Multiscale climate change impacts on plant diversity in the Atacama Desert

Comprehending ecological dynamics requires not only knowledge of modern communities but also detailed reconstructions of ecosystem history. Ancient DNA (aDNA) metabarcoding allows biodiversity responses to major climatic change to be explored at different spatial and temporal scales. We extracted aDNA preserved in fossil rodent middens to reconstruct late Quaternary vegetation dynamics in the hyperarid Atacama Desert. By comparing our paleo‐informed millennial record with contemporary observations of interannual variations in diversity, we show local plant communities behave differentially at different timescales. In the interannual (years to decades) time frame, only annual herbaceous expand and contract their distributional ranges (emerging from persistent seed banks) in response to precipitation, whereas perennials distribution appears to be extraordinarily resilient. In contrast, at longer timescales (thousands of years) many perennial species were displaced up to 1,000 m downslope during pluvial events. Given ongoing and future natural and anthropogenically induced climate change, our results not only provide baselines for vegetation in the Atacama Desert, but also help to inform how these and other high mountain plant communities may respond to fluctuations of climate in the future.     

A High-Resolution Chronology of Rapid Forest Transitions following Polynesian Arrival in New Zealand

Human-caused forest transitions are documented worldwide, especially during periods when land use by dense agriculturally-based populations intensified. However, the rate at which prehistoric human activities led to permanent deforestation is poorly resolved. In the South Island, New Zealand, the arrival of Polynesians c. 750 years ago resulted in dramatic forest loss and conversion of nearly half of native forests to open vegetation. This transformation, termed the Initial Burning Period, is documented in pollen and charcoal records, but its speed has been poorly constrained. High-resolution chronologies developed with a series of AMS radiocarbon dates from two lake sediment cores suggest the shift from forest to shrubland occurred within decades rather than centuries at drier sites. We examine two sites representing extreme examples of the magnitude of human impacts: a drier site that was inherently more vulnerable to human-set fires and a wetter, less burnable site. The astonishing rate of deforestation at the hands of small transient populations resulted from the intrinsic vulnerability of the native flora to fire and from positive feedbacks in post-fire vegetation recovery that increased landscape flammability. Spatially targeting burning in highly-flammable seral vegetation in forests rarely experiencing fire was sufficient to create an alternate fire-prone stable state. The New Zealand example illustrates how seemingly stable forest ecosystems can experience rapid and permanent conversions. Forest loss in New Zealand is among the fastest ecological transitions documented in the Holocene; yet equally rapid transitions can be expected in present-day regions wherever positive feedbacks support alternate fire-inhibiting, fire-prone stable states.     

High-resolution coproecology: using coprolites to reconstruct the habits and habitats of New Zealand's extinct upland moa (Megalapteryx didinus)

Knowledge about the diet and ecology of extinct herbivores has important implications for understanding the evolution of plant defence structures, establishing the influences of herbivory on past plant community structure and composition, and identifying pollination and seed dispersal syndromes. The flightless ratite moa (Aves: Dinornithiformes) were New Zealand's largest herbivores prior to their extinction soon after initial human settlement. Here we contribute to the knowledge of moa diet and ecology by reporting the results of a multidisciplinary study of 35 coprolites from a subalpine cave (Euphrates Cave) on the South Island of New Zealand. Ancient DNA analysis and radiocarbon dating revealed the coprolites were deposited by the extinct upland moa (Megalapteryx didinus), and span from at least 6,368±31 until 694±30 (14)C years BP; the approximate time of their extinction. Using pollen, plant macrofossil, and ancient DNA analyses, we identified at least 67 plant taxa from the coprolites, including the first evidence that moa fed on the nectar-rich flowers of New Zealand flax (Phormium) and tree fuchsia (Fuchsia excorticata). The plant assemblage from the coprolites reflects a highly-generalist feeding ecology for upland moa, including browsing and grazing across the full range of locally available habitats (spanning southern beech (Nothofagus) forest to tussock (Chionochloa) grassland). Intact seeds in the coprolites indicate that upland moa may have been important dispersal agents for several plant taxa. Plant taxa with putative anti-browse adaptations were also identified in the coprolites. Clusters of coprolites (based on pollen assemblages, moa haplotypes, and radiocarbon dates), probably reflect specimens deposited at the same time by individual birds, and reveal the necessity of suitably large sample sizes in coprolite studies to overcome potential biases in diet interpretation.     

