The ecological consequences of megafaunal loss: giant tortoises and wetland biodiversity

The giant tortoises of the Galapagos have become greatly depleted since European discovery of the islands in the 16th Century, with populations declining from an estimated 250000 to between 8000 and 14000 in the 1970s. Successful tortoise conservation efforts have focused on species recovery, but ecosystem conservation and restoration requires a better understanding of the wider ecological consequences of this drastic reduction in the archipelago's only large native herbivore. We report the first evidence from palaeoecological records of coprophilous fungal spores of the formerly more extensive geographical range of giant tortoises in the highlands of Santa Cruz Island. Upland tortoise populations on Santa Cruz declined 500-700years ago, likely the result of human impact or possible climatic change. Former freshwater wetlands, a now limited habitat-type, were found to have converted to Sphagnum bogs concomitant with tortoise loss, subsequently leading to the decline of several now-rare or extinct plant species.

Persistence of Artemisia steppe in the Tangra Yumco Basin, west-central Tibet, China: despite or in consequence of Holocene lake-level changes?

The closed Tangra Yumco Basin underwent the strongest Quaternary lake-level changes so far recorded on the Tibetan Plateau. It was hitherto unknown what effect this had on local Holocene vegetation development. A 3.6-m sediment core from a recessional lake terrace at 4,700 m a.s.l., 160 m above the present lake level of Tangra Yumco, was studied to reconstruct Holocene flooding phases (sedimentology and ostracod analyses), vegetation dynamics and human influence (palynology, charcoal and coprophilous fungi analyses). Peat at the base of the profile proves lake level was below 4,700 m a.s.l. during the Pleistocene/Holocene transition. A deep-lake phase started after 11 cal ka BP, but the ostracod record indicates the level was not higher than similar to 4,720 m a.s.l. (180 m above present) and decreased gradually after the early Holocene maximum. Additional sediment ages from the basin suggest recession of Tangra Yumco from the coring site after 2.6 cal ka BP, with a shallow local lake persisting at the site until similar to 1 cal ka BP. The final peat formation indicates drier conditions thereafter. Persistence of Artemisia steppe during the Holocene lake high-stand resembles palynological records from west Tibet that indicate early Holocene aridity, in spite of high lake levels that may have resulted from meltwater input. Yet pollen assemblages indicate humidity closer to that of present potential forest areas near Lhasa, with 500-600 mm annual precipitation. Thus, the early mid-Holocene humidity was sufficient to sustain at least juniper forest, but Artemisia dominance persisted as a consequence of a combination of environmental disturbances such as (1) strong early Holocene climate fluctuations, (2) inundation of habitats suitable for forest, (3) extensive water surfaces that served as barriers to terrestrial diaspore transport from refuge areas, (4) strong erosion that denuded the non-flooded upper slopes and (5) increasing human influence since the late glacial.

Interactions of climate and land use documented in the varved sediments of Seebergsee in the Swiss Alps

This paper presents a multiproxy high-resolution study of the past 2600 years for Seebergsee, a small Swiss lake with varved sediments at the present tree-line ecotone. The laminae were identified as varves by a numerical analysis of diatom counts in the thin-sections. The hypothesis of two diatom blooms per year was corroborated by the 210Pb and 137Cs chronology. A period of intensive pasturing during the ‘Little Ice Age’ between ad 1346 and ad 1595 is suggested by coprophilous fungal spores, as well as by pollen indicators of grazing, by the diatom-inferred total phosphorus, by geochemistry and by documentary data. The subsequent re-oligotrophication of the lake took about 88 years, as determined by the timelag between the decline of coprophile fungal spores and the restoration of pre-eutrophic nutrient conditions. According to previous studies of latewood densities from the same region, cold summers around ad 1600 limited the pasturing at this altitude. This demonstrated the socio-economic impact of a single climatic event. However, the variance partitioning between the effects of land use and climate, which was applied for the whole core, revealed that climate independent of land use and time explained only 1.32% of the diatom data, while land use independent of climate and time explained 15.7%. Clearly land use in‘ uenced the lake, but land use was not always driven by climate. Other factors beside climate, such as politics or the introduction of fertilizers in the seventeenth and eighteenth centuries also in‘ uenced the development of Alpine pasturing.