Trait matching and sampling effort shape the structure of the frugivory network in Afrotropical forests

Frugivory in tropical forests is a major ecological process as most tree species rely on frugivores to disperse their seeds. However, the underlying mechanisms driving frugivore-plant networks remain understudied. Here, we evaluate the data available on the Afrotropical frugivory network to identify structural properties, as well as assess knowledge gaps. We assembled a database of frugivory interactions from the literature with > 10 000 links, between 807 tree and 285 frugivore species. We analysed the network structure using a block model that groups species with similar interaction patterns and estimates interaction probabilities among them. We investigated the species traits related to this grouping structure. This frugivory network was simplified into 14 tree and 14 frugivore blocks. The block structure depended on the sampling effort among species: Large mammals were better-studied, while smaller frugivores were the least studied. Species traits related to frugivory were strong predictors of the species composition of blocks and interactions among them. Fruits from larger trees were consumed by most frugivores, and large frugivores had higher probabilities to consume larger fruits. To conclude, this large-scale frugivory network was mainly structured by species traits involved in frugivory, and as expected by the distribution areas of species, while still being limited by sampling incompleteness.

Seedling recruitment under isolated trees in a tea plantation provides a template for forest restoration in eastern Africa

Natural regeneration is less expensive than tree planting, but determining what species will arrive and establish to serve as templates for tropical forest restoration remains poorly investigated in eastern Africa. This study summarises seedling recruitment under 29 isolated legacy trees (14 trees comprised of three exotic species and 15 trees comprised of seven native species) in tea plantations in the East Usambara Mountains, Tanzania. Among the findings were that pioneer recruits were very abundant whereas non-pioneers were disproportionately fewer. Importantly, 98% of all recruits were animal-dispersed. The size of legacy trees, driven mostly by the exotic Grevillea robusta, and to some extent, the native Milicia excelsa, explained abundance of recruits. The distribution of bird-dispersed recruits suggested that some bird species use all types of legacy trees equally in this fragmented landscape. In contrast, the distribution of bat-dispersed recruits provided strong evidence that seedling composition differed under native versus exotic legacy trees likely due to fruit bats showing more preference for native legacy trees. Native, as compared to exotic legacy trees, had almost two times more non-pioneer recruits, with Ficus and Milicia excelsa driving this trend. Implications of our findings regarding restoration in the tropics are numerous for the movement of native animal-dispersed tree species in fragmented and disturbed tropical forests surrounded by farmland. Isolated native trees that bear fleshy fruits can attract more frugivores, resulting not only in high recruitment under them, but depending on the dispersal mode of the legacy trees, also different suites of recruited species. When selecting tree species for plantings, to maximize visitation by different dispersal agents and to enhance seedling recruit diversity, bat-dispersed Milicia excelsa and Ficus species are recommended.

Investigating the direct and indirect effects of forest fragmentation on plant functional diversity

Ongoing habitat loss and fragmentation alter the functional diversity of forests. Generalising the magnitude of change in functional diversity of fragmented landscapes and its drivers is challenging because of the multiple scales at which landscape fragmentation takes place. Here we propose a multi-scale approach to determine whether fragmentation processes at the local and landscape scales are reducing functional diversity of trees in the East Usambara Mountains, Tanzania. We employ a structural equation modelling approach using five key plant traits (seed length, dispersal mode, shade tolerance, maximum tree height, and wood density) to better understand the functional responses of trees to fragmentation at multiple scales. Our results suggest both direct and indirect effects of forest fragmentation on tree functional richness, evenness and divergence. A reduction in fragment area appears to exacerbate the negative effects resulting from an increased amount of edge habitat and loss of shape complexity, further reducing richness and evenness of traits related to resource acquisition and favouring tree species with fast growth. As anthropogenic disturbances affect forests around the world, we advocate to include the direct and indirect effects of forest fragmentation processes to gain a better understanding of shifts in functional diversity that can inform future management efforts.

The effects of habitat loss and fragmentation on plant functional traits and functional diversity: what do we know so far?

Habitat loss and fragmentation result in significant landscape changes that ultimately affect plant diversity and add uncertainty to how natural areas will respond to future global change. This uncertainty is important given that the loss of biodiversity often includes losing key ecosystem functions. Few studies have explored the effects of landscape changes on plant functional diversity and evidence so far has shown far more pervasive effects than previously reported by species richness and composition studies. Here we present a review on the impact of habitat loss and fragmentation on (1) individual functional traits-related to persistence, dispersal and establishment-and (2) functional diversity. We also discuss current knowledge gaps and propose ways forward. From the literature review we found that studies have largely focused on dispersal traits, strongly impacted by habitat loss and fragmentation, while traits related to persistence were the least studied. Furthermore, most studies did not distinguish habitat loss from spatial fragmentation and were conducted at the plot or fragment-level, which taken together limits the ability to generalize the scale-dependency of landscape changes on plant functional diversity. For future work, we recommend (1) clearly distinguishing the effects of habitat loss from those of fragmentation, and (2) recognizing the scale-dependency of predicted responses when functional diversity varies in time and space. We conclude that a clear understanding of the effects of habitat loss and fragmentation on functional diversity will improve predictions of the resiliency and resistance of plant communities to varying scales of disturbance.