Interspecies interference and monitoring duration affect detection rates in chew cards

Pest monitoring methods should provide unbiased accurate estimates of pest densities and locations, while also minimizing time‐in‐field and costs. Recent pest mammal monitoring studies have found that chew cards are more effective than conventional mammal monitoring methods, but little experimental work has been done to determine optimal experimental duration or quantify the risks of saturation by one species biasing detections of other species. Here, we used chew cards in three sites within Awarua wetland (Southland, New Zealand) to investigate the optimal amount of time required to detect targeted pest species (rats, possums and mice), and to examine the potential of rats and possums to bias detection rates of other species. We found depressed detections of possums and rats where a contraspecific had been detected on a card, which is consistent with previous studies of a similar duration on interspecies interference. This experiment is the first to analyse the rates at which species detections accrue over the course of a survey, and we found rat detections lagged behind possums for the first four nights. We modelled the effect of survey duration and relative rat abundance on the likelihood of further possum detections. Duration and rat abundance interacted, meaning there are trade‐offs to be considered with regard to duration: shorter durations may avoid the risk of saturation in areas of high pest density, but risk not sampling sparse or neophobic populations. Our data suggest that chew cards remain one of the most sensitive pest monitoring tools for rats and possums, compared to conventional methods such as tracking tunnels and wax tags. In areas of moderate pest densities, we suggest that a duration of five nights is optimal for detecting pests. However, in areas of high pest density the sensitivity of chew cards may render them unsuitable because of saturation and interspecies interference effects.     

Patch selection by red deer in relation to energy and protein intake: a re-evaluation of Langvatn and Hanley's (1993) results

Langvatn and Hanley (1993) recently reported that patch use by red deer (Cervus elaphus) was more strongly correlated with short term rates of intake of digestible protein than dry matter. Such short term measures overlook effects of gut filling, which may constrain intake by ruminants over longer time scales (i.e., daily rates of gain). We reanalyzed Langvatn and Hanley's data using an energy intake model incorporating such a processing constraint, to determine whether their conclusions are robust. We found that the use of patches by red deer was just as strongly correlated with an estimate of the daily rate of intake of digestible energy as one of digestible protein during four out of seven trials, but slightly lower in three out of seven trials. In all cases, daily intake of digestible energy was a much better predictor of patch preference by red deer than was the intake of dry matter. Our reanalysis suggests that the daily intake of energy was highly correlated with that of protein in these trials, as may often be the case for herbivores feeding on graminoids. Hence the observed pattern of patch use by red deer could simultaneously enhance rates of both protein and energy intake.     

Detecting the initial impact of humans and introduced species on island environments in Remote Oceania using palaeoecology

The isolated archipelagos of Remote Oceania provide useful microcosms for understanding the impacts of initial human colonization. Palaeoecological data from most islands reveal catastrophic transformations, with losses of many species through over-hunting, deforestation and the introduction of novel mammalian predators, the most ubiquitous and devastating being commensal rats. Two case studies from the Austral Islands and New Zealand demonstrate the potential of direct human proxies from palaeoecological archives to detect initial human impacts on islands. We show how pollen from introduced crop plants, and buried seeds with gnaw marks from the introduced Pacific rat (Rattus exulans) provide a reliable means of detecting initial human colonization and highlight the downstream ecological consequences of agriculture and rat introduction on previously uninhabited pristine island ecosystems. Previous studies have relied on indirect signals of human arrival based on charcoal and associated vegetation changes, the causes of which are often more difficult to interpret with certainty.