Constancy and asynchrony of Osmoderma eremita populations in tree hollows

Abstract

A species rich beetle fauna is associated with old, hollow trees. Many of these species are regarded as endangered, but there is little understanding of the population structure and extinction risks of these species. In this study I show that one of the most endangered beetles, Osmoderma eremita, has a population structure which conforms to that of a metapopulation, with each tree possibly sustaining a local population. This was revealed by performing a mark-release-recapture experiment in 26 trees over a 5-year period. The spatial variability between trees was much greater than temporal variability between years. The population size was on average 11 adults tree-1 year-1, but differed widely between trees (0-85 adults tree -1 year -1 ). The population size in each tree varied moderately between years [mean coefficient of variation (C.V.)=0.51], but more widely than from sampling errors alone (P=0.008, Monte Carlo simulation). The population size variability in all trees combined, however, was not larger than expected from sampling errors alone in a constant population (C.V.=0.15, P=0.335, Monte Carlo simulation). Thus, the fluctuations of local populations cancel each other out when they are added together. This pattern can arise only when the fluctuations occur asynchronously between trees. The asynchrony of the fluctuations justifies the assumption usually made in metapopulation modelling, that local populations within a metapopulation fluctuate independently of one another. The asynchrony might greatly increase persistence time at the metapopulation level (per stand), compared to the local population level (per tree). The total population size of O. eremita in the study area was estimated to be 3,900 individuals. Other localities sustaining O. eremita are smaller in area, and most of these must be enlarged to allow long-term metapopulation persistence and to satisfy genetic considerations of the O. eremita populations.

Mark-recapture estimates of the survival and recapture rates of Cerambyx welensii Küster (Coleoptera cerambycidae) in a cork oak dehesa in Huelva (Spain)

“…However, adult insects avoid these unfavourable effects by restricting most of their activity to the nocturnal hours and taking shelter in holes or hollows during the day. In this way, they mimic the behavioural patterns of saproxylic insects [45], the life strategy of which adjusts to the environmental stability of their habitat [46][47][48]. The combination of a partly cavernous life and nocturnal activity habits additionally reduces the already small number of potential predators even in an environment close to such a highly biodiverse protected natural space as the Doñana National Park and Doñana Natural Park.…”

Restricted dispersal in a flying beetle assessed by telemetry

“…Thus, only one out of seven O. eremita individuals leave their natal tree according to these two independent studies. Even though the sex ratio in the trees is even, the number of captured females is always much smaller than that of males (Ranius 2001). This can be due to behavioural differences where females are occupied with egg-laying deep in the wood mould most of their adult life-time and only occasionally visit the wood mould surface to copulate, whereas males are more active near the wood mould surface with the pitfall traps trying to copulate.…”

“…One hollow tree can potentially sustain a local population with up to one hundred adults per year (Ranius 2001). There are asynchronous fluctuations in population size between trees, but the total metapopulation size is remarkably constant (Ranius 2001).…”

“…One hollow tree can potentially sustain a local population with up to one hundred adults per year (Ranius 2001). There are asynchronous fluctuations in population size between trees, but the total metapopulation size is remarkably constant (Ranius 2001). Using markrecapture, it has been estimated that 85 % of adult beetles remained in the natal tree throughout their entire life (Ranius and Hedin 2001).…”

High-accuracy sampling of saproxylic diversity indicators at regional scales with pheromones: The case of Elater ferrugineus (Coleoptera, Elateridae)

“…The overall agreement between pheromone traps and pitfall/window traps was relatively high, indicating that both systems have good detection rates and between them present a near complete picture of the true distribution of O. eremita. This implies that O. eremita is generally over-sampled relative to other species when using pitfall and window traps, where the pitfall traps placed inside the hollow trees usually have a high probability of catching O. eremita, likely due to its sedentary ecology (Ranius 2001, Ranius & Nilsson 1997; but see Chiari 2011, Chiari et al 2013. In the present study, single pheromone traps were placed according to a fixed centroid position at each site, but the accuracy of the system could presumably be improved further, with negligible added effort, by placing multiple traps per site using and close to large hollow trees.…”