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GCN terrestrial habitat range

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Matt Harris View Drop Down
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Matt Harris Quote  Post ReplyReply Direct Link To This Post Topic: GCN terrestrial habitat range
    Posted: 05 Nov 2012 at 1:46pm
We often read things like "the majority of animals probably stay within about 250m of the breeding pond" or "the vast majority of animals are found within a few hundred metres of the breeding pond" and that juveniles can variously disperse 900m, 1Km, 1.3 Km etc from natal pond, but I wondered if there were evidence-based percentage figures attached to the 250, 500, 1Km radii that are often advised, e.g. do 95% of terrestrial animals occur within 250m of a breeding pond, 99% within 500m etc?

Clearly at the level of the individual pond, there will be a range of factors such as suitability of habitat, presence of barriers/dispersal corrifdors etc, but does anyone know of research that has looked at the average dispersal distance from breeding ponds?

Or did someone just pluck 250 metres out of the air?

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GemmaJF View Drop Down
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Post Options Post Options   Thanks (0) Thanks(0)   Quote GemmaJF Quote  Post ReplyReply Direct Link To This Post Posted: 05 Nov 2012 at 5:10pm
Probably someone just picked 250 metres out of the air Matt. Logically as they only have little legs one might expect much higher concentrations around the breeding pond and this reducing with distance from the pond(s) used for breeding. So it is rule of thumb stuff.

No doubt though there are lots of modifiers and it isn't a rule. It would depend on the proximity of suitable foraging habitats, etc etc. I have little doubt from my own observations of native amphibians that many juveniles disperse widely from breeding ponds. After all most species take two to three years to become sexually mature and not all will return to ponds during that time. I have often observed for example concentration at the edge of motorways, along borders with arable fields which suggest they move some distance which stops when reaching a barrier. So one could find a high concentration of animals an appreciable distance from an obvious breeding pond if such circumstances existed within say a development site.

I'm sure we have also all encountered odd individual GCN at times turning up in ponds which do not normally support them and this again suggests distance dispersal.

Of course the problem is if someone says 250m or 500m in guidelines it becomes dogma. I certainly know of cases where ponds falling just outside this range have not been surveyed and also cases where consultants have requested data to that sort of limit of a site boundary, rather than a more pragmatic request such as within 2Km of the site.

Clearly though concentration of animals will be expected to reduce. If you draw a circle 250m around a pond it has a much smaller area than a 500m one and a substantially smaller area than one 2Km so detectabiilty will become an issue. Though there is nothing at all to say that one couldn't find a high concentration of animals within that larger area at all.


Edited by GemmaJF - 05 Nov 2012 at 5:21pm
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Mark_b View Drop Down
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Mark_b Quote  Post ReplyReply Direct Link To This Post Posted: 05 Nov 2012 at 6:36pm
Hi Matt,
 
I have emailed you an extract from The Crested Newt – A Dwindling Pond Dweller
by Robert Jehle, Burkhard Thiesmeier and Jim Foster (2011).
 
If you wish to buy the book, look here for details....
 
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Matt Harris View Drop Down
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Matt Harris Quote  Post ReplyReply Direct Link To This Post Posted: 06 Nov 2012 at 10:02am
Ok thanks for your responses; I asked the question more in hope than expectation really as I suspect the answer lies among the many things we don't know about species such as this. I did wonder if the 250m and 500m distances that are so often regurgitated were based upon any particular studies, but from the few examples quoted in the extract from Jehle, which Mark has kindly sent to me, it does seem that an average of 250m is too small a radius to encompass a reasonable majority of the population.
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Noodles View Drop Down
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Noodles Quote  Post ReplyReply Direct Link To This Post Posted: 06 Nov 2012 at 11:28am
I was about to recommend the same book, it has good chapters on home range/dispersal and a thorough reference section listing all the latest scientific papers if you want to go further. 

One of the studies (mentioned in the book) found that the vast majority of the population sheltered within 50 m of the pool, although this is certain to depend on the availability of suitable habitat etc etc. If you talk to most people involved in GCN mitigation, this capture distance is common in many of the more 'typical' cases.

In a UK study, Baker and Halliday found that new ponds were not colonized within 400 m of existing breeding pools, although this is never going to be a set rule. You can get the paper from the BHS if you are a member. 

Some of the NE research reports, based on capture returns from mitigation cases, are very useful and free to upload from the NE website; in particular try the Cresswell report ENRR 576 and the DICE stuff. Just a few ideas; although there are countless more. 

The standard 250 m is accepted as the extent of a 'typical' home range (maybe larger in a non-isolated meta-population) and there are plenty of studies to support similar distances used (greater or lesser). Doesn't mean you are always going to find many adult animals beyond 100 m or so of a pond though! Also, typical home range or meta-population dispersal should be viewed differently from the distance an individual animal COULD or sometimes might travel......500 m, 1 km, 1.3 km, 2 km etc etc! If i remember rightly, Jehle et al suggest the maximum extent of nightly migration to be 100 m (based on several studies), which indicates the potential distance an animal could disperse during an active season, if desired. The fact that most animals appear not to do so is more telling.

