Frugivore Behavioural Details Matter for Seed Dispersal: A Multi-Species Model for Cantabrian Thrushes and Trees

Abstract

Animal movement and behaviour is fundamental for ecosystem functioning. The process of seed dispersal by frugivorous animals is a showcase for this paradigm since their behaviour shapes the spatial patterns of the earliest stage of plant regeneration. However, we still lack a general understanding of how intrinsic (frugivore and plant species traits) and extrinsic (landscape features) factors interact to determine how seeds of a given species are more likely to be deposited in some places more than in others. We develop a multi-species mechanistic model of seed dispersal based on frugivore behavioural responses to landscape heterogeneity. The model was fitted to data from three-years of spatially-explicit field observations on the behaviour of six frugivorous thrushes and the fruiting patterns of three fleshy-fruited trees in a secondary forest of the Cantabrian range (N Spain). With such model we explore how seed rain patterns arise from the interaction between animal behaviour and landscape heterogeneity. We show that different species of thrushes respond differently to landscape heterogeneity even though they belong to the same genus, and that provide complementary seed dispersal functions. Simulated seed rain patterns are only realistic when at least some landscape heterogeneity (forest cover and fruit abundance) is taken into account. The common and simple approach of re-sampling movement data to quantify seed dispersal produces biases in both the distance and the habitat at which seeds arrive. Movement behaviour not only affects dispersal distance and seed rain patterns but also can affect frugivore diet composition even if there is no built-in preference for fruiting species. In summary, the fate of seeds produced by a given plant species is strongly affected by both the composition of the frugivore assemblage and the landscape-scale context of the plant location, including the presence of fruits from other plants (from the same or different species).

Geographic consistency in the seed dispersal patterns of Taxus baccata L. in the Iberian Peninsula

“…Conservation and management practices should focus on maintaining a frugivore assemblage as diverse as possible to allow for complementary seed dispersal (García & Martínez, 2012;Escribano-Avila et al, 2014), thus increasing the chance for a seed to reach favourable conditions and acus preferentially forage around the focal trees, sometimes in big flocks (T. iliacus), and fly short distances towards the neighbouring microhabitats (Martínez et al, 2008), thus most likely dispersing the seeds within forest patches. On the other hand, Turdus viscivorus tends to fly long distances and hence would disperse a substantial amount of seeds among forest patches (Jordano & Schupp, 2000;Martínez et al, 2008;Morales et al, 2013). Indeed, Morales et al (2013) showed that T. merula generated a more locally aggregated seed rain than T. viscivorus, who produced a more homogeneous seed rain at the landscape scale.…”

“…On the other hand, Turdus viscivorus tends to fly long distances and hence would disperse a substantial amount of seeds among forest patches (Jordano & Schupp, 2000;Martínez et al, 2008;Morales et al, 2013). Indeed, Morales et al (2013) showed that T. merula generated a more locally aggregated seed rain than T. viscivorus, who produced a more homogeneous seed rain at the landscape scale. We observed similar patterns at our study sites.…”

“…As a group, thrushes largely select forested habitats, or trees when forest fragments are scarce, and usually avoid open habitats (Jordano & Schupp, 2000;García et al, 2010;Martínez & García, 2015a). In autumn, during the fruiting season of the fleshy-fruited species at our study sites, thrushes' behavior is principally driven by fruit resource-tracking and protection against predators (García et al, 2011;Morales et al, 2013;Martínez & García, 2015b). This spatial behavior would then explain the skewed spatial patterns of seed dispersal in yew across its Iberian distribution range.…”

Functional Equivalence in Seed Dispersal Effectiveness of Podocarpus parlatorei in Andean Fruit-Eating Bird Assemblages

“…Large body mass species usually remove larger numbers of fruits and move seeds over longer distances than small species (Nathan et al, 2008;Wotton and Kelly, 2012;Morales et al, 2013). Although fruit-eating assemblages recorded in this study were entirely composed of small-sized birds (<100 g body mass), at least three medium-to-large bird species also dispersed P. parlatorei seeds in the undisturbed forest sites.…”

Complementary Effects of Species Abundances and Ecological Neighborhood on the Occurrence of Fruit-Frugivore Interactions

“…Their main frugivores are thrushes (Martínez et al, 2008): blackbird (Turdus merula), song thrush (T. philomelos) and mistle thrush (T. viscivorus), which are resident species, and fieldfare (T. pilaris), redwing (T. iliacus), and ring-ouzel (T. torquatus), which are over-wintering species in northern Spain. Despite sharing a strong taxonomic affinity, these thrush species may differ in their response to landscape structure and habitat features (Martínez et al, 2008;Morales et al, 2013).…”