Most of the world's land surface is currently under human use and natural habitats remain as fragmented and eroded samples of the original landscapes. Measuring the fitness of plants in these pervasive environments represents a fundamental endeavour for predicting the potential evolutionary capability response of remnant plant populations to currently ongoing anthropogenic changes. Research on genetic diversity and performance of progeny produced in fragmented landscapes has increased in the past decade. While response patterns show divergent results, there has not been an attempt to generalize global response patterns on plant progeny performance in fragmented habitats. Here we systematically reviewed the scientific literature to determine overall habitat fragmentation effects on progeny performance and on the genetic characteristics of the progeny as proxies of plant fitness.
Here, by means of hierarchical and phylogenetically-independent meta-analyses we review habitat fragmentation effects on the genetic and biological characteristics of progeny across 180 plant species. We assessed habitat fragmentation effects on early and late progeny performance parameters, genetic diversity, outcrossing rates, inbreeding coefficients and correlated paternity of the progeny. Furthermore, we evaluated whether life forms, pollen dispersal vectors and/or the mating systems of plants may drive differential responses of habitat fragmentation on progeny quality.
Results/Conclusions
We found that progeny sired in fragmented habitats has lower vigor, showing reduced germination, survival and growth. Habitat fragmentation significantly reduced progeny vigor of plants with different life forms and different pollen dispersal vectors, with the exception of vertebrate-pollinated plants. Habitat fragmentation had stronger negative effects on progeny vigor of outcrossing plants as compared to plants with mixed mating systems. Similarly, progeny generated in fragmented conditions showed overall genetic erosion, with decreased genetic diversity and outcrossing rates as well as increased inbreeding coefficients and correlated paternity. Genetic erosion in progeny was similar across plants with different mating systems. Habitat fragmentation had no effects on the genetic parameters of the progeny of plants pollinated by vertebrates. Our findings support theoretical expectations regarding the ecological and genetic consequences of reduced population sizes and increased isolation among populations. In demographic terms, such effects reveal a gloomy future for angiosperms remaining in fragmented habitats, since they indicate decreasing recruitment of plant populations, thereby increasing the probability of extinction. Should landscapes remain as they are now, without increasing the area and connectivity between natural habitats, we may expect a decreasing establishment of genetically depleted plant progeny in fragmented conditions with little long term viability.