 'like' tins ? what is the proportion of individuals who use tins ?

Nevermind the negative tone above, I actually agree whoeheartedly with the principle you suggest. Yes this is a tough nut to crack, but far from impossible to improve upon what we currently have.

Detection is key, just to fuel the debate, I offer something I've been working on, and would be grateful for comment. (this is just the headlines - lots of hidden subtleties). I'm trying to generate a simple mathematical model to assist with detection.



-------------
Steve Langham - Chairman     mailto:steve@surrey-arg.org.uk">
Surrey Amphibian & Reptile Group


Posted By: Iowarth
Date Posted: 15 Aug 2005 at 1:06pm

Hi Steve

I think you do have the beginnings of a potential mathematical model here. Unfortunately its limitation appears to be its link to species that use refugia. I suppose to an extent, with La for example, focii might give a similar input. There is still a potential weakness in that such focii are not necessarily always found - nor do we know what proportion of a given population use them. Conversely, with the refugia using species such as Ca you have effectively eliminated variability in the surveyors so at least one of the "unknowns" has been dealt with. You also raise an interesting question regarding tin usage by herps. Is it, as you say, simply certain individuals that use them. Certainly with Lv I believe that any/all individuals will use them - albeit usually basking on top rather than underneath! Nonetheless in a recent Lv/Af rescue I estimated populations based on sightings on and under tins as 250/100 in 1 Ha in four visits in good conditions multiplying individuals see by 5. Animals actually captured and removed was 450/200 - so what the hell do I know!



-------------
Chris Davis, Site Administrator

Co-ordinator, Sand Lizard Captive Breeding Programme (RETIRED)


Posted By: calumma
Date Posted: 15 Aug 2005 at 1:25pm
Steve, I would argue that your fixed factors are not actually fixed.
Tendency of species to use refugia may be dependent upon local habitat
conditions, time of day, season and weather. Population density may also
vary - especially later in the season as new recruits enter the population.

Chris, I also think that using refugia does not necessarily eliminate the
variability associated with surveyor experience. I have seen tins placed in
the most bizarre places. I guess it depends on what you are trying to
show. It would be easy to produce false negatives through inappropriate
placement of refugia...

With regard to Lv and refugia, I have found that whether animals are
found underneath or on top depends on local weather conditions and
time of day. Gemma produced a graph a while back that illustrated this
quite nicely for a site in Kent.

-------------
Lee Brady

Kent Herpetofauna Recorder | Independent Ecological Consultant



mailto:recorder@calummaecologicalservices.co.uk - Email


Posted By: Iowarth
Date Posted: 15 Aug 2005 at 2:15pm

Hi Lee

I must agree your first point, also addressed in your final paragraph. I must admit I have so little opportunity to see Lv in the wild nowadays that the generally carefully selected weather conditions late in the season would definitely produce a bias towards refugia for additional warmth. And there is no doubt about variability of population density whatever the species.

And, indeed, I stand corrected re the surveyor experience. I only get tin placement wrong intentionally (as in I've got so many I'll chuck one here in case the lizards don't agree with me) but I must admit it would be very easy to do so. In fact, in the rescue I mentioned I had a couple of inexperienced helpers at the tin placing stage. After carefully describing and demostrating appropriate locations it felt like I spent the rest of the day saying "No, not there because.....".

Makes a helluva job with Steve's model, or indeed any other when it is filled with nothing but variables.



-------------
Chris Davis, Site Administrator

Co-ordinator, Sand Lizard Captive Breeding Programme (RETIRED)


Posted By: Vicar
Date Posted: 15 Aug 2005 at 3:14pm

Cheers guys,

this is all useful debate. To be honest, I was waiting for the fixed factors comment . its supposed to represent factors beyond the control of the surveyor, the terminology is a military hangover.

