Macroecology

Macroecology

Which factors govern large-scale patterns of species richness? This is one of the central questions in a relativley young discipline called macroecology. Although, at first sight the question seem to be rather simple numerous hypotheses on the origin and maintenance of gradients in species richness have been proposed during the last decades. Working mainly with plant richness data sets we want to answer the following questions:

• Which factors determine the unequal distribution of species richness?

• Which processes are responsible?

• How is the influence of other biological and ecological traits like, eg., range size, taxonomic idiosyncracies, ecological strategies?

• How might biological diversity change and interact in the context of the global environmental change?

Mutke, J.,Sommer, J.H., Kreft, H., Kier, G. & W. Barthlott (2011): Vascular plant diversity in a changing world: global centres and biome-specific patterns. In: Habel, J. C. & F. Zachos (eds.): Biodiversity Hotspots – Evolution and Conservation. Springer: 83-96. https://link.springer.com/chapter/10.1007/978-3-642-20992-5_5

Sommer, J. H., Kreft, H., Kier, G, Jetz, W., Mutke, J. & Barthlott, W. 2010 Projected impacts of climate change on regional capacities for global plant species richness.

Proceedings of the Royal Society B. doi: 10.1098/rspb.2010.0120

http://rspb.royalsocietypublishing.org/content/early/2010/03/20/rspb.2010.0120.abstract

Climate change represents a major challenge to the maintenance of global biodiversity. To date, the direction and magnitude of net changes in the global distribution of plant diversity remain elusive. We use the empirical multi-variate relationships between contemporary water-energy dynamics and other non-climatic predictor variables to model the regional capacity for plant species richness (CSR) and its projected future changes. We find that across all analysed Intergovernmental Panel on Climate Change emission scenarios, relative changes in CSR increase with increased projected temperature rise. Between now and 2100, global average CSR is projected to remain similar to today (+0.3%) under the optimistic B1/+1.8°C scenario, but to decrease significantly (−9.4%) under the ‘business as usual’ A1FI/+4.0°C scenario. Across all modelled scenarios, the magnitude and direction of CSR change are geographically highly non-uniform. While in most temperate and arctic regions, a CSR increase is expected, the projections indicate a strong decline in most tropical and subtropical regions. Countries least responsible for past and present greenhouse gas emissions are likely to incur disproportionately large future losses in CSR, whereas industrialized countries have projected moderate increases. Independent of direction, we infer that all changes in regional CSR will probably induce on-site species turnover and thereby be a threat to native floras.

Mutke, J. & J.L. Geffert (2010): Keep on working: the uneven documentation of regional moss floras.

Tropical Bryology 31: 7-13.

http://tropical-bryology.org/Articles/open/VOL31open/Mutke&Geffert_TB31_P7-13.pdf

We analysed documented moss species numbers on a global scale with the aim to identify regions or countries with possibly under-documented moss floras. European units (countries, administrative units) in general have much higher documented species numbers than extra-European units with similar area sizes.

Especially South American and African units have relatively low documented species numbers. This is in contrast to the overall continental moss floras of these regions, which are almost twice as species rich compared to Europe. We identified possibly under-documented geographical units in each continent based on negative outliers in species-area plots. There is a negative correlation of species richness with the area of desert or grassland biomes in a geographical unit. Based on our dataset, the question of the existence of a general latitudinal gradient of increasing moss diversity with decreasing latitude has to be denied.

Jetz, W., Kreft, H., Ceballos, G. & Mutke, J. (2008): Global associations between terrestrial producer and vertebrate consumer diversity. Proceedings of the Royal Society B. January 22, 2009 276:269-278; doi:10.1098/rspb.2008.1005.

http://journals.royalsociety.org/content/073n110482823051/

In both ecology and conservation, often a strong positive association is assumed between the diversity of plants as primary producers and that of animals, specifically primary consumers. Such a relationship has been observed at small spatial scales, and a begetting of diversity by diversity is expected under various scenarios of co-evolution and co-adaptation. But positive producer-consumer richness relationships may also arise from similar associations with past opportunities for diversification or contemporary environmental conditions, or from emerging properties of plant diversity such as vegetation complexity or productivity. Here we assess whether the producer-consumer richness relationship generalizes from plot to regional scale and provide a first global test of its strength for vascular plants and endothermic vertebrates. We find strong positive richness associations, but only limited congruence of the most diverse regions. The richness of both primary and higher-level consumers increases with plant richness at similar strength and rate. Environmental conditions emerge as much stronger predictors of consumer richness, and after accounting for environmental differences little variation is explained by plant diversity. We conclude that biotic interactions and strong local associations between plants and consumers only relatively weakly scale up to broad geographical scales and to functionally diverse taxa, for which environmental constraints on richness dominate.

