Effect of Herbage Density, Height and Age on Nutrient and Invertebrate Generalist Predator Abundance in Permanent and Temporary Pastures
Round 1
Reviewer 1 Report
Dear authors
Thank you for the significantly improved version of your manuscript. Unfortunately, I still have two major concerns i) you have to stick to your results for lycosids and carabids only (probably adapt/change the analysis accordingly) ii) the sampling design is problematic because you are defintely sampling an edge effect. You will have to give much more information about the neighbouring areas and elaborate on the difficulties of the interpretation in the discussion.
All the best
Comments for author File: 
Comments.pdf
Author Response
We thank the reviewer for their detailed and constructive comments on the paper. We have addressed each comment below.
Reviewer 1
Lines 27-28: Lycosids and carabids
AU: This has been changed throughout to make it clear that lycosid and carabid specimen numbers were recorded.
Line 82: With pitfall traps it is reall difficult to say something about population sizes, especially when you are working on family level only.
AU: Populations has been changed to abundance
Line 92: Which parameters exactly, what kind of resolution does the data have, and at which height?
AU: Further detail has been added: ‘Weather data (total daily rainfall and average daily values for temperature, windspeed, relative humidity and irradiance), were recorded at the site above ground level throughout the study.’ The weather station is above ground and we can’t access the site due to lockdown to specifically determine the height.
Line 97: Change 2019
AU: Corrected.
Line 110: Move to the second sentence of the paragraph
AU: Moved the field names to the second sentence as suggested.
Line 115: Thank you for providing the map. Unfortunately, I have to say that I am really worried regarding the sampling design of your study. You are clearly sampling edge effects and it will remian unclear if your collected data represents a difference in management, vegetation composition or the species pool of the neighbouring areas. I highly recommend to include a table/description containing information on the neighbouring areas. You will also have to include a paragraph about these limitations into the discussion, and tone down your statements regarding management and age of the fields in focus. Try to give as much as possible information on the neighbouring fields and discuss your results in the light of those.
AU: Further description of the field locations has been added from line 116 as “In the majority of cases, the fields studied were bordered by either a road, railway, tarmac footpath, waterway or arable field. Arable fields (south and east of fields C and D, and south of field F) included winter wheat, which received a single application of herbicide and inorganic fertilizer during the study period.” We acknowledge that the pitfall traps were in the margins of the fields as stated and shown, but this was required due to the field activities going on and to allow recording invertebrates. We have also added a paragraph to the discussion to acknowledge the potential weaknesses of the design from line 322 as “Additional years of sampling and during other periods of the year, rather than just 10-weeks in spring as in the current study, would help to confirm that the results are consistent over a longer time period. Also, while the location of the pitfall traps in the margins of each field helped avoid damage and disturbance from field activities (vehicles and animals), it may have influenced invertebrate abundance. Sampling of neighbouring fields would help address this issue. The presence of waterways, railway, roads and pathways next to fields studied would hopefully create a border from neighbouring areas.”
Line 138: That is the opposite of random.
AU: Randomly has been removed.
Line 155: You can only use the numbers for spiders and beetles which you exactly identified as lycosids or carabids. I would also recommend to not include juveniles unless you are 100% sure that these are lycosids. All the others have to be discarded. In the following you should refer only to lycosids and carabids throughout the manuscript.
AU: We were able to identify adult and juvenile lycosids and carabids. We have changed the general use of spiders and beetles throughout to lycosids and carabids as suggested, and to be clearer.
Line 255: Why are they important? Please elaborate and be more specific!
AU: This sentence at line 264 has been revised as “These areas are also known to be an important habitat for conserving invertebrate populations…”
Line 257: unclear
AU: This sentence at line 266 has been revised as “In this study, we present data on both productivity and presence of invertebrates of such a system through measuring biological properties of pastureland of different ages and at the same time recording the abundance of two predatory groups of invertebrate: namely lycosids and carabids.”
Line 260: Answer your research question first, and state if/how your results met your assumptions.
AU: This sentence has been moved to the start of the discussion.
