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Evaluating population sizes and capture e |
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Vicar
Senior Member Joined: 02 Sep 2004 Location: United Kingdom Status: Offline Points: 1184 |
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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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GemmaJF
Admin Group Joined: 25 Jan 2003 Location: Essex Status: Offline Points: 4359 |
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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. 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.
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Robert V
Senior Member Joined: 06 Aug 2004 Location: United Kingdom Status: Offline Points: 1264 |
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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
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Robert V
Senior Member Joined: 06 Aug 2004 Location: United Kingdom Status: Offline Points: 1264 |
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That should be wouldn't tell, not would! Lol
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RobV
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Robert V
Senior Member Joined: 06 Aug 2004 Location: United Kingdom Status: Offline Points: 1264 |
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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
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GemmaJF
Admin Group Joined: 25 Jan 2003 Location: Essex Status: Offline Points: 4359 |
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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 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.
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Karen
New Member Joined: 15 Mar 2017 Location: Leicestershire Status: Offline Points: 4 |
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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
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rhysrkid
Senior Member Joined: 14 Nov 2003 Location: United Kingdom Status: Offline Points: 98 |
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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
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Suzi
Senior Member Joined: 06 Apr 2005 Location: United Kingdom Status: Offline Points: 1025 |
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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
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Barry
Member Joined: 14 Aug 2005 Location: United Kingdom Status: Offline Points: 6 |
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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
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