Showing papers by "Andreas Hemp published in 2018"

Phylogenetic classification of the world's tropical forests

Abstract: Knowledge about the biogeographic affinities of the world’s tropical forests helps to better understand regional differences in forest structure, diversity, composition, and dynamics. Such understanding will enable anticipation of region-specific responses to global environmental change. Modern phylogenies, in combination with broad coverage of species inventory data, now allow for global biogeographic analyses that take species evolutionary distance into account. Here we present a classification of the world’s tropical forests based on their phylogenetic similarity. We identify five principal floristic regions and their floristic relationships: (i) Indo-Pacific, (ii) Subtropical, (iii) African, (iv) American, and (v) Dry forests. Our results do not support the traditional neo- versus paleotropical forest division but instead separate the combined American and African forests from their Indo-Pacific counterparts. We also find indications for the existence of a global dry forest region, with representatives in America, Africa, Madagascar, and India. Additionally, a northern-hemisphere Subtropical forest region was identified with representatives in Asia and America, providing support for a link between Asian and American northern-hemisphere forests.

Plant and animal functional diversity drive mutualistic network assembly across an elevational gradient

Abstract: Species' functional traits set the blueprint for pair-wise interactions in ecological networks. Yet, it is unknown to what extent the functional diversity of plant and animal communities controls network assembly along environmental gradients in real-world ecosystems. Here we address this question with a unique dataset of mutualistic bird-fruit, bird-flower and insect-flower interaction networks and associated functional traits of 200 plant and 282 animal species sampled along broad climate and land-use gradients on Mt. Kilimanjaro. We show that plant functional diversity is mainly limited by precipitation, while animal functional diversity is primarily limited by temperature. Furthermore, shifts in plant and animal functional diversity along the elevational gradient control the niche breadth and partitioning of the respective other trophic level. These findings reveal that climatic constraints on the functional diversity of either plants or animals determine the relative importance of bottom-up and top-down control in plant-animal interaction networks.

Plant niche breadths along environmental gradients and their relationship to plant functional traits

Abstract: AIMS: We tested whether plant species niche breadths decrease with increasing species richness due to competition on temperature, precipitation and disturbance gradients We assumed that niche optima, niche breadth and niche volume are related to plant functional traits, indicating competitive ability and adaptation to environmental stress Finally, we wanted to identify habitats dominated by species with small niche breadths most prone to environmental change LOCATION: Southern slopes of Mount Kilimanjaro, Tanzania METHODS: We calculated species distribution models for 1,492 plant species based on the presence/absence data on 969 plots using generalized linear models We derived niche breadths, optima and volumes and investigated their relationship with plant functional traits with principal component regression to account for high trait correlations RESULTS: Niche breadths of individual species increased with elevation, precipitation and disturbance Averaged community elevation niche breadth and niche volume decreased with increasing species richness Plant functional traits explained about 40% and 50% of the variation in niche optima and breadths, respectively Size and growth traits were significant predictors of niche breadths on all gradients, whereas traits indicating reproductive strategy were not significant on the precipitation gradient MAIN CONCLUSIONS: Our results support the notion of decreasing niche breadth with increasing temperature, possibly a result of competition due to increased diversification rates and hence species richness However, the complexity of the niche breadth–species richness patterns on the other gradients shows that additional covariables shape species niche breadths apart from competition Plant species with narrow niche breadths dominated natural savannas around Mount Kilimanjaro, indicating strong sensitivity to the ongoing conversion of savanna to fields and grasslands

Broken bridges: The isolation of Kilimanjaro's ecosystem.

Abstract: Biodiversity studies of global change mainly focus on direct impacts such as losses in species numbers or ecosystem functions. In this study, we focus on the long-term effects of recent land-cover conversion and subsequent ecological isolation of Kilimanjaro on biodiversity in a paleobiogeographical context, linking our findings with the long-standing question whether colonization of African mountains mainly depended on long-distance dispersal, or whether gradual migration has been possible through habitat bridges under colder climates. For this, we used Orthoptera as bioindicators, whose patterns of endemism and habitat demands we studied on about 500 vegetation plots on Kilimanjaro and Mt. Meru (Tanzania) since 1996. Land-cover changes in the same area were revealed using a supervised classification of Landsat images from 1976 to 2000. In 1976, there was a corridor of submontane forest vegetation linking Kilimanjaro with Mt. Meru, replaced by human settlements and agriculture after 2000. Until recently, this submontane forest bridge facilitated the dispersal of forest animals, illustrated by the large number of endemic submontane forest Orthoptera shared by both mountains. Furthermore, the occurrence of common montane endemics suggests the existence of a former forest corridor with montane vegetation during much earlier times under climatic conditions 2-7°C cooler and 400-1,700 mm wetter than today. Based on the endemicity patterns of forest Orthoptera, negative consequences are predicted due to the effects of isolation, in particular for larger forest animals. Kilimanjaro is becoming an increasingly isolated ecosystem with far reaching consequences for diversity and endemism. Forest bridges between East African mountains acted as important migratory corridors and are not only a prehistoric phenomenon during periods with other climatic conditions but also disappeared in some places recently due to increasing and direct anthropogenic impact.