Kreft, H., Jetz, W., Mutke, J., Kier, G., Barthlott, W. (2008): Global diversity of island floras from a macroecological perspective. Ecology Letters 11, 116-127. doi:10.1111/j.1461-0248.2007.01129.x

http://www.blackwell-synergy.com/doi/abs/10.1111/j.1461-0248.2007.01129.x

 Islands harbour a significant portion of all plant species worldwide. Their biota are often characterized by narrow distributions and are particularly susceptible to biological invasions and climate change. To date, the global richness pattern of islands is only poorly documented and factors causing differences in species numbers remain controversial. Here, we present the first global analysis of 488 island and 970 mainland floras. We test the relationship between island characteristics (area, isolation, topography, climate and geology) and species richness using traditional and spatial models. Area is the strongest determinant of island species numbers (R2 = 0.66) but a weaker predictor for mainlands (R2 = 0.25). Multivariate analyses reveal that all investigated variables significantly contribute to insular species richness with area being the strongest followed by isolation, temperature and precipitation with about equally strong effects. Elevation and island geology show relatively weak yet significant effects. Together these variables account for 85% of the global variation in species richness.

Mutke, J. & Barthlott, W. 2005. Patterns of vascular plant diversity at continental to global scales. Biol. Skr. 55: 521-531. PDF

Patterns of vascular plant diversityThe studies presented in this paper analyse diversity patterns of land plants (mosses, ferns, gymnosperms, and angiosperms) at continental to global scales. A revised version of our earlier world map of vascular plant species richness and the first maps of species richness of mosses and gymnosperms on a global scale are presented. Diversity patterns of vascular plants are correlated with different measures of geodiversity (the diversity of the abiotic environment). Global centres of vascular plant diversity coincide with highly structured, geodiverse areas in the tropics and subtropics. These are the Chocó-Costa Rica region, the tropical eastern Andes and the north western Amazonia, the eastern Brazil, the northern Borneo, and New Guinea, as well as the South African Cape region, southern Mexico, East Himalaya, western Sumatra, Malaysia, and eastern Madagascar. Constraints imposed by the physical environment, such as the length of the thermal vegetation period or water availability, shape large scale trends of biodiversity. However, important centres of species richness and endemism can only be explained when taking into account the history of the floras. The main diversity centres in SE Asia are the same for gymnosperms as for all other vascular plants, but in other parts of the tropics and subtropics there is low gymnosperm diversity. The exceptions to this pattern are Mexico and California, which have almost as many species of gymnosperms as SE Asia. The increase in the number of species and genera published during the last 250 years is documented, based on data from the Index Kewensis. The first continental maps of Cactaceae diversity at species and genus level are used to show how choice of the taxonomic level affects the analysis and its implications for priority setting in biodiversity conservation. In this context, global biodiversity hotspots are discussed and an alternative world map of hotspots is proposed.

Kreft, H. & Jetz, W. (2007): Global patterns and determinants of vascular plant diversity. Proceedings of the National Academy of Sciences (PNAS), 104, 5925-5930.

http://www.pnas.org/cgi/content/abstract/104/14/5925?ck=nck

Plants, with an estimated 300,000 species, provide crucial primary production and ecosystem structure. To date, our quantitative understanding of diversity gradients of mega-diverse clades such as plants has been hampered by the availability of distribution data. Here, we investigate the global-scale species richness pattern of vascular plants and examine its environmental and potential historical determinants. Across 1,032 geographic regions worldwide, potential evapotranspiration, the number of wet days per year, and measures of topographical and habitat heterogeneity emerge as core predictors of species richness.

After accounting for environmental effects, the residual differences across the major floristic kingdoms are minor, with the exception of the uniquely diverse Cape Region, highlighting the important role of historical contingencies. Notably, the South African Cape region contains more than twice as many species as expected by the global environmental model, confirming its uniquely evolved flora. A combined multi-predictor model explains ~70% of the global variation in species richness and fully accounts for the enigmatic latitudinal gradient in species richness. The models illustrate the geographic interplay of different environmental predictors of species richness.

Our findings highlight that different hypotheses about the causes of diversity gradients are not mutually exclusive, but likely act synergistically with water-energy dynamics playing a dominant role. The presented geostatistical approach is likely to prove instrumental for identifying richness patterns of the many other taxa without single-species distribution data that still escape our understanding.

Kreft, H., Sommer, J. H. and Barthlott, W. (2006): The significance of geographic range size for spatial diversity patterns in Neotropical palms. Ecography 29, 21–30.

http://onlinelibrary.wiley.com/doi/10.1111/j.2005.0906-7590.04203.x/full

The significance of geographic range sizeWe examined the effect of range size in commonly applied macroecological analyses using continental distribution data for all 550 Neotropical palm species (Arecaceae) at varying grain sizes from 0.58 to 58. First, we evaluated the relative contribution of range-restricted and widespread species on the patterns of species richness and endemism. Second, we analysed the impact of range size on the predictive value of commonly used predictor variables. Species sequences were produced arranging species according to their range size in ascending, descending, and random order. Correlations between the cumulative species richness patterns of these sequences and environmental predictors were performed in order to analyse the effect of range size. Despite the high proportion of rare species, patterns of species richness were found to be dominated by a minority of widespread species ( /20%) which contained 80% of the spatial information. Climatic factors related to energy and water availability and productivity accounted for much of the spatial variation of species richness of widespread species. In contrast, species richness of range-restricted species was to a larger extent determined by topographical complexity. However, this effect was much more difficult to detect due to a dominant influence of widespread species. Although the strength of different environmental predictors changed with spatial scale, the general patterns and trends proved to be relatively stabile at the examined grain sizes. Our results highlight the difficulties to approximate causal explanations for the occurrence of a majority of species and to distinguish between contemporary climatic factors and history.

