Abstract
Research Highlights: Frugivores able to disperse large seeds over large distances are indispensable for seedling recruitment, colonization and regeneration of tropical forests. Understanding their effectiveness as seed dispersal agents in degraded habitat is becoming a pressing issue because of escalating anthropogenic disturbance. Although of paramount importance in the matter, animal behaviour’s influence on seed shadows (i.e., seed deposition pattern of a plant population) is difficult to evaluate by direct observations. Background and Objectives: We illustrated a modeling approach of seed shadows incorporating field-collected data on a troop of northern pigtailed macaques (Macaca leonina) inhabiting a degraded forest fragment in Thailand, by implementing a mechanistic model of seed deposition with random components. Materials and Methods: We parameterized the mechanistic model of seed deposition with macaque feeding behavior (i.e., consumed fruit species, seed treatments), gut and cheek pouch retention time, location of feeding and sleeping sites, monthly photoperiod and movement patterns based on monthly native fruit availability using Hidden Markov models (HMM). Results: We found that northern pigtailed macaques dispersed at least 5.5% of the seeds into plantation forests, with a majority of medium- to large-seeded species across large distances (mean > 500 m, maximum range of 2300 m), promoting genetic mixing and colonization of plantation forests. Additionally, the macaques produced complementary seed shadows, with a sparse distribution of seeds spat out locally (mean >50 m, maximum range of 870 m) that probably ensures seedling recruitment of the immediate plant populations. Conclusions: Macaques’ large dispersal distance reliability is often underestimated and overlooked; however, their behavioral flexibility places them among the last remaining dispersers of large seeds in disturbed habitats. Our study shows that this taxon is likely to maintain significant seed dispersal services and promote forest regeneration in degraded forest fragments.
Highlights
Anthropogenic disturbance is so prevalent that no pristine ecosystem remains across the world.Primary tropical forest loss and degradation due to agriculture, plantations and infrastructural conversions, are the driving forces of a massive tropical biodiversity crisis [1,2]
We found seed shadows characteristic of effective seed dispersers in a degraded habitat: macaques dispersed a high number of medium- and large-seeded species both within the native forest (DEF) and toward the plantations and produced highly leptokurtic dispersal kernels indicating relatively high levels of long-distance dispersal [55,56]
The relative long dispersal distances we found were probably related to macaques’ long retention times, combined with their spread out movement patterns affected by low native fruit availability in the degraded forest fragment [32]
Summary
Anthropogenic disturbance is so prevalent that no pristine ecosystem remains across the world.Primary tropical forest loss and degradation due to agriculture, plantations and infrastructural conversions, are the driving forces of a massive tropical biodiversity crisis [1,2]. Forests 2020, 11, 1184 or the movement of seeds away from their parent plant, influences spatial structure and dynamics of plant populations, ensuring forest recruitment and regeneration and allows establishing linkages between degraded habitats [3,4,5]. Dispersal away from the parent plant reduces density-dependent and distance-dependent seed and seedling mortality, while favoring gene flow and dispersal towards a suitable site for germination and establishment [6,7,8]. Determining the seed deposition pattern of a plant population, its seed shadow [3] in degraded habitats, is crucial for providing the template for the spatial distribution of adult plants, understanding dispersal processes within particular habitats including the outcomes of the post dispersal processes [10] and predicting the evolution of forest ecosystems [11,12]
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