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Carrying Capacities: |
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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). |
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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 |
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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..... Steve Langham - Chairman
Surrey Amphibian & Reptile Group (SARG). |
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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 |
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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 |
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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). |
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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 |
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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). |
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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 |