Also home ranges/dispersal distances are always going to vary depending on habitat quality/availability and distribution, yearly or seasonal environmental changes, habitat losses/gains, animal age/sex/health, seasonal changes in resources, hibernation migrations etc etc. It should be possible to analyse at least some of these things when looking at a site and form a reasonable hypothesis as to what is going on (in the absence of a detailed survey).

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Caleb View Drop Down
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Caleb Quote  Post ReplyReply Direct Link To This Post Posted: 06 Nov 2012 at 2:24pm
Originally posted by Noodles Noodles wrote:

One of the studies (mentioned in the book) found that the vast majority of the population sheltered within 50 m of the pool, although this is certain to depend on the availability of suitable habitat etc etc. 

If it's the same one I'm thinking of, then you can get the full paper here: http://www.rana-internet.de/media/Sonderheft4_Muellner.pdf

The implication of the paper seems to be that adults will leave for known good habitat, and stop as soon as they find it (so the distance they travel will depend on how close that habitat is), but that juveniles will keep on wandering.
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GemmaJF View Drop Down
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Post Options Post Options   Thanks (0) Thanks(0)   Quote GemmaJF Quote  Post ReplyReply Direct Link To This Post Posted: 06 Nov 2012 at 3:14pm
I was looking for that paper the other night Caleb so thanks for the link. I think one could see why in practical terms mitigation would concentrate on the adult population and for sure I would believe that the bulk of the breeding population would most likely be within 250 m of the pond. I think one of the other points made in the summary was the importance of terrestrial habitat. I doubt a factor anyone on here would overlook but it is amazing how often one comes across consultants who simply don't get that it is at least if not more important than the pond. If a pond dried up one year it would not wipe out a population, if the terrestrial habitat is destroyed, it probably would!
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Richard2 Quote  Post ReplyReply Direct Link To This Post Posted: 06 Nov 2012 at 3:48pm

This Spring I happened upon some survey work taking place on the Isle of Purbeck. Chatting to the surveyor, who runs a business providing this and other ecological services, I was surprised to hear that GCNs were apparently moving between this pond and another about half a mile away across rough pasture, during the one breeding season. Individuals had been trapped in both ponds in the same season. I didn't know they did this. Sorry the information is so inexact.

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Post Options Post Options   Thanks (0) Thanks(0)   Quote herpetologic2 Quote  Post ReplyReply Direct Link To This Post Posted: 07 Nov 2012 at 11:15am
Originally posted by Matt Harris Matt Harris wrote:

Ok thanks for your responses; I asked the question more in hope than expectation really as I suspect the answer lies among the many things we don't know about species such as this. I did wonder if the 250m and 500m distances that are so often regurgitated were based upon any particular studies, but from the few examples quoted in the extract from Jehle, which Mark has kindly sent to me, it does seem that an average of 250m is too small a radius to encompass a reasonable majority of the population.

Basically the figure of 500m was the halfway point that the maximum distance of a newt has been tracked to in various studies - one in particular a female newt was logged over 1km away from her breeding pond. The SNCO and advice 10 or so years ago came down on up to 500m from breeding ponds.

The 250m figure comes from consultancies who are looking at ponds across a large area of land - the argument being that the ponds within 250m of a developement were more important for survey than the ones 500m or 1km away as a way of cutting down on the number of surveys required to assess a road or similar development. As there is often a requirement of 6 survey visits on each pond with gcn presence you can see where this would never end if you happen to have ponds within 100 metres of each other but no significant barriers like roads and large rivers etc

There is research on this by Cresswell et al in the UK - 'An assessment of the efficiency of capture
techniques and the value of different habitats for the great crested newt Triturus cristatus
English Nature Research Reports 576'

In the summary this can be seen
'By far the most captures were recorded within 50m of ponds and few animals were captured at distances greater than 100m.'

It would be down to the assessment of the habitats on the ground. The further away from a recruiting breeding pond you go the less newts will be found - is that fair to say?



 


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GemmaJF View Drop Down
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Post Options Post Options   Thanks (0) Thanks(0)   Quote GemmaJF Quote  Post ReplyReply Direct Link To This Post Posted: 07 Nov 2012 at 3:10pm
It's fair to say if one assumes totally uniform habitat Jon. 

As I mentioned above it is possible to find high concentrations of newts away from breeding ponds. These most likely represent animals that 'wandered' as juveniles and eventually reached a barrier. In all cases the location of suitable terrestrial foraging habitats will act as a modifier.

I think capture rate would decrease away from the pond. Clearly even if the majority of animals traveled further than 50m it would be far more difficult to detect them in the area of a 100m circle than one of 50m.

That's what worries me, people don't seem to see things like that. 'We caught the majority of the population within 50m' - could be 'we found newts far more detectable at 50m' couldn't it? In fact the largest portion of the population could have been at 50m + or 250m + but much more spread out and therefore far more difficult to detect.

There is a lot of assumption here that the 'population' represents the breeding animals, it's much like the discussion on the other thread, an inward looking site by site analysis which on many occasions misses the wider picture.


Edited by GemmaJF - 07 Nov 2012 at 3:16pm
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