As for placement of refugia, its what I mean by physical placement, although as Chris suggests, it's well worth placing tins in less obvious places. I'm a firm believer in that if you only look for targets in the places you expect to see them, then you'll only detect them where you expect. As Gemma has said before, nature doesn't follow many rules closely (or should that be absolutely?).

Part of the rationale with building any model is to expose the issues and develop understanding, its pretty much a given that any model will be wrong, its just a case of how much practical value it produces somewhere along its development.



-------------
Steve Langham - Chairman     mailto:steve@surrey-arg.org.uk">
Surrey Amphibian & Reptile Group


Posted By: Barry
Date Posted: 15 Aug 2005 at 3:22pm
I see we are getting back to refugia again! All very relevant and worthy of more discussion but we have moved away from my original point somewhat.
If HGBI could produce guidelines all that time ago (10, 15 years?) surely with the combined knowledge we have all acumulated since then we must be capable of improving the current guidelines for say, what a medium sized population of Slow worms should be or what a suitable number of refugia would be for survey per hectare of a given habitat type and what the caveats are?
One thing's for sure , at some point a compromise will have to be made between what is achievable and what is desirable.Or should we just not bother with the current guidelines?
Here's another question : Are we just wasting energy trying to find a foolproof system for accurately predicting reptile population size? After all I've always thought that a successfull translocation is when the habitat is right and you can record some breeding in the following year (s). If you moved 465 Slow worms to a perfect receptor site and surveyed it again using the most rigourous survey technique known to man you'd still not record 465 Slow worms on the receptor site the following year, well maybe if you did a destructive search !


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Barry Kemp - Sussex Amphibian & Reptile Group


Posted By: Iowarth
Date Posted: 15 Aug 2005 at 3:33pm

You have a military hangover? How unpleasant!

Further to Gemma's previous comment my parallel one which I often use is "To the best of my knowledge the lizards (or snakes, or whatever) seldom read the books by the experts." Certainly most of us have come across various herps in atypical habitat and behaving in atypical manner at some time or another.

My chief frustration in this debate thus far is that it is so easy to pick holes in someone else's ideas - but I feel terribly guilty doing so because I'm damned if I can come up with anything better! Or, indeed, anything!

The single greatest problem that I can perceive is that we do need a fixed reference from which we can work. But all the potentials appear themselves to be governed by a number of variables.

For what its worth we loosely estimate Sand Lizard populations on heath as around three times the number of individuals seen in at least four visits in otimal conditions. Even more loosely, in dune, experience so far suggests that the factor should be more like seven. But even that is difficult because the nature of the habitat is such that we might never be able to confirm our estimate.

It does, however, seem to me, that if we could assemble and analyse the results of various rescues, together with all possible details from preceding surveys of the rescue site, habitat type etc we might have something to work on. After all this is the only occasion on which we can be sure that a reasonably substantial plot of land actually surrenders all - or at least the majority - of its animals.



-------------
Chris Davis, Site Administrator

Co-ordinator, Sand Lizard Captive Breeding Programme (RETIRED)


Posted By: calumma
Date Posted: 15 Aug 2005 at 3:43pm
In fact Barry, I don't think that things have progressed very much at all.
Personally I feel that simple counts (whether collected through the use of
refugia or otherwise) mean very little with regard to reptile populations.

There are some interesting models being developed that attempt to relate
counts to population estimates but there is a long way to go before these
are likely to be used in the UK.

I'm reasonanly confident that existing techniques allow one to reliably
determine likely presence, but I agree that we really need to push for
more research projects in this area.




-------------
Lee Brady

Kent Herpetofauna Recorder | Independent Ecological Consultant



mailto:recorder@calummaecologicalservices.co.uk - Email


Posted By: calumma
Date Posted: 15 Aug 2005 at 3:51pm
Chris, it sounds like you developing a 'detectability constant'. Perhaps this is
a good starting point for where we go from here.

I agree that rescue type projects may be the best option for attempting to
determine absolute counts. However, most such projects lack the luxury of
time for collecting data in a sufficiently rigorous manner.

