The combined effects of habitat fragmentation and life history traits on specialisation in lichen symbioses

Summary

Interactions between organisms are determined by life-history traits. Ecological strategies regarding species specialisation range from generalist to highly specialised relationships. Although it is expected that habitat fragmentation's effect on species abundance and survival depends on their degree of specialisation and life-history traits, few studies have delved into the interplay between interaction specialisation, life-history traits and habitat fragmentation.
Here, we investigate the combined effect of habitat fragmentation, forest structure and life-history traits (growth form and reproductive mode) on the specialisation of lichen-forming fungi (mycobionts) toward their photosynthetic partners (photobionts) in lichen symbioses.
We studied mycobiont specialisation in epiphytic lichen communities present in 10 fragments of Quercus rotundifolia forest embedded in an agricultural matrix. Both mycobionts and photobionts were identified DNA barcoding and mycobiont specialisation was measured through interaction parameters calculating the relative number of interactions (normalised degree; ND) and the specialisation of each species based on its discrimination from a random selection of partners (d'). Phylogenetic generalised linear mixed models were used to analyse the effect of patch size as well as the life history traits growth form (crustose, foliose, fruticose) and reproduction mode (sexual vs. asexual) on mycobiont specialisation.
Both mycobiont and photobiont richness along the patch size gradient followed a hump-back pattern, which was more pronounced in photobionts. Mycobionts forming crustose thalli established the largest number of interactions. Mycobiont specialisation (d') was larger for fruticose and foliose forms and species with vegetative reproduction. Along the gradient of fragment size, the relative number of interactions decreased and the specialisation of mycobionts with vegetative reproduction increased.
Synthesis. The study of mycobiont specialisation towards their photobionts in epiphytic lichen communities in a fragmented Mediterranean forest revealed a complex interaction between species' life history traits and habitat fragmentation. In particular, this interplay had a significant impact on the specialisation of mycobionts. The results show the ability of some species to modulate their specialisation according to habitat conditions, suggesting that some species may be more resilient to abiotic changes than expected.