What keeps ‘living dead’ alive: demography of a small and isolated population of Maculinea (= Phengaris) alcon

Abstract

Small and isolated populations are prone to future extinctions and thus perceived as 'living dead'. Although generally considered to be of low conservation value, their existence can still enhance species survival at the landscape scale through improving the connectivity of other populations and facilitating some (even if little) gene flow. We investigated the demography and genetic status of a tiny and highly isolated local population of Maculinea (= Phengaris) alcon near its distribution margin with the aim of identifying the features that allow it to persist. The study comprised intensive mark-recapture, surveys of Gentiana pneumonanthe foodplants and butterfly eggs laid on them, as well as genetic analyses. The population has been found to be characterised by low genetic diversity and estimated at only a few tens of individuals. The foodplant availability turned out to be the most obvious factor limiting M. alcon abundance. Nevertheless, the life expectancy of adult butterflies is fairly long, and their flight period very short, implying that most individuals occur within the same time window. Together with the relatively little protandry observed, i.e. almost synchronous emergence of males and females, this increases the chances of random mating among the individuals. Moreover, the butterflies move freely across the core habitat fragment. All things concerned, the effective population size is presumably not much lower than the recorded population size. Our findings provide guidelines for pinpointing those among 'living dead' populations that are likely to be the most persistent and thus worth conservation efforts aimed at preserving them.

A Unique Population in a Unique Area: The Alcon Blue Butterfly and Its Specific Parasitoid in the Białowieża Forest

“…The estimated life span of adults of P. alcon in our study (1.7 days) was relatively low but not exceptional if compared with available data [ 20 , 22 , 47 , 48 , 51 , 52 ], and Phengaris butterflies are generally considered short-lived insects (see [ 38 ]). Their short life expectancy is compensated for by high fecundity, and in the case of P. alcon a female can lay 19 eggs/h and 80–100 eggs per day [ 51 ].…”

“…Interestingly, the estimated life span (4.9 days) of another isolated population studied in the same region was nearly three times longer [ 22 ]. This discrepancy could be related to the high density of adults at the presently investigated site, which could trigger emigration [ 34 ] and therefore affect the recorded residency time.…”

“…As a consequence many individuals could leave the site relatively freely. In contrast, the previously studied population was very small and its site was surrounded by a clearly distinct biotope of wetlands with tall vegetation of sedges and Phragmites [ 22 ].…”

“…In the European lowlands the most common ecotype is that dependent on G. pneumonanthe. Quite often it exists in very small and spatially isolated local populations, however, large metapopulation systems with many connected populations are also known [ 16 , 17 , 18 , 19 , 20 , 21 , 22 ]. Two host ant races could be distinguished in Europe, i.e., north-western populations depending on Myrmica rubra and Myrmica ruginodis, while the remaining ones mostly exploit the nests of Myrmica scabrinodis [ 23 ].…”

Sexual differences in age-dependent survival and life span of adults in a natural butterfly population

“…36 ] and/or explored dispersal [for a review see 37 ] or movement within habitat patches [e.g. [38][39][40][41] ]. Less attention has been paid to survival analysis, and usually only time-dependency of survival was tested, i.e.…”