-------------
Lee Brady

Kent Herpetofauna Recorder | Independent Ecological Consultant



mailto:recorder@calummaecologicalservices.co.uk - Email


Posted By: herpetologic2
Date Posted: 15 Aug 2005 at 5:04pm

Dear all

I would agree that rescue sites seem to be the only real opportunity to try and answer these questions - but would the secretive reptile mitigation industry give up their records or do we need to start up a reporting scheme for consultants to report their data and findings.......ohhh another part of the NARRS project??

There are several projects looking at reptile mitigation - Cresswell Associates are looking to compare survey results with total captures - along with habitat criteria - I also know that the numbers of questionaires being returned is quite low - incidently not many reptile records or even crested newt records are passed onto local recorders - not even the BRC!!! - does make you wonder where the records are?

I feel that this debate is needed to try and push reptile conservation rather than 'protection' - translocating thousands of reptiles is clearly not conservation - rather the focus should be on habitat protection, creation, enhancements and monitoring - Research should also be included in reptile mitigation schemes - an agreed format of recording data across the country would help - Reptile habitat suitability index, standard survey methods etc

JC

 



Posted By: Iowarth
Date Posted: 15 Aug 2005 at 5:33pm

Barry, obviously you fired up an interesting debate but you are right, we have strayed from your initial question. Returning to your specific point while what you say sounds good in theory I am unsure it holds good in fact. I am, for example, unsure of the origin of the HGBI figures you quote. If you hunt around enough you will find density figures here and there BUT most of them are either informed guesses, specific to only one habitat type/climate etc or simply quotes of the other two.

Now, having said this, from nothing but personal experience (informed guess!) I would not disagree greatly with any of the figures you quote. Less than 20 Common Lizards per hectare is certainly a very low density population - and, by definition this includes 5 (which is a very, very low density!). So far as Adders are concerned these are found at much lower densities and over wider areas. Thus, 15 adders over 10 hectares represents 1.5 per hectare - certainly both a low density and less than 2 !

Conversely most of those 15 adders might be stuffed into 1 hectare and most of the 20 lizards stuffed into 20 x 20 metres within the hectare. This is one respect in which even measuring density as animals per hectare can be grossly misleading. Clearly, if 15 of the Common lizards were in prime habitat of 400 sq metres we would have a population density there of 375 per hectare which represents a reasonably dense population (and yes, I know a population fairly near me that does broadly match those figures).

I am, in fact, less than convinced that we can improve significantly on these specific definitions. The real problem is that which this thread has people trying to address - not what constitutes as low/medium/high density - but how, other than by destructive search can we calculate density.

So, I think that we are actually moving towards what you want - or at least trying to. If we had a reliable method of assessing populations (and note I say populations rather than population density) then we would be in a position to re-define low/medium/high density - if necessary.

Lee, you are quite correct in that I am seeking a "detectability constant". Still a variable constant but one that varies within definable parameters so could become an absolute in each specific locale. I recognise that it might not be truly scientific and disciplined - but nonetheless better than what we have.

Sadly, as Jon says, there do seem to be a number of members of the mitigation/consultancy business who do not seem to be prepared to share this information. Generally, and unsurprisingly, these seem to be the ones who regard it as money for old rope and have little care or concern for the animals themselves. So, while I think my proposal has some validity, as Cresswells are discovering it may still not be wholly practical.



-------------
Chris Davis, Site Administrator

Co-ordinator, Sand Lizard Captive Breeding Programme (RETIRED)


Posted By: Vicar
Date Posted: 15 Aug 2005 at 7:17pm

Just to throw a spanner into the works, and for my own personal education.

Why are absolute population figues useful ?

I'd suggest..(OK playing Devil's advocate quite heavily here ), that for monitoring purposes, if the goal is to determine how well an individual population is responding, to say a management practice, why not have a sucession of similar surveys (monitoring). If sightings go up (adjusted for suitable conditions etc), then the trend is healthy, conversely, sommit's wrong.

