By the end of winter, I'm interested in comparing the species diversity and density of 3-4 sites. The areas are all riparian, so the ground is not all the time flat.
For the moment I have planed the following design:
- 3 samples per site (near water, 2 m and 4 m from water)
- each sample in a plastic bag
- hand searching in the lab (it's time consuming but seems to be more efficient in collecting the bugs from the samples)
I'm still thinking on sample size (in many papers is usually one square meter) and how to choose the sampling site in order to be objective.
Suggestions / comments / or any other collecting protocol are gladly welcome.
Thank you!
It depends on what kind of bugs. Sifting always works better for arachnids in my experience.
Hello Ioan:
There are two standard sampling leaf litter methodologies used in comparing species diversity and density of soil arthropods. You can use Winkler bags. Winkler samples are an efficient method of sampling leaf litter arthropods. The method involves sifting bulk samples of leaf litter and rotten wood by agitating them vigorously in a bag above a coarse mesh screen. Litter arthropods are concentrated in the finer "siftate" that passes through the screen. Arthropods are then extracted from the siftate by a passive extraction method, in which the siftate is placed in thin mesh sacks and then suspended and enclosed within an outer cloth "Winkler bag." The Winkler bag tapers to a cup of ethanol. After loading the sample the Winkler bag is closed at the top and suspended in a sheltered location. Arthopods fall from the litter and accumulate in the ethanol, and the sample is taken off after 3 days. You can collect along a 100 m transect containing 25 quadrats (25 x 25 cm) at 5 m spacing in a parcel.
The second and most efficient method to collect soil arthropods are the Berlese funnels. Berlese funnels are used for extracting small arthropods (bugs, soil mites, collembola, coleoptera, ants etc.) from soil and litter samples. They work on the principle that insects and other arthropods that normally live in soil and litter will respond negatively to light. Therefore, a light source is used to force the arthropods to move downward, where they will fall into a funnel and then into a container of ethanol.
Soil and litter samples are first collected in a natural habitat, usually in a forested area. The samples may be sifted first so as to maximize the amount collected. You can collect leaf litter along a 100 m linear transect in 25 quadrats (25 x 25 cm) at 5 m spacing. Keep the leaf litter samples separated inside plastic bags for each quadrat and locality. Then in the lab put the samples inside the Berlese funnels during 3 days with a 25 watt light bulb to force down the arthropods into ethanol containers.
Good luck
Luis Miguel
OVerall, in Central Europe you will find more species of litter dwelling Heteroptera in dry/warm habitats, both in summer and even more during the winter months. So you might end up with very low numbers of both species and specimens when you are sampling at or very near the water. Also, depending on the terrain, two meters away from the water could mean sampling 2 meters in vertical or horizontal distance to the water body, so you might sample at very different microhabitats, which will mask any differences between "0", "2" and "4" meters distance, in particular when you are working at low species numbers.
Personnally I would visit a couple of sites, take some litter samples (use sifting to maximal your catch), and see what you get and how long it takes you. There is little point in planning some "standard" transect lines methods when you get nothing out of most subsamples. True bugs are very patchy in space and time. Also, it will be very difficult finding a stream where you can sample for 100 meters which constant abiotic conditions at the "2meter" mark.
The question whether it's better to use Winkler bags or Berlese funnels or sorting samples by hand is fare less important. FYI, I always sort through my samples by hand.
It might be better to use ground beetles instead, which have higher abundances and diversity and show narrow niches when it comes to riparian habitats. Or use both groups.
I would be interested in the results of your study.
Cheers
Claas
@Claas Damken.
I quit the initial ideea to do at 0/2/4 m because the sites were very variable, as you anticipated.
I took 3 random subsamples between 0 and 5 m from the river and I sorted the material in the lab. No surprise, Lygaeidae dominated the samples, the most frequent and most abundant genus was Scolopostethus. I found around 40 species but in low numbers. I did a sweep net collecting latter in the spring, in the same spots, and with only 100 sweeps (if the word is wright) I was able to collect the majority of the species collected on leaf litter.
The problem I encountered was: to wet litter... especially near the water, and in those samples I usually found less individuals or no individuals at al.
But overall it was an interesting experience, and I will repeat it next winter if there will be no snow.
@All
Thank you for your answers!
Best wishes,
Alex
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