Mast-seeding plants often produce high seed crops the year after a warm spring or summer, but the warm-temperature model has inconsistent predictive ability. Here, we show for 26 long-term data sets from five plant families that the temperature difference between the two previous summers (ΔT) better predicts seed crops. This discovery explains how masting species tailor their flowering patterns to sites across altitudinal temperature gradients; predicts that masting will be unaffected by increasing mean temperatures under climate change; improves prediction of impacts on seed consumers; demonstrates that strongly masting species are hypersensitive to climate; explains the rarity of consecutive high-seed years without invoking resource constraints; and generates hypotheses about physiological mechanisms in plants and insect seed predators. For plants, ΔT has many attributes of an ideal cue. This temperature-difference model clarifies our understanding of mast seeding under environmental change, and could also be applied to other cues, such as rainfall.

Masting, the intermittent production of large flower or seed crops by a population of perennial plants, can enhance the reproductive success of participating plants and drive fluctuations in seed‐consumer populations and other ecosystem components over large geographic areas. The spatial and taxonomic extent over which masting is synchronized can determine its success in enhancing individual plant fitness as well as its ecosystem‐level effects, and it can indicate the types of proximal cues that enable reproductive synchrony. Here, we demonstrate high intra‐ and intergeneric synchrony in mast seeding by 17 species of New Zealand plants from four families across >150 000 km2. The synchronous species vary ecologically (pollination and dispersal modes) and are geographically widely separated, so intergeneric synchrony seems unlikely to be adaptive per se. Synchronous fruiting by these species was associated with anomalously high temperatures the summer before seedfall, a cue linked with the La Niña phase of El Niño–Southern Oscillation. The lone asynchronous species appears to respond to summer temperatures, but with a 2‐yr rather than 1‐yr time lag. The importance of temperature anomalies as cues for synchronized masting suggests that the timing and intensity of masting may be sensitive to global climate change, with widespread effects on taxonomically disparate plant and animal communities.

One of the longest continuing data sets involving a marine organism in the Antarctic is that of annual estimates of breeding population size of Adélie penguins Pygoscelis adeliae at colonies on Ross Island, Ross Sea, 1959 to 1997. The sizes of these colonies have displayed significant interannual variability during the 29-yr period. We hypothesized that changes are related to natural environmental factors; and used path analysis to analyze annual variation in population growth in relation to physical environmental factors during that part of the record with comparable sea-ice satellite imagery from 1973 to 1997. The Ross Sea sector of the Southern Ocean lying north of Ross Island, from 150°E to 130°W, comprised our study area. Annual population growth measured during summer was explained best, and inversely, by the extent of sea-ice in the study area 5 winters earlier, and in some way related to the Southern Oscillation. Analysis of a subset of the sea-ice data from 1979 to 1997 indicated strong correlations to ice conditions in the eastern portion of the study area (174 to 130°W), and virtually no correlations to the western half (150°E to 175°W). This result supported other indirect evidence that the Ross Island penguins winter in the eastern Ross Sea/western Amundsen Sea. A demographic model indicated that variation in survival of juveniles and subadults might account for the observed population variation, and would also explain the 5-yr lag as 5 yr is the average age of recruitment to the summer breeding population. Extensive sea-ice during winter appears to reduce subadult survival, expressed subsequently when these cohorts reach maturation. We hypothesize that extensive (more northerly) sea-ice limits access of penguins to productive waters known to occur south of the southern boundary of the Antarctic Circumpolar Current, with starvation or increased predation disproportionately affecting less-experienced birds. The observed patterns of penguin population change, including those preceding the satellite era, imply that sea-ice extent has changed significantly over recent decades.

In an investigation of the factors leading to geographic structuring among Adélie Penguin (Pygoscelis adeliae) populations, we studied the size and overlap of colony‐ specific foraging areas within an isolated cluster of colonies. The study area, in the southwestern Ross Sea, included one large and three smaller colonies, ranging in size from 3900 to 135 000 nesting pairs, clustered on Ross and Beaufort Islands. We used triangulation of radio signals from transmitters attached to breeding penguins to determine foraging locations and to define colony‐specific foraging areas during the chick‐provisioning period of four breeding seasons, 1997–2000. Colony populations (nesting pairs) were determined using aerial photography just after egg‐laying; reproductive success was estimated by comparing ground counts of chicks fledged to the number of breeding pairs apparent in aerial photos. Foraging‐trip duration, meal size, and adult body mass were estimated using RFID (radio frequency identification) tags and an automated reader and weighbridge. Chick growth was assessed by weekly weighing. We related the following variables to colony size: foraging distance, area, and duration; reproductive success; chick meal size and growth rate; and seasonal variation in adult body mass. We found that penguins foraged closest to their respective colonies, particularly at the smaller colonies. However, as the season progressed, foraging distance, duration, and area increased noticeably, especially at the largest colony. The foraging areas of the smaller colonies overlapped broadly, but very little foraging area overlap existed between the large colony and the smaller colonies, even though the foraging area of the large colony was well within range of the smaller colonies. Instead, the foraging areas of the smaller colonies shifted as that of the large colony grew. Colony size was not related to chick meal size, chick growth, or parental body mass. This differed from the year previous to the study, when foraging trips of the large colony were very long, parents lost mass, and chick meals were smaller. In light of existing data on prey abundance in neritic waters in Antarctica suggesting that krill are relatively evenly distributed and in high abundance in the Southern Ross Sea, we conclude that penguins depleted or changed the availability of their prey, that the degree of alteration was a function of colony size, and that the large colony affected the location (and perhaps ultimately the size) of foraging areas for the smaller colonies. It appears, therefore, that foraging dynamics play a role in the geographic structuring of colonies in this species.

