Variable Gene Dispersal Conditions and Spatial Deforestation Patterns Can Interact to Affect Tropical Tree Conservation Outcomes

Abstract

Tropical lowland rain forest (TLRF) biodiversity is under threat from anthropogenic factors including deforestation which creates forest fragments of different sizes that can further undergo various internal patterns of logging. Such interventions can modify previous equilibrium abundance and spatial distribution patterns of offspring recruitment and/or pollen dispersal. Little is known about how these aspects of deforestation and fragmentation might synergistically affect TLRF tree recovery demographics and population genetics in newly formed forest fragments. To investigate these TLRF anthropogenic disturbance processes we used the computer program NEWGARDEN (NG), which models spatially-explicit, individual-based plant populations, to simulate 10% deforestation in six different spatial logging patterns for the plant functional type of a long-lived TLRF canopy tree species. Further, each logging pattern was analyzed under nine varying patterns of offspring versus pollen dispersal distances that could have arisen post-fragmentation. Results indicated that gene dispersal condition (especially via offspring) had a greater effect on population growth and genetic diversity retention (explaining 98.5% and 88.8% of the variance respectively) than spatial logging pattern (0.2% and 4.7% respectively), with ‘Near’ distance dispersal maximizing population growth and genetic diversity relative to distant dispersal. Within logged regions of the fragment, deforestation patterns closer to fragment borders more often exhibited lower population recovery rates and founding genetic diversity retention relative to more centrally located logging. These results suggest newly isolated fragments have populations that are more sensitive to the way in which their offspring and pollen dispersers are affected than the spatial pattern in which subsequent logging occurs, and that large variation in the recovery rates of different TLRF tree species attributable to altered gene dispersal regimens will be a likely outcome of fragmentation. Conservation implications include possible manual interventions (manual manipulations of offspring dispersers and/or pollinators) in forest fragments to increase population recovery and genetic diversity retention.

Genetic Diversity of Dominant Plant Species in Tropical Land-Use Systems in Sumatra, Indonesia

“…In theory, consequences of habitat loss at the intraspecific diversity level are the loss of genetic diversity and increased differentiation of populations, caused by genetic drift, inbreeding and isolation by distance, and increased differentiation of populations, but not all empirical studies confirm this (A. T. Kramer, Ison, Ashley, & Howe, 2008;Lesser, Parchman, & Jackson, 2013;Sampson et al, 2014). The different consequences of population fragmentation for species are caused by different life history traits such as, gene flow, dispersal strategy, mating system, degree of isolation, and tree density of populations (Bacles & Jump, 2011;Breed et al, 2015;Ganzhorn, Perez-Sweeney, Thomas, Gaiotto, & Lewis, 2015;Jacquemyn, De Meester, Jongejans, & Honnay, 2012;Kashimshetty, Pelikan, & Rogstad, 2015;Kettle, 2014;Sebbenn et al, 2008). Thus, it is not advisable to develop conservation strategies of genetic resources for a plant community based on results of one or few species only.…”

“…The lack of information on genetic diversity, combined with different consequences of population fragmentation for various species (Kashimshetty et al., 2015) can result in inefficient management strategies to conserve plant communities. In an era of fast and vast land-use change in the tropics, an applicable and effective method for identifying biodiversity hotspots and determining protected areas is necessary (Ferraro et al., 2015; Lee, Garcia-Ulloa, & Koh, 2011; Reed, Sarasan, Kane, Bunn, & Pence, 2011).…”

Historic pollen and seed dispersal in fragmented populations of the two largest trees of the atlantic forest

“…[4][5][6] Deforestation and forest fragmentation of natural forests causes an environmental imbalance that results in irreversible consequences, such as the extinction of animal and plant species. 7 Without adequate intervention, deforestation and a lack of forest conservation can result in the disappearance of fragments over time. 7 The spatial isolation of tree species populations in small forest fragments reduces the number of reproductive individuals and may cause reproductive isolation by cutting off gene flow through pollen and seeds, which can affect genetic processes, such as genetic drift, mating systems, and natural selection.…”

“…7 Without adequate intervention, deforestation and a lack of forest conservation can result in the disappearance of fragments over time. 7 The spatial isolation of tree species populations in small forest fragments reduces the number of reproductive individuals and may cause reproductive isolation by cutting off gene flow through pollen and seeds, which can affect genetic processes, such as genetic drift, mating systems, and natural selection. 8 Such processes can decrease the genetic diversity and effective population size and increase the spatial genetic structure and inbreeding within populations, 9 eventually resulting in local extinction of tree species populations.…”

Plant genetic diversity in tropical lowland rainforest transformation systems in Sumatra (Indonesia)

“…However, investigations regarding changes in the genetic structure of tropical taxa due to fragmentation and habitat loss mainly rely on the information of single species compared in natural and unnatural habitats (Nason & Hamrick 1997;Torre et al 2008). Kashimshetty et al (2015) simulated different outcomes in population structure of different species after fragmentation events in tropical lowland rainforests. The results showed the high dependency on pollen dispersal, forest fragment size, logging frequency and life history of a species.…”