Robert O. Lawton

Climatic Impact of Tropical Lowland Deforestation on Nearby Montane Cloud Forests

Tropical montane cloud forests (TMCFs) depend on predictable, frequent, and prolonged immersion in cloud. Clearing upwind lowland forest alters surface energy budgets in ways that influence dry season cloud fields and thus the TMCF environment. Landsat and Geostationary Operational Environmental Satellite imagery show that deforested areas of Costa Ricas Caribbean lowlands remain relatively cloud-free when forested regions have well-developed dry season cumulus cloud fields. Further, regional atmospheric simulations show that cloud base heights are higher over pasture than over tropical forest areas under reasonable dry season conditions. These results suggest that land use in tropical lowlands has serious impacts on ecosystems in adjacent mountains.

HETEROCHRONY,DEFERRED BREEDING, AND AVIAN SOCIALITY

After a century’s fall from theoretical grace, the relationship between ontogeny and phylogeny has once again become a topic of intense evolutionary interest (cf. Gould, 1977; Nelson, 1978). The focus of the renaissance is the phenomenon of heterochrony. A complex concept, heterochrony refers to changes in the timing of ontogeny, specifically to shifts in development of one organ system with respect to other systems (Gould, 1977).

HOST PREFERENCES OF RHUS RADICANS (ANACARDIACEAE) IN A SOUTHERN DECIDUOUS HARDWOOD FOREST

Rhus radicans, a root-climbing liana, is not distributed randomly among potential host tree species in an old-growth mixed mesophytic forest on the southern Cum- berland Plateau of north Alabama, USA. Vines are more abundant than expected on Carya ovata and Quercus rubra, but less abundant than expected on Juglans nigra, Acer sac- charum, and Sassafras albidum. Seed germination and early seedling growth in the presence of bark extracts suggest allelochemical interactions may influence the observed host pref- erences.

A Phytochemical investigation of Alchornea latifolia

A phytochemical investigation of the chloroform leaf extract of Alchornea latifolia has been undertaken. Along with the triterpenoids taraxerone, friedelin, epifriedelinol, and taraxerol, the plant also contains seco-3,4-friedelin (dihydroputranjivic acid) (1) and seco-3,4-taraxerone (2). These A-ring-opened triterpenoids show in vitro cytotoxic activity against Hep-G2 and A-431 human cancer cell lines and are potent inhibitors of topoisomerase II.

The breeding biology of the brown jay in Monteverde, Costa Rica

-In an expanding population of Brown Jays (Cyanocorax morio) in the Cordillera de Tilaran of Costa Rica, flocks exhibit a broad range of breeding behavior involving the construction of one or more nests by two or more birds, egg-laying, incubation and brooding at one nest by one or more females, and nestling care by breeding and non-breeding birds. The form that breeding behavior takes may be related to the ages of flock members. Flocks vary considerably in age, and breeding success is correlated with the number of older birds. The variation in Brown Jay breeding behavior may provide some insight into the evolution of social organization in New World corvids. Several authors have suggested that habitat change or release from saturation may induce enormous changes in social structure and behavior of cooperatively breeding birds (Brown and Balda 1977; Vehrencamp 1978; Stacey 1978, 1979a, b; Reyer 1980; Hardy et al. 1981). The most compelling arguments in favor of this hypothesis, however, have resulted from comparative studies of separate populations either in different environments (Cox, unpubl.; Stacey 1978, 1979a, b; Reyer 1980; Koenig 1981) or in populations where habitat quality varied conspicuously (at least to human eyes) over a small geographic area (Brown and Balda 1977, Vehrencamp 1978, Hardy et al. 1981). To date, information on the demographic and behavioral effects of change in saturation within one population has been unavailable, in part because many researchers consider gross population manipulation (i.e., removing a significant portion of a population or destroying habitat) unethical. Moreover, because the study of complex social behavior necessitates longterm investigation, most field workers seek study populations in the protected environments of nature preserves. As a result, their study populations frequently exist under saturated conditions and do not fluctuate much from year to year. One way to investigate the effects of saturation on social organization and behavior, however, is to study natural experiments by identifying and investigating populations that have recently been released from, or are rapidly approaching saturation. For instance, in 1978, one of the worlds best studied populations of cooperative breeders (Woolfenden and Fitzpatrick 1984)-Florida Scrub Jays (Aphelocoma coerulescens) on the Archbold Biological Station in Florida-was decimated, probably by an epidemic (J. Fitzpatrick, pers. comm.). Because of the wealth of base line information available for this population, documenting changes in behavior and social organization as the population recovers represents an ideal natural experiment. In this paper, we present the results of a twoyear study of Brown Jays (Cyanocorax morio) in a population whose dynamics may also represent the naturally occurring experimental conditions necessary to test current notions of the relationship between habitat saturation and sociobiology. We designed a study to address a series of a priori hypotheses concerning the role of helpers at the nest (Lawton and Lawton 1980, Lawton and Guindon 1981, Lawton and Lawton, unpubl.). In the course of our work, we discovered that Brown Jay flocks in Monteverde are extraordinarily heterogeneous with respect to age-class composition. We think this heterogeneity may be attributed to the fact that the population is still expanding after original colonization about thirty years ago (W. Guindon, pers. comm.), shortly after the highland plateau of Monteverde was cleared for dairy farming. Although Monteverde has experienced no significant clearing since our study began, the number ofjays in our study area has increased twenty percent (Lawton, Lawton, Lewis, and Lowther, unpubl.). Population growth is not simply the result of increased flock size, but derives from an increased number of flocks in the study area (1978: n = 14; 1982: n = 16). Growth is also reflected by expansion into new habitat. Of two flocks formed since 1978, one has become established in the highest clearing in Monteverde, an area abutting a natural species border: the large, uninterrupted expanse of cloud forest.