The current froglife numbers representing relative population densities could still be fit for purpose in determining key reptile sites, even though they may be arbitary figues.

I say this, as I have mapped the current (old) La SAP to a proposed action plan, and actually a relatively small percentage of goals actually require population numbers, and even when required, I suspect that trend analysis would do just as well.

Tho it is getting late and I'm noticing senility creeping in recently, just thought I ought to ask the 'stupid/obvious question'.



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Steve Langham - Chairman     mailto:steve@surrey-arg.org.uk">
Surrey Amphibian & Reptile Group


Posted By: calumma
Date Posted: 16 Aug 2005 at 3:34am
Steve, in principal what you propose is quite valid and would represent a
relative abundance that can be monitoring over time using the same
methodology.

However, the problem comes back down to detectability. If the
management work simply alters a species detectability, any changes in
relative abundance may not actually represent changes in actual
population.

Calculating absolute population figures are important, since they help us
to determine the detectability baseline upon which estimates of
population can subsequently be derived.

With appropriate models, it is possible to estimate density in a way that
controls for detectability. However, existing methods (e.g. capture/
recapture) require considerable effort.

Chris has highlighted another important issue by reminding us that
reptiles tend not to be evenly distributed across any given site. Animals
tend to be patchy in their distribution. A surveyor who randomly samples
a very patchy population may underestimate density (although this will be
overcome with increasing effort), while an experienced surveyor who only
targets focii could overestimate density for the site as a whole.

Edit: I should add, that as surveyors we tend to fall in the latter category -
concentrating our effort in those areas where we expect to find animals.
Not unreasonable from a presence/likely absence survey perspective, but
hopelessly biased when using the simple counts that are derived for
estimating relative populations.

-------------
Lee Brady

Kent Herpetofauna Recorder | Independent Ecological Consultant



mailto:recorder@calummaecologicalservices.co.uk - Email


Posted By: rhysrkid
Date Posted: 16 Aug 2005 at 2:01pm

This is great stuff.

IĈm keen to know how these ideas work with sites where animals immigrate and emigrate.  With the sites that I work on that support N natrix I have been undertaking a capture-mark-recapture study (using photos of belly markings).  I tend to find that some individuals stay (good reliable folk!) whilst others appear for a few weeks before never being seen again.  Of course this can be down to mortality but given the species habit of having large home ranges it is just as likely that they have simply moved away from the study area.  Similarly, many new individuals are seen with each survey.  This could be due to high recruitment rates or alternatively immigration of individuals from other areas.  When determining the population size how big does the survey area have to be in order to ascertain an accurate popn size?  Would you have to survey an area that covers the maximum distance individuals would travel? If the number of individuals recorded is high is this a true reflection of the actual number relying on the site as key habitat or simply a reflection of many individuals passing through? We work within geographical boundaries such as site borders, development area or counties for example.  As others have mentioned, herps care little for our way of thinking and tend to go where ever they want. Forgive me if this is not relevant, if it has already been mentioned or is straying from the main thrust of maths and models!



-------------
Rhys


Posted By: calumma
Date Posted: 16 Aug 2005 at 2:08pm
Rhys, the most robust population estimate models should control for
emmigration and immigration. Most of the more basic techniques
unfortunately assume a closed population. The problem with expanding
survey areas to cover an individuals range is that you will encounter new
individuals and have to increase your area to include all of their range, with
the reult that you will encounter new indivi.......   

-------------
Lee Brady

Kent Herpetofauna Recorder | Independent Ecological Consultant



mailto:recorder@calummaecologicalservices.co.uk - Email


Posted By: Vicar
Date Posted: 16 Aug 2005 at 5:15pm

heh ! having started to develop a model (and reviewing similar models), yes some do cater for migrant specimens. Mine certainly won't for the first few passes !...its difficult enough as it is !

