Browse
Recent Submissions
Now showing 1 - 5 of 52
- ItemHow competitive intransitivity and niche overlap affect spatial coexistence(2021) Yang, Y.Q.; Hui, C.Competitive intransitivity is mostly considered outside the main body of coexistence theories that rely primarily on the role of niche overlap and differentiation. How the interplay of competitive intransitivity and niche overlap jointly affects species coexistence has received little attention. Here, we consider a rock‐paper‐scissors competition system where interactions between species can represent the full spectra of transitive‐intransitive continuum and niche overlap/differentiation under different levels of competition asymmetry. By comparing results from pair approximation that only considers interference competition between neighbouring cells in spatial lattices, with those under the mean‐field assumption, we show that (1) species coexistence under transitive competition is only possible at high niche differentiation; (2) in communities with partial or pure intransitive interactions, high levels of niche overlap are not necessary to beget species extinction; and (3) strong spatial clustering can widen the condition for intransitive loops to facilitate species coexistence. The two mechanisms, competitive intransitivity and niche differentiation, can support species persistence and coexistence, either separately or in combination. Finally, the contribution of intransitive loops to species coexistence can be enhanced by strong local spatial correlations, modulated and maximised by moderate competition asymmetry. Our study, therefore, provides a bridge to link intransitive competition to other generic ecological theories of species coexistence.
- ItemRecent deforestation drove the spike in Amazonian fires(2020) Cardil, A.; de-Miguel, S.; Silva, C.A.; Reich, P.B.; Calkin, D.; Brancalion, P.H.S.; Vibrans, A.C.; Gamarra, J.G.P.; Zhou, M.; Pijanowski, B.C.; Hui, C.; Crowther, T.W.; Hérault, B.; Piotto, D.; Salas-Eljatib, C.; North Broadbent, E.; Almeyda Zambrano, A.M.; Picard, N.; Aragão, L.E.O.C.; Bastin, J.-F.; Routh, D.; van den Hoogen, J.; Peri, P.L.; Liang, J.
- ItemExtending biodiversity conservation with functional and evolutionary diversity: a case study of South African sparid fishes(2020) Henriques, R.; Mann, B.Q.; Nielsen, E.S.; Hui, C.; van der Heyden, S.Designing marine protected area (MPA) networks has relied primarily on species- or habitat-based measures that assess spatial distributions of biodiversity. Molecular and functional data have the potential to unlock information regarding the evolutionary uniqueness and resilience of natural communities, making phylogenetic diversity (PD) and functional diversity (FD) effective tools for spatial planning. These are, however, rarely used in marine conservation planning. In South Africa, MPAs have been implemented to protect rare and valuable fishery resources, such as members of the Sparidae (seabreams), but have not considered different dimensions of biodiversity, such as its phylogenetic and functional components. Here, we mapped species distributions, phylogenetic relationships and functional features of the Sparidae in South Africa to refine how biodiversity is spatially structured for this species-rich taxonomic group. Our results show strong spatial similarities between PD and FD, suggesting that, for this group, PD is an effective surrogate for functional data. However, there was a mismatch between areas selected with different biodiversity metrics (particularly endemicity levels) and established MPAs, highlighting the need for integrated approaches to conserve this unique marine fauna.
- ItemHow geographic productivity patterns affect food-web evolution(2020) Wickman, J.; Dieckmann, U.; Hui, C.; Brannstrom, A.It is well recognized that spatial heterogeneity and overall productivity have important consequences for the diversity and community structure of food webs. Yet, few, if any, studies have considered the effects of heterogeneous spatial distributions of primary production. Here, we theoretically investigate how the variance and autocorrelation length of primary production affect properties of evolved food webs consisting of one autotroph and several heterotrophs. We report the following findings. (1) Diversity increases with landscape variance and is unimodal in autocorrelation length. (2) Trophic level increases with landscape variance and is unimodal in autocorrelation length. (3) The extent to which the spatial distribution of heterotrophs differ from that of the autotroph increases with landscape variance and decreases with autocorrelation length. (4) Components of initial disruptive selection experienced by the ancestral heterotroph predict properties of the final evolved communities. Prior to our study reported here, several authors had hypothesized that diversity increases with the landscape variance of productivity. Our results support their hypothesis and contribute new facets by providing quantitative predictions that also account for autocorrelation length and additional properties of the evolved communities.
- ItemVariation in individual biomass decreases faster than mean biomass with increasing density of bamboo stands(2020) Liu, G.H.; Hui, C.; Chen, M.; Pile, L.S.; Wang, G.G.; Wang, F.S.; Shi, P.J.The total biomass of a stand is an indicator of stand productivity and is closely related to the density of plants. According to the self-thinning law, mean individual biomass follows a negative power law with plant density. If the variance of individual biomass is constant, we can expect increased stand productivity with increasing plant density. However, Taylor's power law (TPL) that relates the variance and the mean of many biological measures (e.g. bilateral areal differences of a leaf, plant biomass at different times, developmental rates at different temperatures, population densities on different spatial or temporal scales), affects the estimate of stand productivity when it is defined as the total biomass of large plants in a stand. Because the variance of individual biomass decreases faster than mean individual biomass, differences in individual biomass decline with increasing density, leading to more homogeneous timbers of greater economic value. We tested whether TPL in plant biomass holds for different species and whether the variance of individual biomass changes faster than the mean with increasing stand density. The height, ground diameter and fresh weight of 50 bamboo species were measured in 50 stands ranging from 1 m by 1 m to 30 m by 30 m to ensure more than 150 bamboos in every stand. We separately examined TPL in height, ground diameter, and weight, and found that TPL holds for all three biological measures, with the relationship strongest for weight. Using analysis of covariance to compare the regression slopes of logarithmic mean and variance against the logarithm of density, we found that the variance in individual biomass declined faster than the mean with increasing density. This suggests that dense planting reduced mean individual biomass but homogenized individual biomass. Thus, there exists a trade-off between effective stand productivity and stand density for optimal forest management. Sparse planting leads to large variation in individual biomass, whereas dense planting reduces mean individual biomass. Consequently, stand density for a plantation should be set based on this trade-off with reference to market demands.