Macro-zooplankter responses to simulated climate warming in experimental freshwater microcosms

1. We report data collected from 48 replicated microcosm communities created to mimic plant‐dominated shallow lake and pond environments. Over a 2‐year period, the microcosms were subjected to warming treatments (continuous 3 °C above ambient and 3 °C above ambient during summer only), a nutrient addition treatment and the presence or absence of fish. We tracked macro‐zooplankter dynamics, censusing cladoceran populations at the species level, copepods at the order level and ostracods as a class. 2. Responses to warming were subtle. Cladoceran diversity and overall abundance were not significantly affected by warming, although measures of community evenness increased. Warming effects on patterns of population trajectories tended to be strongly seasonal and most apparent during periods of pronounced increase. Populations of the prevalent cladocerans, Chydorus sphaericus and Simocephalus vetulus, displayed idiosyncratic patterns, with evidence in the case of S. vetulus for a negative relationship between warming and body‐size at maturity. Copepod populations were reduced in size by warming, but those of ostracods increased. 3. The effects of the nutrient addition and fish treatments were strong and consistent, interacting little with warming effects in statistical models. Zooplankter abundance tended to be the highest in the fish‐free microcosms receiving additional nutrient inputs and lowest when fish were present and no nutrients were added. Both treatments reduced cladoceran diversity and community evenness. 4. We suggest that warming, independently, is unlikely to supplant the effects of changing nutrient loading and fish predation as the major driver of zooplankter dynamics in shallow lakes and ponds. Moreover, in the situations where warming was of significant influence in our experiment, the distinction between summer‐only warming and year‐around warming was blurred. This suggests that warming effects were most pervasive during the summer, at the upper end of the temperature spectrum.     

Assessing the role of bark- and wood-boring insects in the decline of Scots pine (Pinus sylvestris) in the Swiss Rhone valley

Abstract.  1. In several dry inner Alpine valleys higher mortality levels of pine have been observed in recent years. This paper evaluates the role of xylophagous insects in the current pine decline and the influence of climate change on the infestation dynamics.
2. More than 200 trees of different levels of crown transparency (needle loss) were felled between 2001 and 2005 and sections of them incubated in insect emergence traps. Colonisation densities were related to the transparency level of each host tree at the time of attack.
3. Trees with more than 80% needle loss were colonised most frequently, but the breeding density was highest in trees with 65–80% needle loss.
4. The scolytine Ips acuminatus and the buprestid Phaenops cyanea colonised trees with 30–90% needle loss in high densities. The bark beetle Tomicus minor was less aggressive, preferring trees with 60–85% needle loss. The hymenopteran Sirex noctilio and the cerambycid Acanthocinus aedilis were restricted to greatly weakened trees with 50–85% needle loss. Most species colonised trees that had experienced a decline in vigour, that is an increase in crown transparency shortly before attack.
5. The infestation dynamics of P. cyanea covaried with the drought index as well as with temperature.
6. Increased temperatures not only trigger a drought stress rendering the host trees susceptible to insect attack, but also accelerate insect development. As more frequent drought periods are likely as a result of climate change, even trees only slightly or temporarily weakened will be more subject to attack by aggressive species such as I. acuminatus and P. cyanea .     

Mass mortality in Northwestern Mediterranean rocky benthic communities: effects of the 2003 heat wave

Late in summer 2003, extensive mass mortality of at least 25 rocky benthic macro-invertebrate species (mainly gorgonians and sponges) was observed in the entire Northwestern (NW) Mediterranean region, affecting several thousand kilometers of coastline. We were able to characterize the mortality event by studying six areas covering the main regions of the NW Mediterranean basin. The degree of impact on each study area was quantified at 49 sites by estimating the proportion of colonies affected in populations of several gorgonian species compared with reference data obtained in years without mortality signs. According to these data, the western areas (Catalan coast and Balearic Islands) were the least affected, while the central areas (Provence coast and Corsica-Sardinia) showed a moderate impact. The northernmost and eastern areas (Gulf of Genoa and Gulf of Naples) displayed the highest impact, with almost 80% of gorgonian colonies affected. The heat wave of 2003 in Europe caused an anomalous warming of seawater, which reached the highest temperatures ever recorded in the studied regions, between 1 and 3 °C above the climatic values (mean and maximum). Because this exceptional warming was observed in the depth ranges most affected by the mortality, it seems likely that the 2003 anomalous temperature played a key role in the observed mortality event. A correlation analysis between temperature conditions and degree of impact seems to support this hypothesis. Under the present climate warming trend, new mass mortality events may occur in the near future, possibly driving a major biodiversity crisis in the Mediterranean Sea.     

