Alpine ecosystems, i.e. those above the elevation of the tree line, provide harsh living conditions for its inhabitants. Extreme temperatures, short growing seasons, low nutrient levels, high UV-radiation, and sometimes lack of moisture make organisms struggle for their existence. However, some species even thrive in these unhospitable regions. Yet, what we are seeing today is just a snapshot in time. The species composition was different in the past and will be different in the future.
“In order to understand how alpine communities are structured, how they vary across spatial and temporal scales, and how changes in the environment can affect their functioning, it is useful to describe a species or a community by the characteristics that determine how it functions ecologically,” PhD candidate Ruben Roos says.
Responses across gradients
“We know little about how non-vascular primary producer traits respond across environmental gradients, and whether their drivers differ from those of vascular plants,” Roos says.
“In addition, there is little knowledge about the associations of lichens and their traits with higher trophic levels such as micro-arthropods.”
Responses to climate change
Functional traits influence how an organism responds to its environment and how this can affect ecosystem processes.
“The use of functional traits, characteristics that determine a species’ ecological role, allows us to understand how these ecosystems will respond to current and future environmental change,” Roos says.
A trait may be color, when examining heat absorption, or an organism’s water holding capacity.
“This information helps us predict the possible future developments of ecosystems.”
What affects species turnover?
Roos has studied the importance of intraspecific variation versus species turnover as drivers of community-level traits across elevation for three different primary producer groups: vascular plants, bryophytes, and lichens.
“Their responses to their environment differ greatly between species, and sometimes even within a single species,” he says.
The fieldwork was carried out at Finse, on the Hardangervidda (Hardanger mountain plateau) in southern Norway.
Variation between groups and traits
“The importance of intraspecific variation differs between the groups, but also among traits,” he says.
Intraspecific variation was found to be the most important as driver of nutrient traits for vascular plants and lichens.
Water holding capacity is important
He has also explored the associations between mat-forming lichens and soil micro-arthropods. The results showed that mat-forming lichen species that differentially affect soil microclimate support different micro-arthropod abundances.
“Mat-forming lichens grown in mixture, often support higher abundances of micro-arthropods than expected from the individual components of the mixture.”
The abundance of arthropods at higher trophic levels depended more on lichen water holding capacity and prey availability than lichen diversity or identity.
Differences nine years later
Roos has assessed the recovery of soil micro-arthropods from experimental environmental change nine years after treatments were ceased.
“I found that there were large differences: Collembola and Mesostigmata recovered in terms of abundance, but the Collembola community compositions remained affected.”
The findings of these studies stress the importance of intraspecific variation as driver of community-level traits in different primary producers.
Roos defends his thesis “Functional traits across primary producer groups and their effects on micro-arthropod communities in alpine Norway”, Friday 20 September, 2019.