RAUK - Archived Forum - Response to habitat fragmentation

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Response to habitat fragmentation:

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Vanderklam
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Posted: 20 Sep 2009

Hi guys,

Im currently looking to test the role of habitat fragmentation in influencing sub-population size and structure of the adder on some of my sites this soming spring. However, when predicting a species response, I have found that I have come to a bit of a cross roads.

According to population genetic theory, small, fragmented populations are at high risk of extinction due to genetic drift and inbreeding potential. I would expect the carrying capacity of patch habitats to become reduced with increased fragmentation, and therefore inndividuals to disperse and colonise sub-optimal habitats. However, is this a justified prediction given that the species is well known for its high degrees of site fidelity?

HELP!!


Kevin Palmer
Lecturer in Animal Management/Course Manager
Reaseheath College
Vicar
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Posted: 20 Sep 2009
Hi Kevin,

Interesting....
Is the assumption for reduced carrying capacity based on the reduction in available habitat, or some function of reduced fitness?

Some observations spring to mind:
Practically, most fragmentation occurs due to development, which provides habitat barriers, so the option of sub-prime habitat is not available.

I suspect that the key issue with site fidelity is the hibernaculum. Sometimes the same hibernaculum is used by many generations, as it has proved effective as protection from predators and the elements (including flood).

Fragmentation would certainly affect migration , and when denied a suitable migration route, the adders will become more static in nature...enforced by habitat barriers.

Another observation is that even where there are acres of what appears to be prime habitat, adders still show up in foci. There is something about an area which is more attractive to the adder, that I can't fathom. Most foci in Surrey are associated with tree lines (even on heathland). I have little doubt that should these foci be made inaccessible, then the adder could survive in what appears to be nearby prime habitat...but we're back to the question of hibernaculum importance.

There should be some good examples from the consultants on the forum with on-site mitigation...assuming follow up surveillance is conducted.

Steve Langham - Chairman    
Surrey Amphibian & Reptile Group (SARG).
Vanderklam
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Posted: 20 Sep 2009

Thanks for your input Steve. My study sites feature predominantly on a local AONB, where by the majority of the established sub-populations are within SSSI's. so I am lucky in that there is immediate protection from development. So from what I have observed over the past years, is that it is habitat disturbance,manifested from recreational activity and inappropriate habitat management, that are considered the foremost threats here. I am currently working with the local landowners and managing authorities to provide increased security to some of the more vulnerable habitats (e.g. hibernacula and lying out areas. Certainly there is an issue of potential isolation of sub-populations here, but Im still conducting baseline surveys here to map the distribution of spring assemblages for the area.

What is interesting in particular is a small sub-population that became isolated on a single linear remanant fragment following heath burns being implemented on the site in 2004. I have not observed any female activity on this site for over three years, and so I may have a "bachelor" group of males on my hands here. I suspect that many individuals have dispersed and recolonised new areas as the heath has gradually regenerated over the past five years.

Best


Kevin Palmer
Lecturer in Animal Management/Course Manager
Reaseheath College
Vanderklam
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Posted: 20 Sep 2009

Oops!! Forgot to mention Steve that Im thinking mainly  along the lines of reduced carrying capcity as a function of habitat quality and quantity!


Kevin Palmer
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Reaseheath College
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Posted: 20 Sep 2009
Thanks Kevin,

That makes more sense.

I don't know.

Thinking from an evolutionary perspective it seems likely that they would evacuate a poor area.

Also, from personal experience, I have seen Adder populations 'crash' after poor habitat management, or increased pressure, and this change has on occasion been so dramatic that I can't believe it was a long-term effect.

But, does than mean the adders population suffered high and dramatic mortality (unlikely), that they went to ground more and became more difficult to observe, or migrated across suitable habitat to a new prime location? - anybody's guess. It would need mark-recapture analysis.

If you make the assumption that emigration from a poor area occurs, I guess your next steps are to try to establish thresholds for habitat size and quality which would initiate such emigration.

I have no idea where you could get data to support these assumptions, and an experimental approach isn't occurring to me at the moment (that would be palatable).

I'm happy to be a sounding board, if that helps.

Steve Langham - Chairman    
Surrey Amphibian & Reptile Group (SARG).
Vanderklam
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Posted: 20 Sep 2009
Thanks Steve. Indeed there are many problems associated with formulating a palatable experimental design. Firstly there is no universal approach to measuring habitat fragmentation. Do I use the amount of edge, the area of interior habitat, distance between suitable fragments etc etc. There are so many boundaries that would require definition. I was thinking along the lines of a comparative study between sub-populations, that is comparing sub-population size and structure using a mark and re-capture database i have against patch size. Im working under the assumption that it sub-population size should be relative to patch size, but there are obviously additional variables to factor in. More thought needed I think.........
Kevin Palmer
Lecturer in Animal Management/Course Manager
Reaseheath College
Vicar
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Posted: 20 Sep 2009
Just something that springs to mind....