Line 272: unfortunate choice of words
There should be references to spport your results
AU: Rephrased to “This would support the general finding of lower nutrient quality [5]” with a reference added.
Line 276: What does this reference contribute here? Does this study support your results? If so, please state how.
AU: Rephased as suggested to “As observed in the current study, Bell et al. [12] found that sugar and DOMD content of temporary ley pastures are not necessarily superior to more diverse and permanent pastures.”
Line 292: What are gound spiders? Do you mean ground beetles?
Again, you have to use the accurate terms! Please, refer only to lycosids and carabids.
AU: Spiders and beetles have been revised to lycosids and carabids throughout.
Line 293: That is correct, but please elaborate on the relationship of physical structure and spider number. Additionally, state clearly whether you are referring to species numbers oder specimen numbers of spiders.
AU: Further explantation has been add as “Taller and denser pastures also had greater abundance of lycosids, a finding that is not unexpected given previous work on associations between the physical structure (e.g. open vegetation and reduced sward height due to grazing) and lycosid specimen number (reviewed in Bell et al. [16] and Petillon et al [35]).”
Line 297: Yes, dispersal might be explain the differences. However, there are several other options. You are referring to absolute numbers of spiders and beetles, but you have to be aware that pitfall traps provide you with estimates of the activity abundance, not with absolute numbers. In your study you have the problem to work with data on family level. So the different numbers could be a result of the difference in activity abundance in two (or probably even more) lycosid species. The same might be true for the carabid beetles. Please, include some sentences about the pitfalls when using pitfall traps...
Check out:
Woodcock // Pitfall trapping in ecological studies
and literature cited within.
AU: Several sentences have been added to discuss pitfall traps and the sampling design and differences in life cycle as “Furthermore, the life cycle of Lycosids and Carabids are not the same. In early spring, male lycosids are more active than females, and females become more active towards the end of the spring [38]. For carabids, there are spring breeders that reproduce in spring or early summer, and autumn breeders that reproduce in summer or autumn [39]. Therefore, the timing of the current study would likely sample the lycosids and carabids that are more active in early spring. Pitfall traps are useful for assessing the relative abundance of ground dwelling lycosids and carabids to compare different areas over a short period [40], as in the current study. While the location of the pitfall traps in the margins of each field helped avoid damage and disturbance from field activities (vehicles and animals), it may have influenced records of invertebrate abundance. Sampling of neighbouring fields would have helped determine if sampling the margins of fields biased the results. The presence of waterways, railway, roads and pathways next to fields studied would hopefully create a barrier from neighbouring areas. Additional years of sampling and during other periods of the year, rather than just 10-weeks in spring as in the current study, would help to confirm that the results are consistent over a longer time period.”
Line 303: I am pretty sure, that you would find a pattern when you consider the structure/vegetation/landuse of the neighbouring areas. I highly recommend to include a paragraph about the possibility, that you sampled an edge effect.
AU: Explanation added to the end of the discussion as discussed above.
Line 307: Differences in life cycle of Insects and Arachnids should also be considered. Please, add a couple of sentences.
AU: Explanation added to the end of the discussion as discussed above.
Reviewer 2 Report
The authors have tried to address reviewer recommendations in this revised manuscript. Although I am still concerned about the study being done in only one year, I believe it could be published. I still think the authors could add a brief explanation about this shortcoming in their discussion. I like that they have indicated a "10-week study period", but they might include something about the importance of conducting this work over another time period.
Author Response
We thank the reviewer for their comments, which are addressed below.
Reviewer 2
The authors have tried to address reviewer recommendations in this revised manuscript. Although I am still concerned about the study being done in only one year, I believe it could be published. I still think the authors could add a brief explanation about this shortcoming in their discussion. I like that they have indicated a "10-week study period", but they might include something about the importance of conducting this work over another time period.
