A long-term evaluation of fruiting phenology: importance of climate change

Abstract

Within the last decade the study of phenology has taken on new importance because of its contribution to climate-change research. However, phenology data sets spanning many years are rare in the tropics, making it difficult to evaluate possible responses of tropical communities to climate change. Here we use two data sets (1970-1983 and 1990-2002) to describe the fruiting patterns of the tropical tree community in Kibale National Park, Uganda. To address variation in spatial patterns, we describe fruiting over 2-3 y among four sites each separated by 12-15 km. Presently, the Kibale region is receiving c. 300 mm more rain than it did at the start of the century, droughts are less frequent, the onset of the rainy season is earlier, and the average maximum monthly temperature is 3.5 • C hotter than it was 25 y ago. The 1990-2002 phenology data illustrated high temporal variability in the proportion of the populations fruiting. Interannual variation in community-wide fruit availability was also high; however, the proportion of trees that fruited has increased over the past 12+ y. At the species level a variety of patterns were exhibited; however, a number of the most common species currently rarely fruit, and when they do, typically < 4% of the individuals take part in fruiting events. Combining the data set from 1990 to 2002 with that from 1970 to 1983 for specific species again reveals an increase in the proportion of trees fruiting between 1990 and 2002; however, the proportion of the populations fruiting decreased during the earlier period. When one examines particular species over this whole period a variety of patterns are evident. For example, Pouteria altissima exhibited a relatively regular pattern of fruiting during the 1970s; however, it rarely fruited in the 1990s. Contrasting phenological patterns at four sites revealed that at the community level the fruiting patterns of only one of the six pair-wise site combinations were correlated. Relationships between rainfall and fruiting were variable among sites. Contrasting changes in fruiting patterns over the 30 y with differences among the four sites varying in rainfall, suggests that the changes observed in fruiting may be due to climate change. Responses to this climate change are likely complex and will vary among species. However, for some species, current conditions appear unsuitable for fruiting.

Wild chimpanzees plan their breakfast time, type, and location

“…We propose that large-brained foragers that need a reliable and steady intake of high-energy nutrition to maintain their large and costly brains (6,11) could gain a clear evolutionary advantage by using flexible planning that reduces indirect interspecific competition. This attribute may have been particularly important for hominoids that specialized on stationary, energy-rich, and highly ephemeral food, such as ripe fruit (14,17,24), abandoned meat carcasses, or aquatic fauna trapped in receding waters (56). The proposed benefit of flexible planning skills, especially for hominids living in highly seasonal habitats like savannah, strongly encourages a more detailed focus on the temporal aspect of ecological complexity than has been done to date (1,6), and a resumed investigation of its role in theories of primate and, in particular, hominid brain size evolution (11).…”

“…14 and 15). Despite the persistent illusion of abundance created by giant fruit trees and lush foliage, ripe-fruit specialists in particular can face severe food shortages, such as for months, when only 0.2% of the trees carry ripe fruit (14,15). The availability of nutritious rainforest food, like young leaves and ripe fruit, can be highly episodic and patchily distributed in time and space and very ephemeral in terms of optimal nutritional quality (e.g., refs.…”

Phenology of tropical understory trees: patterns and correlates

“…To better understand the degree to which climate and species interactions affect phenological patterns of tropical plants, studies in other tropical forests will be required, ideally spanning several years (Newstrom et al 1992, Chapman et al 2005. A full understanding of tropical phenologies is made difficult by the fact that measurements must be made frequently during the entire year.…”

Patterns of litter production in a secondary alluvial Atlantic Rain Forest in southern Brazil

“…Spearman's rank correlation coeffi cients (r s ) were calculated according to Zar (1999) to correlate litter components produced along the months (considering the mean of the two sites due to the similar behavior and to simplify the results) with meteorological variables. Similar non-parametric correlations are also used in many phenological and litterfall studies , Marques & Oliveira 2004, Chapman et al 2005.…”

“…Many phenological and litterfall studies used correlations to detect synchronies among biological and meteorological cycles, without the pretension of explaining relations of cause and effect through these analyses , Marques & Oliveira 2004, Chapman et al 2005. According to Morellato et al (2000) those relationships remain ambiguous for tropical forests under less and non-seasonal climates where even simple patterns of fl owering, fruiting or formation of new leaves are hardly understood, much less the interaction of these patterns with successional dynamics.…”