Showing papers by "Holger Kreft published in 2015"

Global exchange and accumulation of non-native plants

Abstract: All around the globe, humans have greatly altered the abiotic and biotic environment with ever-increasing speed. One defining feature of the Anthropocene epoch is the erosion of biogeographical barriers by human-mediated dispersal of species into new regions, where they can naturalize and cause ecological, economic and social damage. So far, no comprehensive analysis of the global accumulation and exchange of alien plant species between continents has been performed, primarily because of a lack of data. Here we bridge this knowledge gap by using a unique global database on the occurrences of naturalized alien plant species in 481 mainland and 362 island regions. In total, 13,168 plant species, corresponding to 3.9% of the extant global vascular flora, or approximately the size of the native European flora, have become naturalized somewhere on the globe as a result of human activity. North America has accumulated the largest number of naturalized species, whereas the Pacific Islands show the fastest increase in species numbers with respect to their land area. Continents in the Northern Hemisphere have been the major donors of naturalized alien species to all other continents. Our results quantify for the first time the extent of plant naturalizations worldwide, and illustrate the urgent need for globally integrated efforts to control, manage and understand the spread of alien species.

Global priorities for an effective information basis of biodiversity distributions.

Abstract: Severe gaps and biases in digital accessible information (DAI) of species distributions hamper prospects of safeguarding biodiversity and ecosystem services and reliably addressing central questions in ecology and evolution. Accordingly, governments have agreed on improving and sharing biodiversity knowledge by 2020 (United Nations Convention on Biological Diversity’s Aichi target 19). To achieve this target, gaps in DAI must be identified, and actions prioritized to address their root causes. We take terrestrial vertebrates, an iconic and comparatively well-studied group, as a model and present the first globally comprehensive assessment of patterns and drivers of gaps in DAI, based on an integration of 157 million validated point records with 21,170 expert-based distribution maps. We demonstrate that outside a few well-sampled regions, DAI provides a very limited and spatially highly biased inventory of actual biodiversity. Coarser spatial grains result in more complete inventories, but provide insufficient detail for conservation and resource management. Surprisingly, large emerging economies are particularly under-represented in global DAI, even more so than species-rich, developing countries in the tropics. Multi-model inference reveals that completeness is mainly limited by distance to researchers, locally available research funding, and political participation in data-sharing networks, rather than transportation infrastructure, or size and funding of Western data contributors as often assumed. Our study provides an empirical baseline to advance strategies of enhancing the global information basis of biodiversity. In particular, our results highlight the need for targeted data integration from non-Western data holders and intensified cooperation to more effectively address societal biodiversity information needs.

Terminology and quantification of environmental heterogeneity in species-richness research.

Abstract: Spatial environmental heterogeneity (EH) is an important driver of species diversity, and its influence on species richness has been analysed for numerous taxa, in diverse ecological settings, and over a large range of spatial scales. The variety and ambiguity of concepts and terminology, however, have hampered comparisons among studies. Based on a systematic literature survey of 192 studies including 1148 data points, we provide an overview of terms and measures related to EH, and the mechanisms that relate EH to species richness of plants and animals in terrestrial systems. We identify 165 different measures used to quantify EH, referred to by more than 350 measure names. We classify these measures according to their calculation method and subject area, finding that most studies have analysed heterogeneity in land cover, topography, and vegetation, whereas comparatively few studies have focused on climatic or soil EH. Overall, elevation range emerged as the most frequent measure in our dataset. We find that there is no consensus in the literature about terms (such as ‘habitat diversity’ or ‘habitat complexity’), their meanings and associated quantification methods. More than 100 different terms have been used to denote EH, with largely imprecise delimitations. We reveal trends in use of terms and quantification with respect to spatial scales, study taxa, and locations. Finally, we discuss mechanisms involved in EH–richness relationships, differentiating between effects on species coexistence, persistence, and diversification. This review aims at guiding researchers in their selection of heterogeneity measures. At the same time, it shows the need for precise terminology and avoidance of ambiguous synonyms to enhance understanding and foster among-study comparisons and synthesis.

Global patterns and drivers of phylogenetic structure in island floras.

