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Population biology and conservation of beetles and pseudoscorpions associated with hollow oaks

Ranius, Thomas LU (2000)
Abstract
Many species associated with old trees are threatened, as this habitat has decreased severely in Europe during the last 200 years. In old oaks, hollows with wood mould often form in the trunks and these harbour a specialized fauna mainly consisting of beetles, flies and pseudoscorpions. This thesis contains the first quantitative examination of the habitat requirements and population ecology of species belonging to this fauna.



The occurrence of many species were found to be correlated with tree characteristics related to the microclimate and the successional stage of the tree hollows. The species richness of beetles per oak was higher in plots that were originally open and were still grazed. Many species were harmed by... (More)
Many species associated with old trees are threatened, as this habitat has decreased severely in Europe during the last 200 years. In old oaks, hollows with wood mould often form in the trunks and these harbour a specialized fauna mainly consisting of beetles, flies and pseudoscorpions. This thesis contains the first quantitative examination of the habitat requirements and population ecology of species belonging to this fauna.



The occurrence of many species were found to be correlated with tree characteristics related to the microclimate and the successional stage of the tree hollows. The species richness of beetles per oak was higher in plots that were originally open and were still grazed. Many species were harmed by forest regrowth and, thus, to preserve the rarer fauna in old oaks it is important to continue the management of pasture woodlands.



The population dynamics were investigated on a certain species, Osmoderma eremita (Coleoptera: Scarabaeidae), within the framework set by metapopulation ecology. In O. eremita, the occupancy/tree was higher in larger stands than in smaller stands, but there was no correlation between occupancy/stand and isolation of stands. This suggests dispersal is important in the population processes within stands, but not between stands. O. eremita occurred in most of the larger stands and this probably mirrors the fact that the density of hollow oaks has been much higher in the area than today. A mark-release-recapture experiment on O. eremita was performed over five years. The population size in each tree varied moderately between years, whereas the population size variability in all trees combined was not larger than expected from sampling errors alone in a constant population. This indicates that the populations in each tree fluctuate independently of each other. The dispersals observed with mark-release-recapture occurred between trees situated 30–190 m from each other. As only a minor part of all dispersals are observed by mark-release-recapture, a simulation model was constructed to reveal the dispersal rate per individual. The model results suggest that 85% of the adults remain in the same tree throughout their entire life. This suggests that each hollow tree sustain a local population with limited connection with the populations in surrounding trees. Thus, the individuals of each tree could be seen as a local population, and the populations in all occupied trees in a stand together form a metapopulation.



A study on the genetic structure was carried out on Allochernes wideri (Pseudoscorpionida: Chernetidae) and Larca lata (Pseudoscorpionida: Garypidae). Both occur in hollow trees, but L. lata is a rarer and more specialized species than A. wideri. Among trees within a stand, the genetic differentiation was low but significant in A. wideri, whereas in L. lata, it was not deviating significantly from zero. This suggests the migration rate between neighbouring trees is high, in particular in L. lata, and thus we can reject the hypothesis that the low habitat occupancy observed in L. lata would be an effect of a low dispersal rate. (Less)
Abstract (Swedish)
Popular Abstract in Swedish

Eftersom gamla träd har blivit mycket ovanligare de senaste 200 åren, både i skogslandskapet och på ängs- och hagmarker, har djur som lever i gamla träd blivit mycket sällsyntare och många arter är utrotningshotade. I gamla ekar bildas ofta mulm i stammarnas håligheter. Mulmen består av murket trämjöl och i den lever en rik och specialiserad fauna som framför allt utgörs av skalbaggar, tvåvingar och klokrypare. I Sverige finns det mer gamla ekar kvar än i andra europeiska länder, så därför har vi ett internationellt ansvar för bevarandet av denna fauna. Detta är den första kvantitativa studien av faunan i gamla ekar som publicerats. Syftet har varit att bedöma hur olika arter påverkas av trädens... (More)
Popular Abstract in Swedish