If habitat and sightings were represented in a grid, you could determine habitat suitability by correlation against known locations, then apply this to the habitat set to get a data set of suitable habitat (possibly graded).

You might then choose to use cluster analysis (DBSCAN etc) to determine whether there is significant correlation between clusters of sightings & habitat. Using habitat clustering should show up fragmentation (provided a suitable grid size is chosen).

Of course this still doesn't allow you to determine the actual population present. Not even mark-recapture will give you that, although it may provide a lower confidence limit. But if a model framework exists, assumptions can always be improved later through applied research.

Steve Langham - Chairman    
Surrey Amphibian & Reptile Group (SARG).
Vanderklam
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Posted: 20 Sep 2009

Hmmm not a bad idea!! I already have all sightings over the past two years mapped on satellite images using GIS, so it would actually be realatively simple to investigate correlations between sightings and habitat. I could also use the same GPS and satellite images to map heath fragments that are utilised by sub-populations to estimate edge area and interior habitat area. Certainly there is a scope to do this kind of thing. I will keep you updated on developments as it would be useful to have your input Steve.

Best


Kevin Palmer
Lecturer in Animal Management/Course Manager
Reaseheath College
GemmaJF
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Posted: 21 Sep 2009

Anecdotal observation, I think adder attempt to carry on 'business as usual' in these situations. I have first hand observations of them attempting to cross entirely barren soil scrapes using what limited habitat remained as cover. My gut feeling is that this leads to higher mortality rates and the population crashes. I don't see any evidence of them 'moving' to suitable habitat elsewhere, simply some individuals become more and more sedentary in what existing habitat remains, the others being lost to predation as they attempt to carry on as normal. I have also observed this with spring dispersal and the males setting up surface dens, they continued to utilise the habitat they had tradionally used that remained, even in cases where it was a tiny fragment of what existed before management. Other 'apparently' suitable habitat nearby being ignored.

Be interesting if your studies support my pessimistic view Kevin.

GemmaJF40077.6634722222
Gemma Fairchild, Independent Ecological Consultant
Vanderklam
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Posted: 21 Sep 2009

Aye, my own observations would support what you have seen GF. I have previously tracked a male for over an hour on one occassion, including across totally barren landscapes. Observations by TP confirm the idea that habitat distrubance, particularly within hibernacula and surface den sites may lead to increased mortality rates within males due to their basking habits. This also suggests that adders indeed just carry on with their regular behavioural patterns. So it is a possibility for adders to respond in the same way with regards to dispersal.

Thanks for your input GF


Kevin Palmer
Lecturer in Animal Management/Course Manager
Reaseheath College
Vicar
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Posted: 21 Sep 2009
I suspect that scent trails my be important for Adder, with a certain degree of 'auto pilot' when following a trail.

I'm pretty sure that basking sites are sometimes chosen due to scent markers, as they seem able to pick a basking spot before vegetation growth, which remains in sunlight.

Time of year will also be a factor to consider, as males in mate-search mode seem oblivious to pretty much anything, including available cover.

Steve Langham - Chairman    
Surrey Amphibian & Reptile Group (SARG).
Jonathan
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Posted: 21 Sep 2009

[QUOTE=Vicar]Time of year will also be a factor to consider, as males in mate-search mode seem oblivious to pretty much anything, including available cover.
[/QUOTE]

 

Quite true, I watched a male in May 1985 search all around a busy car park next to the heathland, on one occasion I had to step in to stop a car parking on him, my footfall or movement attracted him toward me at great speed.

This location was also at least 200m away from the nearest colony, quite bizaare.

Jonathan40077.8360648148
"England Expects"
herpetologic2
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Posted: 22 Sep 2009
[QUOTE=Vicar] I suspect that scent trails my be
important for Adder, with a certain degree of 'auto
pilot' when following a trail. I'm pretty sure that
basking sites are sometimes chosen due to scent markers,
as they seem able to pick a basking spot before
vegetation growth, which remains in sunlight.Time of year
will also be a factor to consider, as males in mate-
search mode seem oblivious to pretty much anything,
including available cover.
[/QUOTE]

Its the markings on the male adder which seems to provide
protection from bird predators.