AU: We acknowledge the fact that the study was not repeated for another year and have added discussion in the final paragraph at line 322 to discuss the implications of the timing of the study as “Furthermore, the life cycle of Lycosids and Carabids are not the same. In early spring, male lycosids are more active than females, and females become more active towards the end of the spring [38]. For carabids, there are spring breeders that reproduce in spring or early summer, and autumn breeders that reproduce in summer or autumn [39]. Therefore, the timing of the current study would likely sample the lycosids and carabids that are more active in early spring. Pitfall traps are useful for assessing the relative abundance of ground dwelling lycosids and carabids to compare different areas over a short period [40], as in the current study. While the location of the pitfall traps in the margins of each field helped avoid damage and disturbance from field activities (vehicles and animals), it may have influenced records of invertebrate abundance. Sampling of neighbouring fields would have helped determine if sampling the margins of fields biased the results. The presence of waterways, railway, roads and pathways next to fields studied would hopefully create a barrier from neighbouring areas. Additional years of sampling and during other periods of the year, rather than just 10-weeks in spring as in the current study, would help to confirm that the results are consistent over a longer time period.”
This manuscript is a resubmission of an earlier submission. The following is a list of the peer review reports and author responses from that submission.
Round 1
Reviewer 1 Report
Dear authors
Thank you for this interesting study.
Unfortunately I have some major comments regarding almost all sections of the manuscript. While I think that the basic idea is interesting and more or less well described in the introduction. The description of some the used methods is flawed. My bigggest concern is the lack of sufficient identification work regarding the two different invertebrate groups, which in my opinion is mandatory to give statements regarding the feeding habits and habitat requirements of the two groups. The habitat requirements are important to fully understand the differences in abundance of these two invertebrate groups, and if one/both groups might possibly benefit from management/conservation strategies. Additionally, the discussion of the results is insufficient and would clearly benefit from a seperation from the results. The whole discussion section has to be extended and elaborated, and some basic literature is missing.
Comments for author File: Comments.pdf
Author Response
Reviewer 1
Lines 27-28: specimen or species numbers? Please, clarify here
AU: Added at Line 20 what spiders and beetles were observed: ‘(primarily lycosid species) and beetles (carabids) abundance’.
Line 53: pratense
AU: Corrected
Lines 72-73: What do you mean by landscape composition? Are you referring to the heterogeneity/structure within one landscape or different landscapes?
AU: Landscape composition has been changed to ‘the physical composition of the landscape’ to make this clearer as suggested at line 73. An additional three references are added here also; one very helpfully suggested by the reviewer (Bell et al 2001) as well as literature from Thomas et al (2003) and Batáry et al. 2008.
Lines 78-79: Can you please explicitly state your expectations and elaborate why you are having those. This is important to understand the rationale behind your study.
AU: This sentence has been extended at line 83 to elaborate further on the reason for the study: ‘to explore the balance between productivity and abundance of two different types of generalist predator groups – spiders and beetles’.
Lines 84-91: Do you have coordinates?
Can you please provide a simple map of the farm. In my opinion it is important to get an idea of the location and the distances between the different fields.
Why February and April? This seems counterintuitive as a lot of grasses are not flowering during spring and invertebrate activity usually also peaks later in the year, when it is warmer. Elaborate!
Did you measure these data yourself or do you have an external source? In case you measured them yourself please elaborate on and specify your measuring devices.
AU: Coordinates have been added to line 88.
Figure 2 is a map of the farm (line 114) showing fields monitored.
A sentence (lines 89-92) has been added to justify the period studied: ‘This period was studied as it covered the transition between winter (when grass is rested from grazing) and more productive spring grass growth (when productivity is high and grass is utilized for forage) as ambient temperatures increase (Figure 1).’
A sentence has been added (line 92) to clarify that weather data is recorded by the university weather station: ‘Weather data was recorded at the site throughout the study.’
Line 95: Do I understand correctly that the data for 2019 is part of the ten year average data from 2009-2019? If this is the case I would suggest to rather exclude them and simply check the years 2009-2018 in comparison to 2019. That will give you a much clearer picture of the conditions.
AU: That has been corrected, it should be 2009 to 2018.
Lines 126-127: How did you randomly pick the sites? Random coordinates? When you write that certain spots were avoided, this is the opposite of random.