Eftersom gamla träd har blivit mycket ovanligare de senaste 200 åren, både i skogslandskapet och på ängs- och hagmarker, har djur som lever i gamla träd blivit mycket sällsyntare och många arter är utrotningshotade. I gamla ekar bildas ofta mulm i stammarnas håligheter. Mulmen består av murket trämjöl och i den lever en rik och specialiserad fauna som framför allt utgörs av skalbaggar, tvåvingar och klokrypare. I Sverige finns det mer gamla ekar kvar än i andra europeiska länder, så därför har vi ett internationellt ansvar för bevarandet av denna fauna. Detta är den första kvantitativa studien av faunan i gamla ekar som publicerats. Syftet har varit att bedöma hur olika arter påverkas av trädens kvalitet och beståndens storlek och avstånd från varandra. Alla arter av vedskalbaggar och klokrypare som hittats i de undersökta träden har studerats. En utrotningshotad skalbagge, läderbaggen (Osmoderma eremita), har valts för mera ingående studier av populationsstorlekar, spridningen mellan träd och förekomsten i bestånd som varierar i storlek och avstånd från varandra. Två klokrypararter (gammelekklokryparen (Larca lata) och rötträklokryparen (Allochernes wideri)) har studerats genetiskt för att bedöma i vilken utsträckning djuren sprider sig mellan träden.



Läderbaggen har studerats genom att fallfällor satts upp i ekarnas håligheter fem år i följd i Bjärka-Säby, Östergötland. När läderbaggarna har fångats i fällorna så har de märkts och släppts ut igen. Datorsimularingar har utförts för att kunna utvärdera resultatet. Antalet läderbaggar varierar kraftigt mellan olika träd (0–85 fullbildade läderbaggar per år), men deras antal är av samma storleksordning från år till år. Individantalet i varje träd varierar oberoende av varandra, så det är inte något år som har varit särskilt bra eller dåligt för läderbaggarna i alla träd samtidigt. På detta sätt skiljer sig läderbaggen från de flesta andra insekter, som varierar kraftigt i antal från år till år, och ofta över stora regioner samtidigt beroende på väderförhållandena. De flesta läderbaggar (85%) stannar kvar i samma träd under hela sin livstid. Av dem som lämnar trädet flyger de flesta endast kortare sträckor.



I stora, sammanhängande bestånd förekommer läderbaggen i över hälften av träden, men i mindre bestånd är den ovanligare, även per träd räknat. Om hålträden finns i samma antal och placerade på samma sätt i framtiden som idag, kommer läderbaggarna att dö ut från det ena beståndet efter det andra av slumpmässiga skäl eller för att ekarna i bestånden tidvis blir olämpliga. Men läderbaggen har inte tillräcklig spridningsförmåga för att kolonisera bestånd med samma hastighet, och därför kommer den att försvinna från många regioner där den idag förekommer. För att läderbaggen skall kunna överleva på lång sikt räcker det därför inte med att bibehålla lokalerna som de ser ut idag, utan det krävs att små bestånd tillåts att bli betydligt större.



Klokrypare är små spindeldjur som saknar flygförmåga. Flera av dem lever i ihåliga träd och när de skall ta sig från ett träd till ett annat “liftar” de med flygande insekter. En studie av två klokryparearter med hjälp av enzymelektrofores visade att de genetiska skillnaderna var relativt små både mellan olika träd och olika bestånd. Det är ett tecken på att klokryparna sprider sig mycket mellan träd.