No abstract

Abstract:Simultaneous, but contrary, decadal-scale changes in population trajectories of two penguin species in the western Pacific and Ross Sea sectors of the Southern Ocean, during the early/mid-1970s and again during 1988-89, correspond to changes in weather and sea ice patterns. These in turn are related to shifts in the semi-annual and Antarctic oscillations. Populations of the two ecologically dissimilar penguin species -Adélie Pygoscelis adeliae and emperor Aptenodytes forsteri -have been tallied annually since the 1950s making these the longest biological datasets for the Antarctic. Both species are obligates of sea ice and, therefore, allowing for the demographic lags inherent in the response of long-lived species to habitat or environmental variation, the proximate mechanisms responsible for the shifts involved changes in coastal wind strength and air and sea temperatures, which in turn affected the seasonal formation and decay of sea ice and polynyas. The latter probably affected such rates as the proportion of adults breeding and ultimately the reproductive output of populations in ways consistent with the two species' opposing sea ice needs. Corresponding patterns for the mid-1970s shift were reflected also in ice-obligate Weddell seal Leptonychotes weddelli populations and the structure of shallow-water sponge communities in the Ross Sea. The 1988-89 shift, by which time many more datasets had become available, was reflected among several ice-frequenting vertebrate species from all Southern Ocean sectors. Therefore, the patterns most clearly identified in the Pacific Sector were apparently spread throughout the high latitudes of the Southern Ocean.

In animal populations, a minority of individuals consistently achieves the highest breeding success and therefore contributes the most recruits to future generations. On average, foraging performance is important in determining breeding success at the population level, but evidence is scarce to show that more successful breeders (better breeders) forage differently than less successful ones (poorer breeders). To test this hypothesis, we used a 10-year, three-colony, individual-based longitudinal data set on breeding success and foraging parameters of a long-lived bird, the Adélie Penguin, Pygoscelis adeliae. Better breeders foraged more efficiently than poorer breeders under harsh environmental conditions and when offspring needs were higher, therefore gaining higher net energy profit to be allocated to reproduction and survival. These results imply that adverse "extrinsic" conditions might select breeding individuals on the basis of their foraging ability. Adélie Penguins show sufficient phenotypic plasticity that at least a portion of the population is capable of surviving and successfully reproducing despite extreme variability in their physical and biological environment, variability that is likely to be associated with climate change and, ultimately, with the species' evolution. This study is the first to demonstrate the importance of "extrinsic" conditions (in terms of environmental conditions and offspring needs) on the relationship between foraging behavior and individual quality.

Variation in annual flowering effort is described for 16 long datasets from 11 species of Chionochloa (Poaceae) in New Zealand. All populations exhibited extreme mast seeding. The most variable species was C. crassiuscula (coefficient of variation, CV= 3.02) over 26 years at Takahe Valley, Fiordland, which is the highest published CV we know of worldwide. The other populations also had high CVs (lowest CV= 1.42, mean CV = 1.84) which were higher than for other well-studied genera such as Picea, Pinus and Quercus. There were also frequent years of zero flowering (mean across all populations was 37.2% zero years; maximum 53% for C. rubra and C. crassiuscula over 19 years) whereas zero years are rare in other published masting datasets. Flowering was highly synchronous among species within a site (mean r= 0.886), and also (though significantly less so) among sites. Among sites, synchrony was not significantly higher within-species (mean r =0.711) than between-species (r= 0.690). Warm summer temperatures led to heavy flowering the following summer. Flowering synchrony increased with increasing synchrony in local deseasonalised summer temperatures, and decreased with increasing distance between sites. Mast seeding has been shown in Chionochloa to reduce losses to specialist flower or seed predators. Among-species synchrony may be adaptive if species share a common seed predator. Developing seeds of at least 10 Chionochloa species are attacked by larvae of an undescribed cecidomyiid. In Takahe Valley, where masting is most pronounced, cecidomyiids attacked all six Chionochloa species in all four years studied. Mean annual losses were almost constant (10.0 to 13.4%) while flowering effort varied 100-fold. The invariant losses are consistent with other evidence that the cecidomyiid may have extended diapause, which would make it harder to satiate by mast seeding. We hypothesise that one possible factor favouring such extremely high levels of mast seeding in Chionochloa is that its seed predator is very hard to satiate. Kelly and A. L. Harrison, Plant and Microbial Sciences, Uni6. of Canterbury, Christchurch 1, New Zealand (d.kelly@botn.canterbury.ac.nz). -W. G. Lee, Landcare Research, Pri6ate Bag 1930, Dunedin, New Zealand. -I. J. Payton, Landcare Research, P.O. Box 69, Lincoln, New Zealand. -P. R. Wilson, Landcare Research, Pri6ate Bag 6, Nelson, New Zealand. -E. M. Schauber, Dept of Ecology and E6olutionary Biology, Uni6. of Connecticut, Storrs, CT, USA and Inst. of Ecosystem Studies, Millbrook, NY, USA. Mast seeding is the intermittent synchronous production of large seed crops by a population of plants (Kelly 1994). It requires variation among years in the reproductive effort of individual plants and synchrony between individuals within a population. Mast seeding is found in plants from many different taxonomic groups and from most parts of the world, although it seems to be especially common in temperate forest trees (Silvertown 1980) and in the New Zealand flora (Webb and Kelly 1993, Kelly 1994). From an...