Journal of Ecology 2012, 100, 76–87 doi: 10.1111/j.1365-2745.2011.01919.x
CENTENARY SYMPOSIUM SPECIAL FEATURE Evolutionary changes in plant reproductive traits following habitat fragmentation and their consequences for population fitness
Hans Jacquemyn1*, Luc De Meester2, Eelke Jongejans3 and Olivier Honnay1
1Laboratory of Plant Ecology, University of Leuven, Arenbergpark 31, B-3001 Heverlee, Belgium; 2Laboratory of Aquatic Ecology and Evolutionary Biology, University of Leuven, Charles Deberiotstraat 32, B-3000 Leuven, Belgium; and 3Institute for Water and Wetland Research, Department of Experimental Plant Ecology, Radboud University Nijmegen, Heyendaalseweg 135, 6525 AJ, Nijmegen, The Netherlands
Summary 1. The effects of habitat fragmentation on plant population genetic structure and diversity are rela- tively well studied. Yet, most of these studies used molecular tools focusing on neutral genetic mark- ers, and much less is known about the potential evolutionary consequences of habitat fragmentation on ecologically relevant plant traits. 2. It can be expected that the altered biotic and abiotic conditions and limited gene flow following habitat fragmentation may impose strong selection pressures on traits important for plant fitness. Responses to these selection pressures may, however, be hampered by reduced genetic diversity through genetic drift. Conversely, evolutionary changes in flower or dispersal traits may itself impact the strength of inbreeding and genetic drift. 3. In this review, we highlight different reproductive plant traits that may be under selection follow- ing habitat fragmentation, and we examine studies that have shown indications for rapid evolution- ary responses. 4. There are still relatively few studies that have convincingly shown that habitat fragmentation generates rapid evolutionary responses. Separating genetic from plastic trait responses and quanti- fying the long-term fitness consequences of evolutionary changes in plant traits also remain major challenges. 5. Synthesis. Many plant traits may be subject to selection following habitat fragmentation, but, until now, studies that quantified evolutionary responses to habitat fragmentation are limited. To study the consequences of changing plant traits for population fitness, we advocate applying popu- lation models that link demographic vital rates, the responding plant traits and their heritability. Key-words: dispersal, habitat fragmentation, mating system, nectar, phenotypic variation, population dynamics, selection
genetics and long-term viability of the residing plant species Introduction (Honnay et al. 2005; Broadhurst & Young 2007). Habitat loss and fragmentation, together with climate The population biological consequences of habitat fragmen- change, environmental degradation through pollution, the tation are driven by both direct and indirect effects of changes invasion of exotic species and overexploitation, are consid- in population size and isolation. In a direct way, decreased ered to be the most important threats to biodiversity population size may lead to the loss of alleles through genetic world-wide (Diamond 1989; Pimm & Raven 2000). The drift, and to increased homozygosity through inbreeding disintegration of large tracts of natural habitat into many (Wright 1931, Young, Boyle & Brown 1996) (Fig. 1, arrow 1). small and spatially isolated fragments has major and well- The increased spatial isolation may hamper gene flow between documented consequences for the population biology, plant populations and may therefore prevent the replenish- ment of alleles lost through drift, thereby increasing genetic dif- ferentiation between populations (Wright 1931; Franklin *Correspondence author. E-mail: [email protected] 1980). The impact of habitat fragmentation on population