What I am already finding is...even rough data, based upon extemely simple assumptions just isn't there, but then one of the 'benefits' of creating models is that it always leads to applied research requirements.

Out of interest; I'm dabbling with the concept of distribution probabilites of a given population, chance of encountering, say, refugia, and detection probability. I very much doubt this will result in a method for estimating a population from survey results, but it will force me to consider,and quantify (where possible) the variables together with their relationship. This could be a complimentary approach to that being followed by Cresswell.



-------------
Steve Langham - Chairman     mailto:steve@surrey-arg.org.uk">
Surrey Amphibian & Reptile Group


Posted By: administrator
Date Posted: 16 Aug 2005 at 5:18pm

One can't help thinking of Einstein on his death bed attempting to mathematically model the behaviour of sub-atomic particles.. Albert.. it is chaos!!

I was pondering the same problem as Rhys. Consider a site that lies in the base of a valley. I survey the 40 acre area in the early spring and record a small number of adder regularly under refugia. I determine a likely hibernation area. I consult my database of records and run the numbers through my mathematical model and conclude that I am dealing with a low-density population.

I plan mitigation, I erect exclusion fencing in June. During August I start to remove 8 adders a day from the site and after 2 weeks there is no sign that the numbers are reducing. My receptor site is totally inadequate I am now panicking and wondering why on earth my survey data did not reveal the numbers on site.

Of course I overlooked that the site at the base of a valley was a foraging area serving 6 separate locii located on the escarpment 1km away and large number of animals moved onto the site before the exclusion fence was erected but after I completed my presence absence surveys

Probably a very extreme example, but I wonder how a mathematical model could cope with this sort of fluctuation? Clearly if the surveys had extended throughout an entire season it is likely that the true nature and importance of the site to adder would have been established.. but how many consulultancy based surveys extend for the entire season? One salient point arose during my time working with mathematical models for fluid flow, rubbish in, rubbish out!

Which leads to the bottom line, we need to look at standardising survey techniques, in my opinion presence absence is inadequate to base a mitigation on and not conclusive in many circumstances.



Posted By: Iowarth
Date Posted: 16 Aug 2005 at 5:30pm
Your final line sums it up Gemma - to quote Chris G-O " The absence of evidence is not the same as the evdience of absence"

-------------
Chris Davis, Site Administrator

Co-ordinator, Sand Lizard Captive Breeding Programme (RETIRED)


Posted By: calumma
Date Posted: 17 Aug 2005 at 3:55am
Gemma, for your example substitute gcn for adder and breeding pond for
focii - would that be considered acceptable?

I really think that we need different techniques that adequately address
the very real differences between different species. This is especially
important when considering species such as adder, that may display
significant temporal differences in habitat occupancy and subsequently
local distribution. In the example you quote, I would argue that different
population estimates should be generated (where possible), one for each
component of the metapopulation.

It's interesting that for amphibians, we generally only estimate
populations from breeding adults in ponds. Yet for reptiles, we assume
that simple counts are a true reflection of population - even when some
of the same metapopulation dynamics may be at work...

Alas, I also don't think that much of this debate is relevant for
consultancy - at least not at the moment. The level of legal protection
that widespread species receive (and consequent lack of mitigation
licensing - even for adder), means that consultants can meet their client's
legal requirements without worrying too much about any of this stuff.

If we as practicing herpetologists (conservationists and consultants) can
help to coordinate a large-scale project that attempts to address some of
these issues, then perhaps we can help to influence change?

-------------
Lee Brady

Kent Herpetofauna Recorder | Independent Ecological Consultant



mailto:recorder@calummaecologicalservices.co.uk - Email


Posted By: Vicar
Date Posted: 17 Aug 2005 at 9:01am
I suspect, in this context, it refers to gaining appropriate evidence of the likely non-presence of a species. Not seeing a species on one trip is probably insufficient evidence to suggest its likely absence. This then leads to the question of how many site visits in suitable conditions are necessary before we make the judgement that a particular species is probably not present.