Braun, G., Mutke, J., Reder, A. and Barthlott, W. (2002): Biotope patterns, phytodiversity and forestline in the Andes, based on GIS and remote sensing data, 75-89 pp. In Körner C. and Spehn, E. M. (Eds): Mountain Biodiversity: a global assessment, Parthenon Publishing, London.

Biotope patterns in the AndesOn a continental or global scale, it is near to impossible to adequately assess biodiversity and monitor its losses solely by collecting ground data. Even at the regional scale, the difficulties are so immense that we hardly have any data for tropical and subtropical high mountains. In this paper, we illustrate how a combination of biological field data with remote sensing data and climatological, pedological and topological GIS data can be used to obtain large-scale phytodiversity patterns. The tropical Andes are one of the hot spots of biological diversity (Barthlott et al., 1996, 1999; Davis et al., 1997; Myers et al., 2000; Groombridge and Jenkins, 2000). Together with their foothills, the Andes cover an area of nearly 8.1 million km2 and stretch from about 11° 30' N to 55° 05' S. Elevations above 4000 m reach a maximum in Peru, Bolivia and Argentina. The Andean complex north of the equator forms two or three ranges nearly reaching 10° N in Venezuela. A remarkable decline in altitude can be observed between Ecuador and Peru, where elevation does not exceed 4000. Mittermeyer et al. (1999) estimate that 45 000 species of vascular plants (a sixth of the global flora) live in the Andean region. For example, in the Peruvian Andes above 500 m, more than 200 families of flowering plants can be found according to the checklist of Brako and Zarucchi (1993). This is 20% more than in the Peruvian Amazon and 20% more than in the whole flora of Europe (Tutin et al., 1968–1993) which covers an area more than 20 times as large. A major cause of this enormous regional biological richness is the compression of climatic life zones along elevational gradients. On a global scale, a distinct increase of vascular plant diversity can be observed as one approaches the equator (Figure 6.1).

Phytodiversity increases with increasing warmth and humidity as one moves from the poles to the equator, except for continental and coastal deserts. Secondary maxima of species richness can be found in both hemispheres between 30° and 35°, due to Mediterranean type ecosystems and subtropical evergreen forests. On a regional scale, topographic heterogeneity becomes a second important driver. Mountains act as barriers for advective atmospheric moisture and front ranges trap much of the water with often little left for inner chains or leeward slopes. As temperatures decrease with elevation, the well known altitudinal and vertical arrangement of ecoclimatological zones emerges (Lauer, 1986). Many authors have investigated the altitudinal zonation of the Andean vegetation and flora (e.g. Humboldt, 1805–1834; Weberbauer, 1911; Acosta-Solís, 1968; Ellenberg, 1975; Cleef et al., 1984). However, it was only in the last decade that large floristic databases (e.g. Brako and Zarucchi, 1993; Jørgensen and León-Yánez, 1999) allowed detailed quantitative comparisons of floristical zones and altitudinal gradients. In addition, data scattered in the literature regarding small but very detailed floristic inventories, especially for woody plants, were collected in databases and synoptically analysed by different authors (e.g. Clinebell et al., 1995; Terborgh and Andresen, 1999; Mutke, unpublished).

Nested in these larger climatic gradients, steepness and aspect of slopes and micro-relief create a topographical diversity which interacts with solar irradiance, wind and precipitation, creating a multitude of habitats, here addressed as 'geodiversity'. The geodiversity of mountains by far exceeds that of lowlands and in part explains the high mountain biodiversity. Geodiversity is defined herein as the spatial heterogeneity of atmospheric and geospheric conditions (e.g. petrography, soils, topography and associated microclimate). In a given area, geodiversity reflects the multitude of life conditions and thus affects total regional biological diversity. The total diversity of an area, the ecodiversity, consists of biodiversity and geodiversity (Barthlott et al., 1996, 2000). We prefer the term ecodiversity rather than landscape diversity, as the latter is not free of scale. Geodiversity may become ecologically effective at the centimetre scale. Hence, it is possible to describe the ecodiversity of, e.g. a cubic centimetre of soil, including highly diverse microbial communities – a scale not covered by the term landscape diversity. Additionally, in biodiversity research the term landscape diversity has long been used as a synonym for the gamma diversity (Whittaker, 1972, 1977), the mere biodiversity at landscape level, without taking into account geodiversity.

Barthlott, W., Kier, G. and Mutke, J. (1999): Globale Artenvielfalt und ihre ungleiche Verteilung. Courier Forschungsinstitut Senckenberg 215, 7-22.

Comparison of species numbers of vascular plants (following WRI 1997) to a) the sum of species numbers of tetrapods on the country level (by WRI 1997), b) estimated species numbers of insects for different regions (countries, archipelagos) world-wide (based on Table 4.5 in Gaston 1996).