RAUK - Archived Forum - Carrying Capacities

This contains the Forum posts up until the end of March, 2011. Posts may be viewed but cannot be edited or replied to - nor can new posts be made. More recent posts can be seen on the new Forum at http://www.herpetofauna.co.uk/forum/

Forum Home

Carrying Capacities:

Author Message
Vicar
Senior Member
Joined: 02 Sep 2004
No. of posts: 1181


View other posts by Vicar
Posted: 07 Sep 2009
Hi Folks,

I'm trying to chase down research which has determined carrying capacities for our UK herps.

I know that figures will vary wildly, particularly with habitat type. E.g. I've seen figures for sand lizard which vary from 0.3 to 300 adults per hectare!

If I can do a trawl of the research to date, I may then be able to influence some targeted research...if necessary.

If you know of some figures, please post them up, Ideally with the reference, but I guess even non-referenced ideas are welcome. I can't seem to find any definitive figures.

Ta.

Steve Langham - Chairman    
Surrey Amphibian & Reptile Group (SARG).
herpetologic2
Senior Member
Joined: 15 Jun 2004
No. of posts: 1369


View other posts by herpetologic2
Posted: 07 Sep 2009
Hi Steve

I would suspect that the professional consultancy
business would have useful data which may help determine
estimated carrying capacities for each species in a
variety of different habitat types.

Volunteer surveys may also provide some idea as well

I have been surveying my local churchyard and I have had
up to 109 slowworms within a rough area of the graveyard
- technically rough undisturbed grassland - size 0.07Ha

From the survey information (collected from 20 felts) the
survey results for a hectare would be over 1500 animals!

Trapping of development sites would provide an idea of
the captured population. Now depending on how long and
how thorough the trapping is this would probably be the
closest to how many animals were within a particular
habitat.

At least something useful would come from mitigation
works.

The London Gateway project for example captured over
30,000 smooth newts in 2008. The density of smooth newts
for the whole site would be around 450 animals per Ha -
however the available habitat would be different to the
occupied habitat (i.e. the most suitable environs). These
areas of occupied habitat would have a higher carrying
capacity potentially. I suppose the mix of habitats would
produce an average figure.

How do you calculate the carrying capacity though?

I would be interested in helping with the research.

Jon





Vice Chair of ARG UK - self employed consultant -
visit ARG UK & Alresford Wildlife
Vicar
Senior Member
Joined: 02 Sep 2004
No. of posts: 1181


View other posts by Vicar
Posted: 07 Sep 2009
Hi Jon,

First step is to ensure the data isn't already there.

This year we've supported numerous PhD & MSc projects, and I can envisage roping off several 1 hectare plots, across various sites situated on known foci and otherwise. Then detailed mark-recapture with habitat analysis conducted over a prolonged period.

This is unlikely to provide a representative figure, but would help to scope the lower confidence limit. I think only destructive searches are likely to yield realistic figures.

Here's a 'starter for 10' - some based on literature, some plucked out of the air.

All figures are for the number of adult reptiles, occupying 1 hectare in 'average' habitat, but known to be present. Say in May (so we discount communal hibernacula)

Smooth snake: 20
Adder: 20
Grass snake: 20
Sand lizard: 100
Common lizard: 240
Slow worm: 600

Feel free to discuss.....

Vicar40063.7635763889
Steve Langham - Chairman    
Surrey Amphibian & Reptile Group (SARG).
GemmaJF
Admin Group
Joined: 25 Jan 2003
No. of posts: 2090


View other posts by GemmaJF
Posted: 07 Sep 2009

I think what would be interesting Steve is to consider what actually affects carrying capacity. Generally food supply is the one I hear quoted. I think only in exceptional circumstances does this represent a real limiting factor.. suitable 3D habitat structure and basking opportunity seem much higher on the list from my field observations. Clearly egg laying sites make a huge difference to Sand Lizard populations and soil types and structure have their influences on many of the widespread species, predation is another issue that influences observed numbers. Perhaps consider going for some sort of index for these essential features in the study else the 'average' carrying capacity is a little meaningless.

Regarding your figures none seem unreasonable for optimal type habitat, I'm not convinced it represents 'average' habitat but of course the terms are entirely subjective. One also has to consider that mobility of the species, intercepting 20 grass snakes in a hectare might be hard work, yet that hectare could easily be part of a larger picture for the species and actually be supporting far more animals that are not actually resident at any given time.


Gemma Fairchild, Independent Ecological Consultant
calumma
Senior Member
Joined: 27 Jun 2003
No. of posts: 351


View other posts by calumma
Posted: 08 Sep 2009
Steve

Just quickly. Agree with Gemma's points, although I think prey availability
can be an important issue on some sites (thinking about slow-worms and
molluscs for example).