This should be a fairly easy one to crack using analysis of historical evidence. Number of visits are likely to be different by species, especially concering Ca ? But existing records should provide a distribution of number of site visits until a particular species shows up, so putting a figure on this with a degree of confidence (in general terms) should be cake compared to some of the issues on this thread :P


-------------
Steve Langham - Chairman     mailto:steve@surrey-arg.org.uk">
Surrey Amphibian & Reptile Group


Posted By: administrator
Date Posted: 17 Aug 2005 at 10:51am

Population dynamics and spatial distribution of the adder Vipera berus in southern Dorset, England

Tony Phelps

http://herpetofauna.co.uk/forum/uploads/GemmaJF/2005-08-17_104609_phelps72dpi.pdf - Click



Posted By: Iowarth
Date Posted: 17 Aug 2005 at 12:20pm

Gemma, thanks for posting that link.

Tony, your paper is excellent and gives a tremendous and hitherto lacking insight into adders and their behaviour. I think you also illustrate by contrast one of the great weaknesses of most research. Very seldom does it involve genuine detailed long term study of any of our native herps in their wild state - all too often, the opposite - short term studies in artificial conditions based on unwarranted assumptions leading to foregone conclusions.

I for one deeply admire the dedication you have put into your studies and regard your work not only as invaluable but as an example of what should be done if we are going to gain a thorough understanding of our herps.

Thanks again

(That's all, grovelling congratulations aren't my style even when so thoroughly deserved!)



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Chris Davis, Site Administrator

Co-ordinator, Sand Lizard Captive Breeding Programme (RETIRED)


Posted By: Iowarth
Date Posted: 17 Aug 2005 at 1:00pm

Cheers Tony - was that tears of hysterical laughter?

Seriously it is damned good. And a shining example. Can't wait to see the rest (but you're not going to charge $40 per seven pages are you?)

And I wouldn't worry - a lot of people die young for lack of interest. You're not going to have that problem - keep going - being in your age group I just hope I that I am around to see the results!



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Chris Davis, Site Administrator

Co-ordinator, Sand Lizard Captive Breeding Programme (RETIRED)


Posted By: Barry
Date Posted: 17 Aug 2005 at 2:51pm
When I started this topic I never thought we'd end up quoting Carl Sagan and talking about UFO's !

So, can we wrap0 it up - who wants to see some updated,reasonably sensible criteria for population assessment - limit your answers to no less than 6 words !!

And Tony, I hope you do live to 104, or at least until next Tuesday when we're due to meet !!

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Barry Kemp - Sussex Amphibian & Reptile Group


Posted By: Suzi
Date Posted: 20 Aug 2005 at 8:15pm

Would it be possible that chosen methods for evaluating pop. size if standardised across the country might prove misleading?

I'm thinking of refugia, ground temp, air temp etc. and wondering if any of you who have worked in both the warmer and cooler counties might have noticed distinct differences in reptile visibility that could lead to misleading evaluations.



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Suz


Posted By: rhysrkid
Date Posted: 23 Aug 2005 at 2:38pm
When I was in Malaysia a herpetologist I was working with said to me: "I wish someone would invent a set of goggles that makes vegetation transparent, leaving all the herps suspended in mid-air.  It would make surveying a hell of a lot easier...".  Sometimes I'm inclined to agree with him!  It would certainly make popn estimates a little less of a headache!

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Rhys


Posted By: Karen
Date Posted: 21 Mar 2017 at 1:41pm
Hi Everyone

I am currently doing a dissertation on this very subject (with regard to Common Lizards) for an MSc and wondered if there were any scientific papers out there that anyone could refer me to. I've had a look and there doesn't seem to be anything specific re Common Lizard population estimates. Was any work done since this forum thread was started? Any help would be much appreciated. 
Karen


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Karen


Posted By: GemmaJF
Date Posted: 22 Mar 2017 at 7:26pm
I do not know anything specific for common lizards. I think perhaps look for papers regarding population estimates for reptiles and amphibians in general. 

