The fate of the missing spores

It is well-known that many species with small diaspores can disperse far during extended temporal scales (many years). However, studies on short temporal scales usually only cover short distances (in, e.g., bryophytes up to 15 m). By using a novel experimental design, studying the realized dispersal, we extend this range by almost two orders of magnitude. We recorded establishment of the fast-growing moss Discelium nudum on introduced suitable substrates, placed around a translocated, sporulating mother colony. Around 2,000 pots with acidic clay were placed at different distances between 5 m and 600 m, in four directions, on a raised bog, with increased pot numbers with distance. The experiment was set up in April-May and the realized dispersal (number of colonized pots) was recorded in September. Close to the mother colony (up to 10 m), the mean colonization rates (ratio of colonized pots) exceeded 50%. At distances between 10 and 50 m colonization dropped sharply, but beyond 50 m the mean colonization rates stabilized and hardly changed (1-3%). The estimated density of spores causing establishments at the further distances (2-6 spores/m2) was realistic when compared to the estimated spore output from the central colonies. Our study supports calculations from earlier studies, limited to short distances, that a majority of the spores disperse beyond the nearest vicinity of a source. The even colonization pattern at further distances raises interesting questions about under what conditions spores are transported and deposited. However, it is clear that regular establishment is likely at the km-scale for this and many other species with similar spore output and dispersal mechanism

Är vi inne i det sjätte stora massutdöendet?

VAD ÄR ETT MASSUTDÖENDE? Ett massutdöende definieras som att minst tre fjärdedelar av arterna dör ut under en relativt kort tidsrymd, som kan vara från något år till några miljoner år. Sedan år 1500 har runt 1 procent av 77000 bedömda arter konstaterats utdöda. Till denna siffra ska hundratals beskrivna arter läggas som bedöms som sannolikt utdöda, och avsevärt fler som aldrig har beskrivits av vetenskapen. Försvinnandetakten av arter under de senaste 500 åren bedöms ha varit 100 till 1 000 gånger högre än den beräknade naturliga bakgrundsnivån, och den accelererar. De mest pessimistiska beräkningarna anger att 0,72 procent av djurarterna dör ut per år, vilket skulle leda till att vi når upp till tröskelvärdet för det sjätte massutdöendet redan år 2200. De tidigare massutdöendena under de senaste 540 miljoner åren tros ha orsakats av följderna av kontinentalförflyttningar, intensiv vulkanisk aktivitet och meteoritnedslag. Det nuvarande orsakas av människan