Seed-dispersal networks respond differently to resource effects in open and forest habitats

Abstract: While patterns in species diversity have been well studied across large‐scale environmental gradients, little is known about how species’ interaction networks change in response to abiotic and biotic factors across such gradients. Here we studied seed‐dispersal networks on 50 study plots distributed over ten different habitat types on the southern slopes of Mt Kilimanjaro, Tanzania, to disentangle the effects of climate, habitat structure, fruit diversity and fruit availability on different measures of interaction diversity. We used direct observations to record the interactions of frugivorous birds and mammals with fleshy‐fruited plants and recorded climatic conditions, habitat structure, fruit diversity and availability. We found that Shannon interaction diversity (H) increased with fruit diversity and availability, whereas interaction evenness (EH) and network specialization (H₂) responded differently to changes in fruit availability depending on habitat structure. The direction of the effects of fruit availability on EH and H₂ differed between open habitats at the mountain base and structurally complex habitats in the forest belt. Our findings illustrate that interaction networks react differently to changes in environmental conditions in different ecosystems. Hence, our findings demonstrate that future projections of network structure and associated ecosystem functions need to account for habitat differences among ecosystems.

Late Quaternary ecotone change between sub‐alpine and montane forest zone on the leeward northern slope of Mt. Kilimanjaro

Abstract: Tropical montane forests are crucial for providing many services for fastgrowing local human populations (Gradstein, Homeier, & Gansert, 2008). Among the essential resources provided by tropical montane forests, fresh water is one of the most important. In particular, air masses at elevation generate fog and strong orographic precipitation contributing 50% to −90% of total water discharges for the lowlands in tropical semiarid regions (Viviroli & Weingartner, 2004). Such conditions are typical for East African mountains such Received: 9 November 2017 | Accepted: 1 April 2018 DOI: 10.1111/jvs.12639

Elevational transplantation suggests different responses of African submontane and savanna plants to climate warming

Abstract: Summary 1.Despite strong climate change in the tropics, little is known about the responses of tropical plants to changing environments. Moreover, while variation in responses to climate change across plant functional groups may help to predict future vegetation dynamics, tropical multi-species studies are missing. 2.To study plant responses to changes in temperature, we compared the survival, growth and reproduction of 101 herbaceous species originating from the savanna and the submontane vegetation zones in two experimental gardens representing the climate of both zones at Kilimanjaro, Tanzania. Additionally, we tested whether plant functional groups, such as annuals and perennials, shade-tolerant and shade-intolerant species, grasses and forbs, and natives and exotics differ in their responses to transplantation. 3.We show that the submontane species in the lower Kilimanjaro area clearly prefer the cooler submontane temperature in terms of survival, growth and reproduction, while savanna plants can grow equally well under both, the submontane and the savanna temperature regimes. This suggests that tropical submontane plants will likely face severe challenges with future climate warming and that the upper distributional limit of savanna plants may be due to biotic interactions rather than to climate. Moreover, we found different responses of grasses and forbs, and natives and exotics to transplantation irrespective of their origin, underlining the importance of considering plant functional groups in climate change research. 4.Synthesis: We demonstrate different responses of tropical submontane and savanna plants to experimental temperature variation. Together with the observed differences between important functional plant groups, this leads us to suggest that strong future changes in vegetation composition on African tropical mountains are likely. This article is protected by copyright. All rights reserved.

Asplenium arcumontanum (Aspleniaceae), a new species from the Eastern Arc Mountains of Tanzania

Abstract: Asplenium arcumontanum (Aspleniaceae), a new terrestrial forest species from northern Tanzania, is described and illustrated. This taxon is closely related to the more widespread A. elliottii, a vicariant species with similar habitat requirements but a near-allopatric distribution. Asplenium arcumontanum fits the typical altitudinal zonation pattern of equatorial African gemmiferous ferns, and the endemism pattern of the Eastern Arc Mountains. Its restricted distribution further underscores the urgent need to conserve residual forest patches in this distinctive range.

Conservation Status of the Elegant Yellow-Black Bush-Cricket Meruterrana elegans (Orthoptera: Phaneropterinae)—A Critically Endangered Species on Mount Kenya

Abstract: Two populations of Meruterrana elegans, a monotypic bush-cricket genus, endemic to Mount Kenya in Kenya were surveyed. The species is restricted to Cassipourea forest, a forest community vanishing rapidly on Mount Kenya and with it Meruterrana elegans, which therefore should be included to the IUCN red list of threatened species as Critically Endangered.