Available data suggests that slow-worm densities can be much higher
than you have quoted. Even Jon's figure of 1500 is lower than some of my
own estimates. Certainly, Anne Riddell's surveys suggest that some sites
can support over 2000 animals per hectare.

There is of course an issue when estimating densities on small v large
sites.
Lee Brady
Kent Herpetofauna Recorder | Independent Ecological Consultant

Email
Vicar
Senior Member
Joined: 02 Sep 2004
No. of posts: 1181


View other posts by Vicar
Posted: 08 Sep 2009
[QUOTE=GemmaJF]

Regarding your figures none seem unreasonable for optimal type habitat, I'm not convinced it represents 'average' habitat but of course the terms are entirely subjective.[/QUOTE]

Heh, well I can actually define 'average' habitat objectively...for Surrey, at 1km grid fidelity.


here's an example for Ca

I know, that on average, for each occupied grid, I have two occupied hectares.

Your suggestion for modelling the CC for a hectare is, I think, sound. My trouble is, for trying to assess FCS at county-level, I'm never going to be able to gather the required data for widespread species.

I agree that the CC figures I've quoted seem on the high-side for average habitat. What I'd really like to avoid is using subjective values that 'feel' right. I'd rather go with endorsed figures derived from sound research...I wonder if there are any?


Steve Langham - Chairman    
Surrey Amphibian & Reptile Group (SARG).
herpetologic2
Senior Member
Joined: 15 Jun 2004
No. of posts: 1369


View other posts by herpetologic2
Posted: 10 Sep 2009
[QUOTE=Vicar]
Hi Jon,First step is to ensure the data isn't already
there.This year we've supported numerous PhD & MSc
projects, and I can envisage roping off several 1 hectare
plots, across various sites situated on known foci and
otherwise. Then detailed mark-recapture with habitat
analysis conducted over a prolonged period.This is
unlikely to provide a representative figure, but would
help to scope the lower confidence limit. I think only
destructive searches are likely to yield realistic
figures.Here's a 'starter for 10' - some based on
literature, some plucked out of the air.All figures are
for the number of adult reptiles, occupying 1 hectare in
'average' habitat, but known to be present. Say in May
(so we discount communal hibernacula)Smooth snake: 20
Adder: 20Grass snake: 20Sand lizard: 100Common lizard:
240Slow worm: 600Feel free to discuss.....
[/QUOTE]

Steve
I think that most people would agree with me that the
last thing we would want is seeing reptile habitat being
trapped out to answer this.

I would suggest that development led herpetofauna
mitigation sites would be best suited to providing such
information. The trapping of reptiles to remove them out
of the way of development would lead onto destructive
searches which would provide population data on reptile
sites across the country.

Have you approached any consultancies to look into this
avenue?

Some figures off the top of my head

3acre Brownfield site - Old car wreckers yard
Survey results - 30+ Slow-worms, 2 grass snakes, 15+
lizards
Trapping results
Slow-worms 700, Lizards 350, grass snakes 32, smooth
newts 750 and great crested newts 90

Canvey West - reptile survey results
Adder 6 and lizards 100
Trapping results - Adder 400+, Lizards 4,000+

Grassland site - 0.7Ha High density of anthills etc
Lizards - 48 mixed ages - peak count
Captured 747 lizards - 500 were young or newborn

Grazing meadow - 0.7Ha
Lizard - peak count 8
Captured - 96 lizards

Receptor site of above site - 1.3Ha
Survey results - 25 adults - total 62 animals
Estimated population 250 to 500 adults or 620 to
1240animals

I have lots of other sites where I can measure the site
total area and provide survey information along with
trapping figures

It shows you what the peak counts might reflect in the
captured populations.

J
Vice Chair of ARG UK - self employed consultant -
visit ARG UK & Alresford Wildlife
Vicar
Senior Member
Joined: 02 Sep 2004
No. of posts: 1181


View other posts by Vicar
Posted: 10 Sep 2009
Hi Jon,

That sort of information is incredibly useful!

With enough of that sort of information, I can do the stats to make it meaningful and useful.

I've got reasonable contacts across the industry...with the training programme and data searches etc so I'll definitely be chasing this up.

Is it something that IEEM could help with?

Steve Langham - Chairman    
Surrey Amphibian & Reptile Group (SARG).
herpetologic2
Senior Member
Joined: 15 Jun 2004
No. of posts: 1369


View other posts by herpetologic2
Posted: 12 Sep 2009
Hi Steve

I would definitely be up for following this up with IEEM
members.

This information can be obtained from consultants across
the country and it can be made anonymous -

At least we could put this data to good use to learn more
about reptiles and amphibians in the UK - I have several
past projects which I can review myself and I have
several future projects which can also be added into the
pot

Jon
Vice Chair of ARG UK - self employed consultant -
visit ARG UK & Alresford Wildlife

- Carrying Capacities

Content here