Abstract: Islands are ideal for investigating processes that shape species assemblages because they are isolated and have discrete boundaries. Quantifying phylogenetic assemblage structure allows inferences about these processes, in particular dispersal, environmental filtering and in-situ speciation. Here, we link phylogenetic assemblage structure to island characteristics across 393 islands worldwide and 37,041 vascular plant species (representing angiosperms overall, palms and ferns). Physical and bioclimatic factors, especially those impeding colonization and promoting speciation, explained more variation in phylogenetic structure of angiosperms overall (49%) and palms (52%) than of ferns (18%). The relationships showed different or contrasting trends among these major plant groups, consistent with their dispersal- and speciation-related traits and climatic adaptations. Phylogenetic diversity was negatively related to isolation for palms, but unexpectedly it was positively related to isolation for angiosperms overall. This indicates strong dispersal filtering for the predominantly large-seeded, animal-dispersed palm family whereas colonization from biogeographically distinct source pools on remote islands likely drives the phylogenetic structure of angiosperm floras. We show that signatures of dispersal limitation, environmental filtering and in-situ speciation differ markedly among taxonomic groups on islands, which sheds light on the origin of insular plant diversity.

Global patterns of agricultural land-use intensity and vertebrate diversity

Abstract: Aim Land-use change is the single biggest cause of biodiversity loss. With a rising demand for resources, understanding how and where agriculture threatens biodiversity is of increasing importance. Agricultural expansion has received much attention, but where high agricultural land-use intensity (LUI) threatens biodiversity remains unclear. We address this knowledge gap with two main research questions: (1) Where do global patterns of LUI coincide with the spatial distribution of biodiversity? (2) Where are regions of potential conflict between different aspects of high LUI and high biodiversity? Location Global. Methods We overlaid thirteen LUI metrics with endemism richness, a range size-weighted species richness indicator, for mammals, birds and amphibians. We then used local indicators of spatial association to delineate statistically significant (P < 0.05) areas of high and low LUI associated with biodiversity. Results Patterns of LUI are heterogeneously distributed in areas of high endemism richness, thus discouraging the use of a single metric to represent LUI. Many regions where high LUI and high endemism richness coincide, for example in South America, China and Eastern Africa, are not within currently recognized biodiversity hotspots. Regions of currently low LUI and high endemism richness, found in many parts of Mesoamerica, Eastern Africa and Southeast Asia, may be at risk as intensification accelerates. Main conclusions We provide a global view of the geographic patterns of LUI and its concordance with endemism richness, shedding light on regions where highly intensive agriculture and unique biodiversity coincide. Past assessments of land-use impacts on biodiversity have either disregarded LUI or included a single metric to measure it. This study demonstrates that such omission can substantially underestimate biodiversity threat. A wider spectrum of relevant LUI metrics needs to be considered when balancing agricultural production and biodiversity.

Differential effects of environmental heterogeneity on global mammal species richness

Abstract: Spatial environmental heterogeneity (EH) is an important driver of species richness, affecting species coexistence, persistence and diversification. EH has been widely studied in ecology and evolution and quantified in many different ways, with a strong bias towards a few common measures of EH like elevation range. Here, we calculate 51 measures of EH within grid cells world-wide across three spatial grains to investigate similarities and differences among these measures. Moreover, we compare the association between species richness of terrestrial mammals and each EH measure to assess the impact of methodological choices on EH–richness relationships found by standard macroecological modelling approaches.

Branchfall as a demographic filter for epiphyte communities: Lessons from forest floor-based sampling

Abstract: Local variation in the abundance and richness of vascular epiphytes is often attributed to environmental characteristics such as substrate and microclimate. Less is known, however, about the impacts of tree and branch turnover on epiphyte communities. To address this issue, we surveyed branches and epiphytes found on the forest floor in 96 transects in two forests (Atlantic rainforest in Brazil and Caribbean rainforest in Panama). In the Brazilian forest, we additionally distinguished between edge and core study sites. We quantified branch abundance, epiphyte abundance, richness and proportion of adults to investigate the trends of these variables over branch diameter. Branches 90% of all branches on the forest floor. Abundance and richness of fallen epiphytes per transect were highest in the Brazilian core transects and lowest in the Panamanian transects. The majority of epiphytes on the floor (c. 65%) were found attached to branches. At all three study sites, branch abundance and branch diameter were negatively correlated, whereas epiphyte abundance and richness per branch, as well as the proportion of adults were positively correlated with branch diameter. The relationship between branch diameter and absolute epiphyte abundance or richness differed between study sites, which might be explained by differences in forest structure and dynamics. In the Panamanian forest, epiphytes had been previously inventoried, allowing an evaluation of our surveying method by comparing canopy and forest floor samplings. Individuals found on the forest floor corresponded to 13% of all individuals on branches <10 cm in diameter (including crowns), with abundance, richness and composition trends on forest floor reflecting canopy trends. We argue that forest floor surveys provide useful floristic and, most notably, demographic information particularly on epiphytes occurring on the thinnest branches, which are least accessible. Here, branchfall acts as an important demographic filter structuring epiphyte communities.