The impacts of climate change on the annual cycles of birds

Organisms living today are descended from ancestors that experienced considerable climate change in the past. However, they are currently presented with many new, man-made challenges, including rapid climate change. Migration and reproduction of many avian species are controlled by endogenous mechanisms that have been under intense selection over time to ensure that arrival to and departure from breeding grounds is synchronized with moderate temperatures, peak food availability and availability of nesting sites. The timing of egg laying is determined, usually by both endogenous clocks and local factors, so that food availability is near optimal for raising young. Climate change is causing mismatches in food supplies, snow cover and other factors that could severely impact successful migration and reproduction of avian populations unless they are able to adjust to new conditions. Resident (non-migratory) birds also face challenges if precipitation and/or temperature patterns vary in ways that result in mismatches of food and breeding. Predictions that many existing climates will disappear and novel climates will appear in the future suggest that communities will be dramatically restructured by extinctions and changes in range distributions. Species that persist into future climates may be able to do so in part owing to the genetic heritage passed down from ancestors who survived climate changes in the past.     

Fish and fisheries in hot water: What is happening and how do we adapt?

Rapid climate changes are currently driving substantial reorganizations of marine ecosystems around the world. A key question is how these changes will alter the provision of ecosystem services from the ocean, particularly from fisheries. To answer this question, we need to understand not only the ecological dynamics of marine systems, but also human adaptation and feedbacks between humans and the rest of the natural world. In this review, we outline what we have learned from research primarily in continental shelf ecosystems and fishing communities of North America. Key findings are that marine animals are highly sensitive to warming and are responding quickly to changes in water temperature, and that such changes are often happening faster than similar processes on land. Changes in species distributions and productivity are having substantial impacts on fisheries, including through changing catch compositions and longer distances traveled for fishing trips. Conflicts over access to fisheries have also emerged as species distributions are no longer aligned with regulations or catch allocations. These changes in the coupled natural-human system have reduced the value of ecosystem services from some fisheries and risk doing so even more in the future. Going forward, substantial opportunities for more effective fisheries management and operations, marine conservation, and marine spatial planning are likely possible through greater consideration of climate information over time-scales from years to decades.     

Vertical partitioning between sister species of Rhizopogon fungi on mesic and xeric sites in an interior Douglas‐fir forest

Understanding ectomycorrhizal fungal (EMF) community structure is limited by a lack of taxonomic resolution and autecological information. Rhizopogon vesiculosus and Rhizopogon vinicolor (Basidiomycota) are morphologically and genetically related species. They are dominant members of interior Douglas‐fir (Pseudotsuga menziesii var. glauca) EMF communities, but mechanisms leading to their coexistence are unknown. We investigated the microsite associations and foraging strategy of individual R. vesiculosus and R. vinicolor genets. Mycelia spatial patterns, pervasiveness and root colonization patterns of fungal genets were compared between Rhizopogon species and between xeric and mesic soil moisture regimes. Rhizopogon spp. mycelia were systematically excavated from the soil and identified using microsatellite DNA markers. Rhizopogon vesiculosus mycelia occurred at greater depth, were more spatially pervasive, and colonized more tree roots than R. vinicolor mycelia. Both species were frequently encountered in organic layers and between the interface of organic and mineral horizons. They were particularly abundant within microsites associated with soil moisture retention. The occurrence of R. vesiculosus shifted in the presence of R. vinicolor towards mineral soil horizons, where R. vinicolor was mostly absent. This suggests that competition and foraging strategy may contribute towards the vertical partitioning observed between these species. Rhizopogon vesiculosus and R. vinicolor mycelia systems occurred at greater mean depths and were more pervasive in mesic plots compared with xeric plots. The spatial continuity and number of trees colonized by genets of each species did not significantly differ between soil moisture regimes.     

