Opiliones in Belgium - About the maps
(published VIII.2004)

How to read the maps

The present maps are based on 31581 individuals coming from 170 UTM-squares. That means that we still have a long way to go before we can offer the reader a complete map with all 387 boxes sampled. But there is more why the reader should be carefull in interpreting the maps.

All recent sampling effort comes from the Flemish part of Belgium. That makes that most of the 170 UTM squares are located in the northern part of the country, making our maps a bit top-heavy and suggesting a higher richness in this region than in the lower half. The reverse is probably true. Several interesting Opilionids (e.g. Amilenus aurantiacus, Lacinius horridus, Platybunus pinetorum) are only known from the south and more samples would yield a better knowledge about their occurrence and perhaps reveal still more species.

Map indicating the latest sample taken into account for each square.

To remind the reader of this skewness in the samples, this map is repeated as a background in all the species maps.

Almost all our data originate from pitfalls. Less than 1300 individuals out of our 31581 were captured by other means. Knowing that many species live above the ground in trees, pitfalls are probably not the best way to capture some species.
Dicranopalpus ramosus to name only one, never ends in a pitfall. Our sampling method is therefore skewed against this species and when reading the map we must take care not to come to wrong conclusions. The map is suggesting that D. ramosus is a rare Harvestman, but the species probably lives in much more squares.
Rilaena triangularis is the most common Harvestman in our area, but we wouldn't know were it not for a lucky coincidence. Eighty percent of our captures are juveniles. Adults only rarely stumble into pitfalls (graph shown with distribution map). The juveniles of most species aren't easily recognized, but the young R. triangularis crawl on the ground, are very active and easily identifiable. Based on the adults only we would think that R. triangularis was rare.

I did change the layout of the maps. If you look at the 1999-version you'll notice that I indicated each time range in which the species occured in that square. I now decided to give only the most recent find in each box. That is to counter the temptation to distill trends from the maps. Of our 31581 records only 831 are dated before 1980. The huge differences in sampling effort make any valid comparison between then and today impossible. The samples from 1980 and onward will form a good base for future trendstudies, however; at least in the northern part of the country.

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