AU: This has been revised (lines 137 – 139) to be clearer that the ring was randomly placed at each point of a W within each field: ‘In each field five grass samples were cut to ground level and within a 36 cm diameter wire ring (0.1 m2) randomly placed on the ground at each point of a W-pattern walked across the field. The W-pattern ensured representative coverage of each field [19].’ The NIRS machine is calibrated to work on fresh grass and not other material.
Lines 143-145: How? I assume, you counted the specimen per species (activity abundance).
Who did the identification, which keys were used, was every individual indentified to species level. What about juvenile specimen?
AU: We have added further information (lines 156-159) here to indicate what we identified and how: ‘As a measure of generalist predators, the number of adult and juvenile spiders and beetles were counted in a pitfall trap (Figure 3) were recorded for each field each week. Spiders (primarily lycosids) were identified to family level using the guides of Roberts (1995) and Bee et al. (2017) and beetles (carabids) using (Chinery, 1993)’.
I don´t understand this design. Can you please provide a simple map and the respective locations for the traps. I am worried that you sampled an "edge effect" rather than sampling the respective number for the single fields.
AU: A map has been added at line 114 figure 2 as mentioned above. Yes the traps on the edge of fields was more to avoid field operations but still carry out the study – this can still be problematic and careful monitoring is needed.
Lines 148-149: Even when I look at the drwaing I don`t understand what exactly you need the two pots for. Additionally, how do the beetles know that they have to go under the upper pot?
AU: The use of two pots aided the collection of spiders and beetles based on their different preferences. Further explanation has been added to lines 164 to 168 to clarify this: ‘The use of two pots aided the collection and separation of allowed spiders and beetles, as spiders gathered in the upper pot and beetles preferred the darkness of the lower pot, as highlighted in Figure 3. The average number of spiders and beetles per pot for each field and week of the study was used in the analysis.’ This approach appeared to work well in the agricultural fields studied to monitor spiders and beetles.
Line 169: Species number?
Specimen number?
Honestly, for me it is really difficult to understand what exactly you are testing here. I am not saying it is wrong, I simply have difficulties understanding the given procedure.
AU: Further detail has been added to lines 190: ‘where Yijk is the dependent variable of average herbage nutrient concentration, spider or beetle specimen numbers per pot for each field.’
Line 177: Please split this up into a results and a discussion section. While the results section might be sufficient, the discussion section has severe limitations regarding the different habitat requirements of beetles and spiders, and the dispersal capacities. Additionally, there is a large amount of literature addressing the same research questions, which should be acknowledged, and ussed to strengthen your argumentation. For some of the addressed topics in the discussion, an identification down to species level would be appropriate.
AU: The results and discussion sections have been split as suggested. Further literature and detail has been added as suggested.
Line 179-180: In my opinion the results part should only include your own results, supported by figures & tables, and no references. This sentence can be placed in the introduction/discussion.
AU: The results and discussion sections have been split as suggested.
Lines 184-186: Please move this to the discussion section.
AU: This has been moved to discussion as suggested.
Table 2 One can easily assume that spiders and juvenile spiders are general predators, that stands the case for every single species.
Beetles, however, are an order of insects that contains various groups with a large variety of feeding habits. Sometimes feeding habits even differ between larvae and imago stages. In order to get a slight idea of the feeding habits, the beetles have to be at least identified down to family level!
AU: Further detail to the identification of spiders and beetles has been added at line 156 as described above. They were identified to family level.
Lines 204-205: Since you do not make any differentiation between the different beetle families this statement is really difficult. Even though, e.g. carabid beetles are running on the ground, the species still have wings, which technically allows them to fly. In addition, one can assume that beetles might cover large distances in these relatively simple environments.
AU: This is a really good point and we now try to make more explicitly clear in our study that our findings show that beetles and spiders are influenced differently by the variables examined here (e.g. sward height) although this does not of course in itself mean that individual groups (spiders or beetles) behave in a completely homogeneous way.
Line 237: Yes, this is a long knwon phenomenon that spider distribution and appearance is bound to vegetaion structure mostly. Schäfer (1970) was probably the first one to systematically study this (SCHAEFER, M., 1970: Einfluß der Raumstruktur in Landschaften der Meeresküste auf das Verteilungsmuster der Tierwelt.- Zool. Jb. Syst. 97: 55-124.), and he has been cited many times since then. Beetles, however, are obviously more prone to microclimate.
