Richard B. Primack

Phylogenetic patterns of species loss in Thoreau's woods are driven by climate change

Climate change has led to major changes in the phenology (the timing of seasonal activities, such as flowering) of some species but not others. The extent to which flowering-time response to temperature is shared among closely related species might have important consequences for community-wide patterns of species loss under rapid climate change. Henry David Thoreau initiated a dataset of the Concord, Massachusetts, flora that spans ≈150 years and provides information on changes in species abundance and flowering time. When these data are analyzed in a phylogenetic context, they indicate that change in abundance is strongly correlated with flowering-time response. Species that do not respond to temperature have decreased greatly in abundance, and include among others anemones and buttercups [Ranunculaceae pro parte (p.p.)], asters and campanulas (Asterales), bluets (Rubiaceae p.p.), bladderworts (Lentibulariaceae), dogwoods (Cornaceae), lilies (Liliales), mints (Lamiaceae p.p.), orchids (Orchidaceae), roses (Rosaceae p.p.), saxifrages (Saxifragales), and violets (Malpighiales). Because flowering-time response traits are shared among closely related species, our findings suggest that climate change has affected and will likely continue to shape the phylogenetically biased pattern of species loss in Thoreaus woods.

Leaf‐out phenology of temperate woody plants: from trees to ecosystems

Leafing-out of woody plants begins the growing season in temperate forests and is one of the most important drivers of ecosystem processes. There is substantial variation in the timing of leaf-out, both within and among species, but the leaf development of almost all temperate tree and shrub species is highly sensitive to temperature. As a result, leaf-out times of temperate forests are valuable for observing the effects of climate change. Analysis of phenology data from around the world indicates that leaf-out is generally earlier in warmer years than in cooler years and that the onset of leaf-out has advanced in many locations. Changes in the timing of leaf-out will affect carbon sequestration, plant-animal interactions, and other essential ecosystem processes. The development of remote sensing methods has expanded the scope of leaf-out monitoring from the level of an individual plant or forest to an entire region. Meanwhile, historical data have informed modeling and experimental studies addressing questions about leaf-out timing. For most species, onset of leaf-out will continue to advance, although advancement may be slowed for some species because of unmet chilling requirements. More information is needed to reduce the uncertainty in predicting the timing of future spring onset.

Community studies in pollination ecology in the high temperate Andes of Central Chile. II: Effect of temperature on visitation rates and pollination possibilities

Visitation rates and mean numbers of visits per flower per day are determined at three altitudinal levels (2 200–3 600 m) in the high Andes of central Chile from quantified observations of flowers visitors to a total of 134 species of plants, studied over three flowering seasons. Significant altitudinal decreases in the mean no. visits/flower/minute and per day were recorded, with Level III flowers, on the average, being pollinated only about 1/2 as frequently and to as low as 1/4 as frequently in certain months, as Level I flowers. Visitation rates are generally highest in early and mid-summer at all altitudes. — The lower visitation rates at the higher elevations are due to lower insect abundance relative to plant resources and lower levels of activity for the insects present, stemming from the generally lower ambient temperatures. Seasonal differences in visitation rates may also be related to differences in insect abundance levels. The total probability of ovule pollination cannot be estimated directly from the pollination rates, because stigmas are probably receptive for longer periods at the higher elevations. When differences in the duration of stigma receptivity are estimated from differences in flower lifelength, the probability of pollination in Level III is not very different from that expected in Level I. However, for some months, the deficit in Level III may still be substantial. — These results underline the inherent dangers of predicting pollination possibilities directly from pollination rates. They also suggest that the impoverished pollination conditions assumed in hypotheses predicting higher amounts of self-compatibility at high altitudes might not be justified for all high temperate mountains.

The history of public participation in ecological research

Members of the public have for centuries recorded their observations of the natural world, including plant and animal distribution and phenology, water quality, weather data, and astronomical phenomena. Given the relatively recent growth of ecological research as a professional field of study, the historical contributions of amateurs to ecology can be easily overlooked. To better understand long-term changes in ecosystems, researchers are now revisiting many of these historical datasets collected by non-professionals. Over the past 100 years, scientific organizations have increasingly included volunteers in large-scale monitoring projects to broaden the geographical extent and sample size of observations. We believe that a renewed interest in citizen science, enriched with the perspective and data provided by the long tradition of public participation in science, will broaden the engagement of the public in ecological research and lead to new scientific insights.

Herbarium specimens demonstrate earlier flowering times in response to warming in Boston

Museum specimens collected in the past may be a valuable source of information on the response of species to climate change. This idea was tested by comparing the flowering times during the year 2003 of 229 living plants growing at the Arnold Arboretum in Boston, Massachusetts, USA, with 372 records of flowering times from 1885 to 2002 using herbarium specimens of the same individual plants. During this period, Boston experienced a 1.5°C increase in mean annual temperature. Flowering times became progressively earlier; plants flowered 8 d earlier from 1980 to 2002 than they did from 1900 to 1920. Most of this shift toward earlier flowering times is explained by the influence of temperature, especially temperatures in the months of February, March, April, and May, on flowering time. Plants with a long flowering duration appear to be as useful for detecting responses to changing temperatures as plants with a short flowering duration. Additional studies using herbarium specimens to detect responses to climate change could examine specimens from specific, intensively collected localities, such as mountain peaks, islands, and unique habitats.