Island floras are not necessarily more species poor than continental ones

Abstract: Oceanic islands typically exhibit a lower number of species per unit area than continents owing to their geographical isolation (MacArthur & Wilson, 1967). This relationship demonstrates a remarkable consistency across spatial and taxonomic scales (MacArthur & Wilson, 1967) and has significant evolutionary consequences because island organisms are expected to respond to the empty niche space through a series of major transformations in their life-history traits (see Whittaker & Fern andez-Palacios, 2007). The biological, ecological and physiological changes are known as island syndromes, with the loss of dispersal power, changes in body size and the development of woodiness in herbaceous plant lineages being some of the most striking examples (Whittaker & Fern andezPalacios, 2007). In their seminal book, MacArthur & Wilson (1967) observed that the degree of impoverishment in bird faunas distributed across the archipelagos of Melanesia, Micronesia and Polynesia increased from islands near to New Guinea to intermediate and far islands (distance of > 3200 km from the mainland). This implies that the mismatch between species richness per unit area on continents and on islands increases with the degree of isolation of the latter, as species are progressively filtered out depending on their long-distance dispersal capacities (Whittaker & Fern andez-Palacios, 2007). However, there is mounting evidence for the existence of lineage-specific species–area relationships associated with long-distance dispersal capacities (Triantis et al., 2012; Pati~ no et al., 2014b) and this raises the question of whether communities of highly mobile organisms are necessarily less species rich on islands than on continents and, hence, whether they exhibit typical island syndromes. Here, data from a global survey of 421 land plant floras (Pati~ no et al., 2014b) were submitted to linear mixed-effects models to analyse variation in log(species richness) depending on log(area) while controlling for variation in the factors geology (continents, oceanic islands and continental islands), plant group (seed plants, ferns and fern allies, liverworts and mosses), biome and realm (the latter two as defined by Olson et al., 2001). The analyses demonstrate that whereas species richness patterns of seed plants conform to the expectations of the island impoverishment theory, spore-producing plants do not (Fig. 1). The species–area models obtained indicate that seed plants exhibit, on average, a continual decrease in species richness per unit area from continents to continental islands to oceanic islands (Fig. 1). Mosses only partially follow such a pattern, with oceanic islands showing the lowest species richness, but with continental regions and continental islands showing similar values for comparable units of area. In liverworts and ferns, the pattern is different. Whereas islands with a small area and presumably limited ecological complexity show impoverished floras, intermediate and large sized oceanic and continental islands display similar or even slightly higher levels of species richness than continents. Thus, oceanic island floras of liverworts and ferns with a log(area) ranging from three to four units (10– 10 km), and continental island floras with a log(area) from five to six (10– 10 km), exhibit higher species richness compared to continents, a pattern at odds with expectations (Fig. 1). Possible explanations for the patterns observed in spore-producing land plants are: (1) higher speciation rates on islands than on continents; (2) lower extinction rates on islands; (3) higher dispersal power than in seed plants; or (4) a higher carrying capacity on large islands per unit area than on continents. The generally very low rates of endemism in oceanic island ferns and bryophytes (Pati~ no et al., 2014a) suggest a lack of extensive island radiations in these groups, thus pointing to the other hypotheses. A global comparison of island and mainland environments revealed that wet climates typical of tropical and, especially, temperate rain forest biomes are over-represented on islands, whereas hot and dry desert climates are under-represented (Weigelt et al., 2013). These general features of islands are particularly suitable for organisms such as bryophytes and ferns that rely greatly on environmental humidity for water uptake (e.g. poikilohydry in filmy ferns and bryophytes) and exhibit lower temperature optima than flowering plants (Vanderpoorten & Goffinet, 2009; Mehltreter et al., 2010). Given the ecological requirements of these spore-producing plant groups with higher dispersal capabilities than in seed plants, such a combination of humidity and mild temperatures on islands could lead to a reduced extinction risk following colonization and a potentially higher carrying capacity than in continental regions of similar area. The fact that island spore-producing floras are not impoverished suggests that the shifts in the expression of reproductive traits observed in island bryophytes, such as the higher investment in asexual reproduction as well as the higher frequency of fertile shoots (Pati~ no et al., 2013), do not represent a response to empty niche space, as island biogeography theory predicts. Rather, such changes may reflect a response to the specific climate conditions that prevail on islands. Such environmental conditions may also be found on continents, but proportionally represent a smaller fraction of continental climates (Weigelt et al., 2013) and, hence, the emergence of a bias in life-history traits associated with such climates would not be linked to geographical isolation either. In seed plants, experimental support for the loss of dispersal capacity on islands is equivocal (contrast, e.g. Whittaker & Fern andez-Palacios, 2007 and Talavera et al., 2012) and in sporeproducing plants, a study on the dispersal capacity of the moss Rhynchostegium riparioides failed to demonstrate any significant difference in migration rates in insular and continental populations (Hutsem ekers et al., 2011). This raises the question of whether other typical island syndromes,