My question would be what is so interesting when you compare two groups of invertebrates from different orders (Arachnids & Insects)?
AU: This is a really good point and one that we now try to make more explicit in our study, namely that these two groups behave differently.
Line 243: For spiders this is absolutely not important. They don`t care which plant species they are sitting on, the only thing that is important is the sturcture of the plant and the habitat it provides.
AU: We agree and we now make it more explicit that physical structure is expected to be strong determinant of spider abundance in both our introduction, and also our discussion. We expand upon the literature already cited to include a wider range of references including:
Bell, J. R., Wheater, C. P., & Cullen, W. R. (2001): The implications of grassland and heathland management for the conservation of spider communities: a review. Journal of Zoology 255,377-387
Petillon, J., Georges, A., Canard, A., & Ysnel, F. (2007): Impact of cutting and sheep grazing on ground–active spiders and carabids in intertidal salt marshes (Western France) Animal Biodiversity and Conservation. 30, 201-209.
Gallé, R., Samu, F., Zsigmond, A., Gallé-Szpisjak, N. & Urák, I. (2019) Even the smallest habitat patch matters: on the fauna of peat bogs. J Insect Conserv 23, 699–705 (2019).
Lines 248-253: The study addresses some interesting
AU: We presume this is a supportive comment, which is appreciated.
Line 260: There is lack of literature regarding the influence of conservation on community structure in spiders and beetles. I will give just a few examples, but there is plenty of material:
Peter Dennis, John Skartveit, Anja Kunaver, David I. McCracken (2015):
The response of spider (Araneae) assemblages to structural heterogeneity and prey abundance in sub-montane vegetation modified by conservation grazing. // Global Ecology and Conservation.
Bell, J. R., Wheater, C. P., & Cullen, W. R. (2001): The implications of grassland and heathland management for the conservation of spider communities: a review. // Journal of Zoology.
Benton, T. G., Vickery, J. A., & Wilson, J. D. (2003): Farmland biodiversity: is habitat heterogeneity the key?. // Trends in ecology & evolution.
Dennis, P., Young, M. R., & Gordon, I. J. (1998): Distribution and abundance of small insects and arachnids in relation to structural heterogeneity of grazed, indigenous grasslands. // Ecological Entomology.
Petillon, J., Georges, A., Canard, A., & Ysnel, F. (2007): Impact of cutting and sheep grazing on ground–active spiders and carabids in intertidal salt marshes (Western France). // Animal Biodiversity and Conservation.
AU: We acknowledge that there is a wealth of literature on this subject and we now include several of these references that were suggested in our manuscript (Bell, Benton, Petillon,). We also include other work by Galle and colleagues, by Thomas et al. and by Wolz et al. that look at host traits such as dispersal ability, and also the landscape vs local factors that could be important in influencing spider abundance and diversity. We also acknowledge, however, the limitations of our study, which was restricted in its power to assess details about community composition. Our work however does clearly indicate that even on a local scale, a difference is observed between two different types of predatory arthropod can be observed. Heterogeneity amongst our sites indicates that whilst there are significant effects of measured factors such as vegetation height, nonetheless there are additional local effects that may be important for both of these.
Reviewer 2 Report
This paper briefly describes an experiment evaluating various physical and qualitative aspects of short-term (1-2 years) and permanent pastures and their relationship to invertebrate predator abundance. While the work is relatively well done, I do have some concerns with the experiment and the manuscript in its current form.
My major concerns are:
- Lack of replication in time. Why was this work done only one year, and in that one year it was only carried out during a 10-week period from February through April? This time period may be when the grasses and the clovers are very actively growing, but I think it would and should extend beyond this time. With the annual variability in temperature and precipitation, I can’t imagine doing this study for less than two years. Furthermore, while I am not an entomologist, I think this time period is too short to adequately evaluate the insects involved.