Skalbaggar och klokrypare förekommer mer i vissa hålträd än i andra, och det kan förklaras med att de föredrar träd med ett visst mikroklimat eller ett visst successionsstadium i nedbrytningen. Många arter föredrar grova träd som står solexponerat. När ekhagar växer igen missgynnar det många vedskalbaggsarter, förmodligen beroende på att mikroklimatet blir sämre när träden blir mer beskuggade. (Less)
Please use this url to cite or link to this publication:
author
supervisor
opponent
  • Professor Thomas, Chris D., Leeds
organization
publishing date
type
Thesis
publication status
published
subject
keywords
Systematic zoology, wood mould, tree hollow, pseudoscorpion, population variability, Osmoderma eremita, metapopulation, mark-recapture, habitat fragmentation, genetic structure, dispersal, beetle, computer simulation, taxonomy, zoogeography, Zoologisk systematik, djurgeografi
pages
116 pages
publisher
Department of Zoology, Lund University
defense location
Dep. Zoology, Helgonav. 3, Lund
defense date
2000-10-27 10:00:00
external identifiers
  • other:ISRN: LUNBDS/NBZY--00/1023--SE
ISBN
91-7874-053-3
language
English
LU publication?
yes
id
72f554d5-5d39-4dde-8034-d869dcb30f41 (old id 40927)
date added to LUP
2016-04-04 11:49:04
date last changed
2018-11-21 21:07:23
@phdthesis{72f554d5-5d39-4dde-8034-d869dcb30f41,
  abstract     = {{Many species associated with old trees are threatened, as this habitat has decreased severely in Europe during the last 200 years. In old oaks, hollows with wood mould often form in the trunks and these harbour a specialized fauna mainly consisting of beetles, flies and pseudoscorpions. This thesis contains the first quantitative examination of the habitat requirements and population ecology of species belonging to this fauna.<br/><br>
<br/><br>
The occurrence of many species were found to be correlated with tree characteristics related to the microclimate and the successional stage of the tree hollows. The species richness of beetles per oak was higher in plots that were originally open and were still grazed. Many species were harmed by forest regrowth and, thus, to preserve the rarer fauna in old oaks it is important to continue the management of pasture woodlands.<br/><br>
<br/><br>
The population dynamics were investigated on a certain species, Osmoderma eremita (Coleoptera: Scarabaeidae), within the framework set by metapopulation ecology. In O. eremita, the occupancy/tree was higher in larger stands than in smaller stands, but there was no correlation between occupancy/stand and isolation of stands. This suggests dispersal is important in the population processes within stands, but not between stands. O. eremita occurred in most of the larger stands and this probably mirrors the fact that the density of hollow oaks has been much higher in the area than today. A mark-release-recapture experiment on O. eremita was performed over five years. The population size in each tree varied moderately between years, whereas the population size variability in all trees combined was not larger than expected from sampling errors alone in a constant population. This indicates that the populations in each tree fluctuate independently of each other. The dispersals observed with mark-release-recapture occurred between trees situated 30–190 m from each other. As only a minor part of all dispersals are observed by mark-release-recapture, a simulation model was constructed to reveal the dispersal rate per individual. The model results suggest that 85% of the adults remain in the same tree throughout their entire life. This suggests that each hollow tree sustain a local population with limited connection with the populations in surrounding trees. Thus, the individuals of each tree could be seen as a local population, and the populations in all occupied trees in a stand together form a metapopulation.<br/><br>
<br/><br>
A study on the genetic structure was carried out on Allochernes wideri (Pseudoscorpionida: Chernetidae) and Larca lata (Pseudoscorpionida: Garypidae). Both occur in hollow trees, but L. lata is a rarer and more specialized species than A. wideri. Among trees within a stand, the genetic differentiation was low but significant in A. wideri, whereas in L. lata, it was not deviating significantly from zero. This suggests the migration rate between neighbouring trees is high, in particular in L. lata, and thus we can reject the hypothesis that the low habitat occupancy observed in L. lata would be an effect of a low dispersal rate.}},
  author       = {{Ranius, Thomas}},
  isbn         = {{91-7874-053-3}},
  keywords     = {{Systematic zoology; wood mould; tree hollow; pseudoscorpion; population variability; Osmoderma eremita; metapopulation; mark-recapture; habitat fragmentation; genetic structure; dispersal; beetle; computer simulation; taxonomy; zoogeography; Zoologisk systematik; djurgeografi}},
  language     = {{eng}},
  publisher    = {{Department of Zoology, Lund University}},
  school       = {{Lund University}},
  title        = {{Population biology and conservation of beetles and pseudoscorpions associated with hollow oaks}},
  year         = {{2000}},
}