Ecosystem functions of oil palm plantations - a review

Abstract: Oil palm plantations have expanded rapidly in the last decades. This large-scale land-use change has had great impacts on both the areas converted to oil palm and their surroundings. Howev-er, research on the impacts of oil palm agriculture is scattered and patchy, and no clear overview ex-ists. Here, we address this gap through a systematic and comprehensive literature review of all ecosys-tem functions in oil palm plantations. We compare ecosystem functions in oil palm plantations to those in forests as forests are often cleared for the establishment of oil palm. We find that oil palm planta-tions generally have reduced ecosystem functioning compared to forests. Some of these functions are lost globally, such as those to gas and climate regulation and to habitat and nursery functions. The most serious impacts occur when land is cleared to establish new plantations, and immediately after-wards, especially on peat soils. To variable degrees, plantation management can prevent or reduce losses of some ecosystem functions. The only ecosystem function which increased in oil palm planta-tions is, unsurprisingly, the production of marketable goods. Our review highlights numerous research gaps. In particular, there are significant gaps with respect to information functions (socio-cultural functions). There is a need for empirical data on the importance of spatial and temporal scales, such as the differences between plantations in different environments, of different sizes, and of different ages. Finally, more research is needed on developing management practices that can off-set the losses of ecosystem functions.

Global drivers of species variation in mobilized point-occurrence information

Abstract: Despite the central role of species distributions in ecology and conservation, occurrence information remains geographically and taxonomically incomplete and biased. Numerous socio-economic and ecological drivers of uneven record collection and mobilization among species have been suggested, but the generality of their effects remains untested. We develop scale-independent metrics of range coverage and geographical record bias, and apply them to 2.8M point-occurrence records of 3,625 mammal species to evaluate 13 putative drivers of species-level variation in data availability. We find that data limitations are mainly linked to range size and shape, and the geography of socioeconomic conditions. Surprisingly, species attributes related to detection and collection probabilities, such as body size or diurnality, are much weaker predictors of the amount and range coverage of available records. Our results highlight the need to prioritize range-restricted species and to address the key socio-economic drivers of data bias in data mobilization efforts and distribution modeling.

RESEARCH Global patterns of agricultural land-use intensity and vertebrate diversity

Abstract: Aim Land-use change is the single biggest cause of biodiversity loss. With a rising demand for resources, understanding how and where agriculture threatens biodiversity is of increasing importance. Agricultural expansion has received much attention, but where high agricultural land-use intensity (LUI) threatens biodiversity remains unclear. We address this knowledge gap with two main research questions: (1) Where do global patterns of LUI coincide with the spatial distribution of biodiversity? (2) Where are regions of potential conflict between different aspects of high LUI and high biodiversity? Location Global. Methods We overlaid thirteen LUI metrics with endemism richness, a range size-weighted species richness indicator, for mammals, birds and amphibians. We then used local indicators of spatial association to delineate statistically significant (P < 0.05) areas of high and low LUI associated with biodiversity. Results Patterns of LUI are heterogeneously distributed in areas of high endemism richness, thus discouraging the use of a single metric to represent LUI. Many regions where high LUI and high endemism richness coincide, for example in South America, China and Eastern Africa, are not within currently recognized biodiversity hotspots. Regions of currently low LUI and high endemism richness, found in many parts of Mesoamerica, Eastern Africa and Southeast Asia, may be at risk as intensification accelerates. Main conclusions We provide a global view of the geographic patterns of LUI and its concordance with endemism richness, shedding light on regions where highly intensive agriculture and unique biodiversity coincide. Past assessments of land-use impacts on biodiversity have either disregarded LUI or included a single metric to measure it. This study demonstrates that such omission can substantially underestimate biodiversity threat. A wider spectrum of relevant LUI metrics needs to be considered when balancing agricultural production and biodiversity.