I have often thought that a freshly sloughed male adder
making its way across a short sward would be a sitting
duck - but evidence collected from those plasticine
models in Portugal, England, Wales and Sweden suggest
otherwise

Jon
Vice Chair of ARG UK - self employed consultant -
visit ARG UK & Alresford Wildlife
Vanderklam
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Joined: 20 Apr 2008
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Posted: 22 Sep 2009

Interesting stuff chaps!! Jon do you know of a link to this evidence, or is it yet to be published? But anybody have any ideas of how best to measure degrees habitat fragmentation. I could (I guess) combine many variables i.e. amount of edge, area of interior habitat, distance between frags  (using GIS) etc. Any other suggestions??

Grateful for the input as always

Kev 


Kevin Palmer
Lecturer in Animal Management/Course Manager
Reaseheath College
armata
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Posted: 27 Sep 2009
Steve - glad you mentioned 'tree lines' in association with hibernacula, this does seem to be the case in the majority of situations. In effect causes a microclimate somewhat different to the surrounding general habitat. In more open areas, deep gulleys with mature heather would have the same influence.
Its all in me book which will be out next year.

re genetic integrity. Sub-populations are more or less autonomous, youngsters follow scent trails from summer grounds at random in their second year, sometimes the third. Which means that most of the adults you see at a hibernation site were born somewhere else, i.e. another sub-population.
'I get my kicks on Route 62'
calumma
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Posted: 09 Oct 2009
Kevin

A few observations.

I very much welcome your proposed study. If you would like to chat
through details please don't hesitate to contact me directly.

I am often disheartened to hear land managers claim that what I
consider to be excessive management work can be proven to be
beneficial because of the (apparent) increase in adder observations the
following spring. There appears to be a basic lack of understanding
regarding detectability. Rarely are such draconian management regimes
adequately monitored.

It is important that you consider detectability when making comparisons
between areas. Capture-recaptre controls for differences in detectability,
but you may not be able to achieve the minimum sample sizes. Reliably
estimating reptile populations is very problematic and the available
methods require significant time investment. You may be better off
analysing presence data alone. Methods are available to help control for
detectability when analysing presence data.

I think you need to carefully consider your habitat variables when
assessing fragmentation. I think that Steve's recommendation to define
the area within a grid is the way to go. A grid has the additional
advantage that it would fit in with the presence based analysis. Size of
grid will depend upon the resolution of your available data and the
habitat variables that you decide to analyse. I envisage the development
of a site specific fragmentation coefficient that could then be compared
against presence data.   calumma40095.3771990741
Lee Brady
Kent Herpetofauna Recorder | Independent Ecological Consultant

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Vanderklam
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Joined: 20 Apr 2008
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Posted: 09 Oct 2009

Thanks for your comments Lee. At this point I would like to add that I have offered this project as a dissertation title to some degree students with the University of Chester, so hopefully they will be able to commit to longer field seasons than myself (dam work commitments!!). I agree that comparing presence data with site specific fragmentation co-efficient would be the way forward for the purpose of this study. My data thus far dates back 3-4 years depending on the sub-population, but hopefully my students will work on developing this over the coming years. I am fortunate in that landowners and habitat managers alike are keeping an open mind with regards to their methods of habitat management, and they are keen to take greater consideration of adders in the application of their methods. I would certainly be interested in discussing this further. Will you be attending the ARC-BHS Joint Scientific Meeting in December? Otherwise I could always email.

Best

Kev


Kevin Palmer
Lecturer in Animal Management/Course Manager
Reaseheath College
calumma
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Posted: 10 Oct 2009
Hoping to attend the meeting, but November to January events are all up in
the air due to an impending trip to Madagascar. Will you be attending the
NW Regional ARGUK Meeting in Leeds this month? I'm giving a presentation
there so its likely I will get to that one
Lee Brady
Kent Herpetofauna Recorder | Independent Ecological Consultant

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Vanderklam
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Posted: 10 Oct 2009

I have only recently moved up North, and have found little time to familiarise myself with such upcoming events, so probably not Im afraid. BUT just in case, do you have the dates and venue etcetc?? I should be at the ARC/BHS meeting though, so may well see you there!


Kevin Palmer
Lecturer in Animal Management/Course Manager
Reaseheath College
calumma
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Posted: 11 Oct 2009
Actually it's the Northern Meeting (not NW):

24 October. 10.15 am-4.00 pm. Northern Regional Conference, The
Lecture Theatre, Leeds Art Gallery, The Headrow, Leeds City Centre, LS1
3AA. Registration: ?17.50 including lunch (?12.50 concessionary)

Full details including a booking form are available on the
ARG UK website. calumma40097.423912037
Lee Brady
Kent Herpetofauna Recorder | Independent Ecological Consultant

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