Drought and the consequences of El Niño in Borneo: a case study of figs

Borneo has a perhumid climate but occasional severe droughts have an important impact. Droughts may affect the composition and size structure of plant communities through differential mortality or, via their impact on the availability of plant resources, affect plant–animal interactions. From January to April 1998, northern Borneo suffered a very severe drought linked to the El Niño Southern Oscillation event of 1997–1998. In this article, the impacts of this drought on the rain forest at Lambir Hills National Park, Sarawak, are considered with special reference to a keystone plant group, the figs. Small fires entered the edge of the forest from the roadside, killing saplings, climbers, and understory trees. Community-wide mortality for adult trees was 0–7 times higher than in nondrought years, with larger trees showing a greater proportional increase. In figs, mortality was significantly higher in pioneers, but hemiepiphytes and roadside species were unaffected. Phenology was substantially affected. Leaf and flower/fruit production decreased or ceased during the drought and increased suddenly following renewed rain. Pollinators of dioecious figs became locally extinct during the drought, and other plant–animal interactions may also have been disrupted. The frequency and severity of droughts has increased substantially in the past three decades, and climate models suggest this may be the result of global warming. The impacts of the 1998 drought at Lambir Hills National Park suggest that, should this trend continue, a substantial alteration of habitats and overall loss of biodiversity can be expected in Borneo.     

Seasonal dispersal of pests: one surge or two?

Many agricultural pest species occur in seasonal metapopulations with a period of asexual reproduction. We use evolutionary theory to predict timing of dispersal for such species, and identify four sequential phases: no dispersal, dispersal from initially occupied patches, dispersal from later colonized patches, and no dispersal. The third type of phase occurs only when reproductive rates are relatively high; we speculate that this could explain why among aphids there can be either one or two waves of dispersal during a season, depending on the species. Our model also explains other features of aphid biology, including a summer crash in colony size, and a decline in the number of colonies towards the end of each reproductive season. The presence of an additional surge of dispersal becomes more likely as season length increases, and does not require further evolution. This could have profound implications for pest management during future climatic warming.     

Aphid and host‐plant genotype × genotype interactions under elevated CO2

1. Elevated CO₂ can alter plant physiology and morphology, and these changes are expected to impact diet quality for insect herbivores. While the plastic responses of insect herbivores have been well studied, less is known about the propensity of insects to adapt to such changes. Genetic variation in insect responses to elevated CO₂ and genetic interactions between insects and their host plants may exist and provide the necessary raw material for adaptation. 2. We used clonal lines of Rhopalosiphum padi (L.) aphids to examine genotype‐specific responses to elevated CO₂. We used the host plant Schedonorus arundinaceus (tall fescue; Schreb), which is capable of asexual reproduction, to investigate host plant genotype‐specific effects and possible host plant‐by‐insect genotype interactions. The abundance and density of three R. padi genotypes on three tall fescue genotypes under three concentrations of CO₂ (ambient, 700, and 1000 ppm) in a controlled greenhouse environment were examined. 3. Aphid abundance decreased in the 700 ppm CO₂ concentration, but increased in the 1000 ppm concentration relative to ambient. The effect of CO₂ on aphid density was dependent on host plant genotype; the density of aphids in high CO₂ decreased for two plant genotypes but was unchanged in one. No interaction between aphid genotype and elevated CO₂ was found, nor did we find significant genotype‐by‐genotype interactions. 4. This study suggests that the density of R. padi aphids feeding on tall fescue may decrease under elevated CO₂ for some plant genotypes. The likely impact of genotype‐specific responses on future changes in the genetic structure of plant and insect populations is discussed.