- Age of the temporary stands. The authors note that temporary stands in the UK are typically replaced within 5 years of sowing (line 51), and yet the stands studied here were either one or two years old. This would miss the latter three years of many stands, years where the stand productivity would likely increase (at least for 1-2 years) and then perhaps start to decline. Short-term (<5) stands often show this type of pattern. However, this would be missed in this study.
Of more minor importance, I do wonder what amount of previous year’s growth was included in samples from the sampled year since the sward was cut to ground level (line 126).
Author Response
Reviewer 2
This paper briefly describes an experiment evaluating various physical and qualitative aspects of short-term (1-2 years) and permanent pastures and their relationship to invertebrate predator abundance. While the work is relatively well done, I do have some concerns with the experiment and the manuscript in its current form.
My major concerns are:
Lack of replication in time. Why was this work done only one year, and in that one year it was only carried out during a 10-week period from February through April? This time period may be when the grasses and the clovers are very actively growing, but I think it would and should extend beyond this time. With the annual variability in temperature and precipitation, I can’t imagine doing this study for less than two years. Furthermore, while I am not an entomologist, I think this time period is too short to adequately evaluate the insects involved.
AU: Further detail regarding the chosen period studied has been added at lines 89 to 92: ‘This period was studied as it covered the transition between winter (when grass is rested from grazing) and more productive spring grass growth (when productivity is high and grass is utilized for forage) as ambient temperatures increase (Figure 1). This period was studied as it covered the transition between winter (when grass is rested from grazing) and more productive spring grass growth (when productivity is high and grass is utilized for forage) as ambient temperatures increase (Figure 1).’ The study was actually conducted by a visiting Masters student (as acknowledged) and therefore we were sadly limited in the longevity of the study. Yes we agree it would have been nice to repeat the study in another year if it was possible.
Age of the temporary stands. The authors note that temporary stands in the UK are typically replaced within 5 years of sowing (line 51), and yet the stands studied here were either one or two years old. This would miss the latter three years of many stands, years where the stand productivity would likely increase (at least for 1-2 years) and then perhaps start to decline. Short-term (<5) stands often show this type of pattern. However, this would be missed in this study.
AU: This has been corrected at line 111 as the temporary leys grown are high yielding for forage production and are actually replaced after only 2 or 3 years as part of a rotation – some are already replaced since the study.
Of more minor importance, I do wonder what amount of previous year’s growth was included in samples from the sampled year since the sward was cut to ground level (line 126).
AU: The fields were grazed by sheep over the winter months to remove some of the plant from the previous year as stated at line 121. The fields were then rested before the study.
Reviewer 3 Report
Minor revision for scientific note or short paper. Needs replications for scientific study.
Comments for author File: Comments.pdf
Author Response
Reviewer 3
Minor revision for scientific note or short paper. Needs replications for scientific study.
AU: The authors acknowledged that replication would be preferable but this was not possible on this occasion. Some of the temporary fields studied have now been replaced.
Line 51: Remove older
AU: Removed as suggested.
Line 128: Change 10
AU: Changed to ten as suggested.
Line 137: Remove ‘of each week’
AU: Removed as suggested.
Line 140: Remove ‘and’.
AU: Removed as suggested.
Line 143: Change pasture to grass.
AU: Changed as suggested.
Line 154: Change are to were
AU: Changed as suggested.
Line 160: Move ‘each week’ to the end of the sentence.
AU: Moved as suggested.
Line 161: Change ‘roughly’ to approximately.
AU: Changed as suggested.
Line 185: Change ‘records’ to ‘samples’.
AU: Kept records as this is the weekly dataset analysed and not the grass samples.
Line 271: Add comma after ‘systems’.
AU: Comma added as suggested but sentence moved to separate discussion section as requested by reviewer 1.
Line 205: Add comma.
AU: Comma added after ‘52%’ as suggested.
Line 309: Move ‘sward’ to before ‘age’
AU: Moved as suggested. Sentence has been moved to discussion.
Line 3030: Change ‘high’ to ‘higher’.
AU: Changed as suggested.
Line 316: Add ‘over a ten week period’ to the end of the sentence.
AU: Added as suggested.
Line 318: Changed ‘enhance’ to ‘had higher’.
AU: Changed as suggested.