Costs of Reproduction in the Pink Lady's Slipper Orchid: A Four-Year Experimental Study

The cost of current reproduction on future growth, survival, and reproduction is a central concept in evolutionary ecology, but the field evidence in plants for a cost of reproduction is weak because the appropriate experimental protocol (manipulation of the level of reproduction in an experimental group of individuals) has rarely been carried out. The pink ladys slipper orchid, Cypripedium acaule, is well suited to this design because naturally occurring flowering plants only rarely fruit, whereas virtually all hand-pollinated flowers develop into fruits. In two eastern Massachusetts populations, plants were randomly assigned to be hand-pollinated or left as controls, with the treatments repeated in four successive years. After 2 yr, treatment effects were weak at one site and absent from the other site. By the third and fourth years, the high cost of reproduction was clearly demonstrated in a lower growth and flowering rate of hand-pollinated plants in comparison with the control plants. An average-sized plant that produces a fruit in the current year results in an estimated 10%-13% decrease in leaf area and a 5%-16% decrease in the probability of flowering in the following year. Plants that are experimentally defoliated are still capable of maturing their fruit, even though these plants have a decreased probability of flowering in the following year. These results show that long-term studies in the field are capable of demonstrating a cost of reproduction.

The Three Gorges Dam: an ecological perspective

The Three Gorges Dam in China is the largest dam ever built. Its impacts on the biodiversity and ecological processes in the region are causing concern to ecologists worldwide. The dam and associated environmental alterations may result in a number of regional changes in terrestrial and aquatic biodiversity, as well as in ecosystem structure and functioning. The dam may also provide a rare opportunity for a grand-scale experiment in habitat fragmentation, allowing ecologists to develop and test a series of hypotheses concerning the dynamics of biodiversity and biotic communities and their responses to disturbances. Such research can help improve conservation practices, stimulate international collaborations, and promote public education on the environment.

VARIATION IN THE PHENOLOGY OF NATURAL POPULATIONS OF MONTANE SHRUBS IN NEW ZEALAND

SUMMARY (1) Variation in flowering time of individuals in one population of each of three species of shrub was recorded over two growing seasons in montane scrub-grassland in the South Island of New Zealand. (2) There was considerable variation in flowering time within each popuLlation, but the flowering rank-order of individuals in different years was positively correlated. (3) Variation in flowering time was poorly correlated witlh the dLuration of flowering and the number of flowers and fruits per plant, except that variation in flowering time in Discaria toumatou (Rhamnaceae) was weakly positively correlated with the percentage fruit set in 1976-77. If both earlier and later flowering plants showed reduced fruit set this would suggest stabilizing selection, but there is no indication of such a pattern. Weak and inconsistent directional phenotypic selection for flowering time can be demonstrated for these two species however. (4) In the warm, dry summer of 1977-78, Leptospermum scoparium (Myrtaceae) and Dracophyllumn spp. (Epacridaceae) flowered on average 9 days and 5 days earlier respectively and for 17 and 8 days shorter duration than in the cool, damp summer of 1976-77. Further, L. scoparium plants had a lower production of flowers and fruits in the second season in comparison with the first season. Plants of Discaria toumatou also flowered earlier in 1977-78, but the duration of flowering and flower and fruit production was greater in 1977-78 than in the 1976-77 season. (5) Patterns of variation in flowering time are also apparent among adjacent populations depending on altitude and on the major geographical units of the range of species. Variation in flowering time both at the individual and the population level may be an important adaptation by which selection and physiological mechanisms increase reproductive success.

Favorable climate change response explains non-native species' success in Thoreau's woods.

Invasive species have tremendous detrimental ecological and economic impacts. Climate change may exacerbate species invasions across communities if non-native species are better able to respond to climate changes than native species. Recent evidence indicates that species that respond to climate change by adjusting their phenology (i.e., the timing of seasonal activities, such as flowering) have historically increased in abundance. The extent to which non-native species success is similarly linked to a favorable climate change response, however, remains untested. We analyzed a dataset initiated by the conservationist Henry David Thoreau that documents the long-term phenological response of native and non-native plant species over the last 150 years from Concord, Massachusetts (USA). Our results demonstrate that non-native species, and invasive species in particular, have been far better able to respond to recent climate change by adjusting their flowering time. This demonstrates that climate change has likely played, and may continue to play, an important role in facilitating non-native species naturalization and invasion at the community level.

Photographs and herbarium specimens as tools to document phenological changes in response to global warming

Global warming is affecting natural systems across the world. Of the biological responses to warming, changes in the timing of phenological events such as flowering are among the most sensitive. Despite the recognized importance of phenological changes, the limited number of long-term records of phenological events has restricted research on the topic in most areas of the world. In a previous study in Boston (American Journal of Botany 91: 1260-1264), we used herbarium specimens and one season of field observations to show that plants flowered earlier as the climate warmed over the past 100 yr. In our new study, we found that two extra years of data did not strengthen the explanatory power of the analysis. Analysis of herbarium specimens without any field data yielded results similar to analyses that included field observations. In addition, we found that photographs of cultivated and wild plants in Massachusetts, data similar to that contained in herbarium specimens, show changes in flowering times that closely match independent data on the same species in the same locations. Dated photographs of plants in flower represent a new resource to extend the range of species and localities addressed in global-warming research.