The impact of ecological interactions & population size on fitness traits & conservation in a perennial herb, Arabis alpina

Abstract

1. Conservation biology has traditionally neglected evolutionary processes, which are however fundamental in both the emergence and maintenance of biodiversity. Understanding adaptation can further allow
conservationist to make predictions for species responses to changing environments which are vulnerable to climate change, such as mountain areas.
2. The size of a population is often important for its viability. In plants, it can relate directly to fitness components and the ability of populations to respond adaptively to changing interspecific
interactions, such as those with pollinators and herbivores. Abiotic factors, such as altitude, may also be involved in the interplay of selection in plants.
3. The aim of this study was to test whether a perennial herb inhibiting mountain areas exhibits variation in traits related to fitness and interactions with mutualists and antagonists, as well as to test
whether this variation is related to population size and altitude or, instead, if it is directly related to plant-insect interactions.
4. I used the alpine rock-cress Arabis alpina (Brassicaceae) and combined field studies measuring reproductive fitness, pollen limitation, floral size and herbivory in 12 population in the self-
incompatible areas of the distribution, with common-garden experiments measuring nectar volume in 15 populations also originating from the self-incompatible areas, as well as herbivore performance
experiments in 6 populations representing different mating systems.
5. Results from the natural populations provided evidence contrary to the prediction that small populations or populations on higher altitude should suffer from inbreeding depression. Moreover, a minority
of the populations were pollen limited and as predicted, they were associated with higher altitudes. Overall, regional differences in the observed patterns from the field were sometimes found,
highlighting the importance of scale when making conclusions about the ecological behavior of a species.
6. Results from the common garden regarding nectar volume showed that floral size is an honest signal, as there was a positive correlation between floral size and nectar volume within most populations.
7. The larval performance experiment showed significant differences between populations in both larval survival and performance, reflecting variation in herbivory resistance which can potentially be
explained by differences in mating system.
8. Synthesis. This study demonstrates that an alpine plant can exhibit intraspecific variation in fitness-related traits important for interactions with mutualists and antagonists, as well as the way those
traits behave in relation to abiotic and biotic factors. Such variation is important to consider when implementing conservation actions and defining management units.

Popular Abstract

The impact of ecological interactions & population size on fitness traits & conservation in a perennial herb

When implementing conservation actions, it is easy to forget that species are not static entities, but they can instead respond to changes adaptively. In fact, much of biodiversity is distributed within species, and different populations can show tremendous variation in traits and behavior, of importance for conservation decisions. In addition, larger populations have a better chance to adapt to new conditions. This might be of great importance in the face of climate change, and especially on the most vulnerable areas, such as mountains.

In my project, I explored how population size and altitude influence factors that are important for the plant’s fitness, using the perennial plant Arabis alpina. One of these factors was seed production as an estimate for the plant’s reproductive fitness. If small and fragmented populations are inbred, they would suffer from lower fitness. In my study areas, Greece and Italy, I found no evidence of reduced reproductive fitness in smaller populations, or populations at higher elevations, therefore, no sign of inbreeding depression.

Another factor which is valuable to measure in animal-pollinated plant populations is pollen limitation. Pollen limitation describes how much more seeds a plant would have produced if it was pollinated at its maximal capacity, and thus reflects the population’s need for pollinators. I found that populations at higher elevations were more prone to pollen limitation. Still, most of the populations I visited appeared to be adequately pollinated by the local insect communities. Some of these trends could be linked to variation in floral size, which is an important plant advertisement for pollinators. In one of the two regions, pollen limited populations also had larger flowers, an investment that possibly reflects their high need to attract pollinators.

Besides pollinators, plants are frequently affected by herbivores. I performed a common-garden experiment using a butterfly herbivore (Pieris napi larvae) and I found that different populations of A. alpina from 6 locations spread across Europe have different defense levels against herbivory. Populations that were dependent on pollinators for reproduction were better defended than populations that could be fertilized by their own pollen, possibly reflecting that self-fertilization comes with a cost for herbivore defense. When I tried to measure herbivory damage between populations dependent on pollinators for reproduction in nature, I found only small differences.

Overall, my project increases our understanding of how variation within a species reflects evolutionary processes acting differently across parts of the species distribution. At the same time, a large proportion of the variation could not be explained by variation in population size or altitude, indicating that there is much more to learn on the factors affecting plant populations in mountain regions. The viability of a population depends on both the species’ biology but also on the interactions of the species with its local environment. Considering variation in these elements might be the only way to identify the processes of importance for protecting species as climate change is accelerating.

Master’s Degree Project in Conservation Biology; 60 credits; 2020
Department of Biology, Lund University

Advisors: Hampus Petrén & Magne Friberg
Biodiversity Unit, Department of Biology, Lund University

• author: Boutsi, Sotiria
• supervisor: Magne Friberg; Hampus Petrén
• organization: Degree Projects in Biology
• course: BION03 20191
• year: 2020
• type: H2 - Master's Degree (Two Years)
• subject: Biology and Life Sciences
• language: English
• id: 9028155
• date added to LUP: 2020-09-03 14:09:12
• date last changed: 2020-09-03 14:09:12