Isolation and development of microsatellite loci in an African Woodpecker (Campethera nivosa) using polymerase chain reaction and DNA sequencing

BACKGROUND

The Buff-spotted Woodpecker (Campethera nivosa) is a resident bird species that is distributed in lowland rainforest habitats from western to eastern Africa. We developed species-specific microsatellite markers to examine the population genetics of this species.

FINDINGS

Twenty-one microsatellite loci were isolated from C. nivosa. Of these, 15 were found to amplify consistently. These loci were then tested for variability in 15 individuals from different lowland forest localities. The number of alleles ranged from 3 to 13 per locus, with observed and expected heterozygosity ranging from 0.100 to 0.917 and 0.485 to 0.901, respectively. Four loci exhibited significant heterozygote deficiency while one had an excess of heterozygotes. None of the loci exhibited linkage disequilibrium.

CONCLUSION

These polymorphic microsatellite markers will be used to study genetic variability in populations of C. nivosa across either sides of the Congo River to evaluate the effect of the river as a barrier to gene flow.

Disperser limitation and recruitment of an endemic African tree in a fragmented landscape

Forest fragmentation may have positive or negative effects on tropical tree populations. Our earlier study of an endemic African tree, Leptonychia usambarensis (Sterculiaceae), in the East Usambara Mountains of Tanzania, found poorer recruitment of seedlings and juveniles in small fragments compared to continuous forest, and concomitant reduction of seed-dispersal agents and seed dispersal. However, the possibility that other biotic or abiotic consequences of the fragmentation process contribute to diminished recruitment in fragments was left open. Here we test whether excessive seed predation, diminished fecundity, low seed quality, or adverse abiotic effects acted independently or in concert with reduced seed dispersal to limit seedling and juvenile recruitment in fragments. Extended observations of disperser activity, a seed placement experiment, seed predator censuses, and reciprocal seedling transplants from forest and fragment sources failed to support the alternative hypotheses for poorer seedling and juvenile recruitment in fragments, leaving reduced seed dispersal as the most plausible mechanism. Poorer recruitment of this species in forest fragments, where high edge-to-area ratios admit more light than in continuous forest, is particularly striking because the tree is an early successional species that might be expected to thrive in disturbed microhabitats.

Microsatellite loci for two East African tree species, Leptonychia usambarensis (Sterculiaceae) and Sorindeia madagascariensis (Anacardiaceae)

We isolated 20 trinucleotide microsatellites from two African tree species: Sorindeia madagascariensis (nine microsatellites) and Leptonychia usambarensis (11 microsatellites). Number of alleles ranged from three to seven in Sorindeia and two to 10 in Leptonychia. Observed heterozygosity ranged from 0.025 to 0.829 for Sorindeia and from 0.226 to 0.933 for Leptonychia. Two loci from each species departed from Hardy-Weinberg equilibrium. These microsatellite markers will be used to study how forest fragmentation affects pollination and seed dispersal processes of these tree species.

Forest fragmentation severs mutualism between seed dispersers and an endemic African tree

Because bird species are lost when forests are fragmented into small parcels, trees that depend on fruit-eating birds for seed dispersal may fail to recruit seedlings if dispersal agents disappear. We tested this prediction in rainforest in the East Usambara Mountains of Tanzania, by using the endemic tree Leptonychia usambarensis (Sterculiaceae) and birds that disperse its seeds. We investigated bird abundance and Leptonychia dispersal ecology in fragments isolated for >70 yr, as compared with 3,500 ha of continuous forest. Birds that dispersed Leptonychia seeds in continuous forest were rare or absent in small fragments, where fewer seeds were removed from each tree, far fewer seedlings occurred >10 m from parent trees, and far more seedlings occurred in dense aggregations under parental crowns. Overall, our samples showed that fewer juvenile Leptonychia recruited in fragments than in continuous forest. We provide solid evidence that deficient dispersal due to habitat fragmentation seriously impacts the reproductive cycle of a tropical bird-dispersed tree.

Comparative analysis of glycosylated and nonglycosylated filarial homologues of the 20-kilodalton retinol binding protein from Onchocerca volvulus (Ov20)

Ov20 is a structurally novel 20-kDa retinol binding protein secreted by Onchocerca volvulus. Immunological and biological investigation of this protein has been hampered by the inability to maintain O. volvulus in a laboratory setting. In an effort to find a system more amenable to laboratory investigation, we have cloned, sequenced, and expressed cDNA encoding homologues of Ov20 from two closely related filarial species, Brugia malayi (Bm20) and Acanthocheilonema viteae (Av20). Sequence comparisons have highlighted differences in glycosylation of the homologues. We present here an analysis of mouse immune responses to Ov20, Bm20, and Av20. The results suggest a strong genetic restriction in response to native Bm20 that is overcome when recombinant, nonnative material is used. Reactivity of human filarial sera to the three recombinant proteins confirmed previous specificity studies with Ov20 but highlighted important differences in the reactivity patterns of the O. volvulus and B. malayi homologues that may be due to differences in glycosylation patterns. Ov20 is a dominant antigen in infected individuals, while Bm20 is not. The availability of the B. malayi homologue enabled us to use defined murine reagents and inbred strains for genetic analysis of responsiveness in a way that is not possible for Ov20. However, the close sequence similarity between Ov20 and Av20 suggests that the A. viteae model may be more suited to the investigation of the biological functions of Ov20.