Citation: Baur, B.; Rusterholz, H.-P.; Braschler, B. The Grassland Fragmentation Experiment in the Swiss Jura Mountains: A Synthesis. Diversity 2023, 15, 130. https:// doi.org/10.3390/d15020130 Academic Editor: Simona Maccherini Received: 25 November 2022 Revised: 13 January 2023 Accepted: 14 January 2023 Published: 18 January 2023 Copyright: © 2023 by the authors. Licensee MDPI, Basel, Switzerland. This article is an open access article distributed under the terms and conditions of the Creative Commons Attribution (CC BY) license (https:// creativecommons.org/licenses/by/ 4.0/). diversity Review The Grassland Fragmentation Experiment in the Swiss Jura Mountains: A Synthesis Bruno Baur *, Hans-Peter Rusterholz and Brigitte Braschler Department of Environmental Sciences, University of Basel, Bernoullistrasse 30, 4056 Basel, Switzerland * Correspondence: bruno.baur@unibas.ch Abstract: We synthesize findings from a 7-year fragmentation experiment in species-rich, nutrient- poor, dry calcareous grasslands in the north-western Jura mountains, Switzerland. We used a standardized approach with 48 fragments (0.25–20.25 m 2 ) and corresponding control plots in three sites. The 5-m-wide isolation area around the fragments was maintained by frequent mowing. Frag- ments experienced various ecological changes, e.g., plant biomass increased along fragment edges. We examined fragmentation effects on species richness and composition, abundance, genetic diversity, functional diversity, species traits and species interactions (pollination, herbivory, parasitism, disease) in a wide array of invertebrate (gastropods, spiders, woodlice, various insect groups) and plant taxa. Responses to fragmentation differed between taxonomical groups and species. While species richness and individual density were lower in fragments in some groups, the opposite was true for other groups. Fragmentation effects were most pronounced on species interactions; however, some effects only occurred with a delay. For example, fragmentation influenced foraging patterns of bumblebees, affecting pollination, which in turn resulted in a decreased outcrossing frequency and reduced genetic diversity in a focal plant species. We highlight key findings of the experiment and emphasize their implications for grassland conservation. Keywords: biodiversity; calcareous grasslands; environmental change; functional dispersion; habitat fragmentation; invertebrates; population dynamics; time lags 1. Introduction The current biodiversity loss due to environmental change is of great concern glob- ally [1,2]. Habitat fragmentation is generally considered to be one of the major drivers of this loss [1,3–6]. Fragmentation reduces the total area of original habitat, changes the environmental conditions in remnants, creates isolated subpopulations, disrupts individual behavior [7], interrupts the exchange of individuals and genes among populations [8], and alters species interactions [9] and ecological processes [10]. Thus, habitat fragmentation can influence an entire suite of processes, ranging from individual behavior through population dynamics to ecosystem fluxes. Habitat fragmentation occurs at different spatial scales [11,12]. It ranges from small breaks in otherwise homogeneous habitat to widely scattered fragments in a hostile ma- trix [13]. The relevant spatial scale is different for each species [14,15]. The response of a species to fragmentation depends on its dispersal ability, life history, and competitiveness, and on the type and size of the fragments, and the permeability for dispersing individuals of the matrix surrounding the fragment [4,16]. Large-scale fragmentation on the landscape level entails many challenges unfavorable to rigorous investigation. Habitat fragments in a landscape differ in size, shape, age (time since isolation), distance to large homogeneous habitat, and distance to other fragments: all of which make any proper replication of the investigation unit difficult [17]. Further- more, corresponding control areas are frequently lacking [18]. Experimental studies with Diversity 2023, 15, 130. https://doi.org/10.3390/d15020130 https://www.mdpi.com/journal/diversity