If you take a look at the Narrs protocols it does mention software such as MARK and gives a couple of references to scientific papers on pages 4/5
http://www.narrs.org.uk/documents/Survey_protocols_for_the_British_herpetofauna.pdf" rel="nofollow -
http://www.narrs.org.uk/documents/Survey_protocols_for_the_British_herpetofauna.pdf" rel="nofollow - http://www.narrs.org.uk/documents/Survey_protocols_for_the_British_herpetofauna.pdf

Not sure about your idea for photography. They are not like newts that can easily be put in a squish box, though there may be others who have had success with doing so. 


Posted By: Robert V
Date Posted: 04 Apr 2017 at 2:10pm
Gemma / Karen,
 
the guidance in the NARRS protocols still suggests repeat capture and re-capture "techniques", but today the generally accepted opinion is that capture (let alone repeated capture) of Grass Snakes, Adders etc, impacts negatively on their lives.
 
It's all very well looking to study such an endearing little creature as the common lizard, but maybe from a distance. I fully appreciate that this "research" may not give the fancy pie charts and axis data graphs that are so loved by educational establishments when marking papers (they appear to give little value to field craft and welfare of the animals involved) but there you are.
 
I can walk through one of my favourite spots and see loads of them charging about.
 
I would tell the "record pool" or anyone else as some people on this forum seem to think (not you gemma don't worry) its ok to go and collect up polymorphs, take them from site, DNA sample them etc etc, and completely upset the daily bio rhythms 9if that's how you spell it!) of the sites.
 
Karen, I can show you a terrific site in Essex, but I'd need a reassurance of complete security of site information, location, everything. Even in your MSc.
 
R


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RobV


Posted By: Robert V
Date Posted: 04 Apr 2017 at 2:11pm
That should be wouldn't tell, not would! Lol


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RobV


Posted By: Robert V
Date Posted: 04 Apr 2017 at 2:16pm
And you come across individuals like this that has just lost some of his tail but otherwise looks to be in good health...

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RobV


Posted By: GemmaJF
Date Posted: 08 Apr 2017 at 8:01pm
I do agree Rob, I just wanted to point Karen to possible academic papers, that does not mean I am advocate of the methodologies contained within them. Wink The only reason I can see for capturing any of these animals 'en-masse' is to move them during a mitigation. I doubt really even then it is truly justified or does much good in the end.


Posted By: Vicar
Date Posted: 09 May 2017 at 1:16am
Over the last 12 years since I last posted on this thread...(is that possible? where did the time go?)

In Surrey, we have over 100 reptile sites that we've been systematically surveying for almost 10 years (>50K data points). Detection rates for each species vary dramatically by site. I've been trying to correlate the frequency of sightings to conservation status (population dynamics), but I can't do it from sightings alone.

Where habitat has been degraded, you see more animals (less cover to hide in...until they're predated), so that's a negative correlation. There are also year on year fluctuations. Almost the only useable sighting metric is peak count, as there must be at least that many of any species present. It's just not a very useful metric.

You can get population estimates from mark-recapture, which we do for all smooth snakes and increasingly for adder (using at-distance photography for Vb). The practicable solution is going to be a combination, using population modelling based on mark-recapture factors (weightings), probably on a site by site basis. We're not there yet, but we are closer than we've ever been.

A better route may be to look at the area occupied by a species, as this seems to be a far more stable measurement. We're probably too hung up on numbers, although habitat 'quality' for the occupied area is clearly important.

My 2p.


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Steve Langham - Chairman     mailto:steve@surrey-arg.org.uk">
Surrey Amphibian & Reptile Group



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