Population growth, range expansion, and competition in the cooperatively breeding brown jay, Cyanocorax morio

Abstract Abstract. Observations of an expanding population of brown jays in Monteverde, Costa Rica made it possible to characterize a transition from incomplete habitat saturation, in which jays maintained moderate group sizes, to more complete habitat saturation, in which jays maintained larger group sizes and showed increased aggression at high densities. From 1977 to 1990, the number of individuals, number of flocks, and mean flock size on the study area increased dramatically. Only at high densities did flocks comprised of fewer than six individuals attempt breeding, even though suitable habitat (indicated by later successful breeding there), had been available for the past decade. The population has expanded its local range as well, and now occupies all of the preferred cleared habitat in the study area. Coincident with these demographic changes, the emergence of overt intra-group aggression at the nest was observed, especially that involving interference competition between rival older females during the building/laying stage of the nesting cycle. Aggressive interactions at a nest were much more likely in flocks with more than 10 individuals and also more likely as the number of birds seen sitting on the nest increased. The positive relationship between number of offspring produced and the number of old birds in a flock was weakened at higher densities, probably resulting from increased intra-group aggression. These observations suggest that high population density and limited breeding opportunities resulted in increased reproductive competition. Sociality, however, has not simply been forced in this population, because even at low densities in the presence of ample unused habitat Monteverde brown jays bred only in groups. This suggests that intrinsic benefits to group living probably have also played an important part in maintaining sociality in this population.

Biogeography of tropical montane cloud forests. Part II: Mapping of orographic cloud immersion

Abstract This study details two unique methods to quantify cloud-immersion statistics for tropical montane cloud forests (TMCFs). The first technique uses a new algorithm for determining cloud-base height using Moderate Resolution Imaging Spectroradiometer (MODIS) cloud products, and the second method uses numerical atmospheric simulation along with geostationary satellite data. Cloud-immersion statistics are determined using MODIS data for March 2003 over the study region consisting of Costa Rica, southern Nicaragua, and northern Panama. Comparison with known locations of cloud forests in northern Costa Rica shows that the MODIS-derived cloud-immersion maps successfully identify known cloud-forest locations in the United Nations Environment Programme (UNEP) World Conservation Monitoring Centre (WCMC) database. Large connected regions of cloud immersion are observed in regions in which the trade wind flow is directly impinging upon the mountain slopes; in areas in which the flow is parallel to the slopes,...

Leaf essential oil composition of five Zanthoxylum species from Monteverde, Costa Rica

The leaf essential oils from five species of Zanthoxylum (Rutaceae) from Monteverde, Costa Rica, have been obtained by hydrodistillation and analyzed by gas chromatography-mass spectrometry. The species examined include Z. fagara, Z. acuminatum, Z. melanostictum, Z. monophyllum, and an undescribed species. The most abundant classes of compounds found in Zanthoxylum leaf oils are acyclic and menthane monoterpenoids as well as simple alcohols, aldehydes, and ketones. In terms of molecular diversity, menthane and acyclic monoterpenoids, cadinane and mesocyclic sesquiterpenoids, and simple alcohols, aldehydes, and ketones dominate the essential oils of Zanthoxylum species. Monoterpenoids make up the majority of the mass of the leaf oils of Z. monophyllum, Z. acuminatum, Z. fagara, and Zanthoxylum sp. nov. Linalool, 4-terpineol, α-terpineol, and trans-2-hexenol, are found in all of the Zanthoxylum species examined in this study.

Quantitative Measures of Immersion in Cloud and the Biogeography of Cloud Forests

Sites described as tropical montane cloud forests differ greatly, in part because observers tend to differ in their opinion as to what constitutes frequent and prolonged immersion in cloud. This definitional difficulty interferes with hydrologic analyses, assessments of environmental impacts on ecosystems, and biogeographical analyses of cloud forest communities and species. Quantitative measurements of cloud immersion can be obtained on site, but the observations are necessarily spatially limited, although well-placed observers can examine 10 50 km of a mountain range under rainless conditions. Regional analyses, however, require observations at a broader scale. This chapter discusses remote sensing and modeling approaches that can provide quantitative measures of the spatiotemporal patterns of cloud cover and cloud immersion in tropical mountain ranges. These approaches integrate remote sensing tools of various spatial resolutions and frequencies of observation, digital elevation models, regional atmospheric models, and ground-based observations to provide measures of cloud cover, cloud base height, and the intersection of cloud and terrain. This combined approach was applied to the Monteverde region of northern Costa Rica to illustrate how the proportion of time the forest is immersed in cloud may vary spatially and temporally. The observed spatial variation was largely due to patterns of airflow over the mountains. The temporal variation reflected the diurnal rise and fall of the orographic cloud base, which was influenced in turn by synoptic weather conditions, the seasonal movement of the Intertropical Convergence Zone and the north-easterly trade winds. Knowledge of the proportion of the time that sites are immersed in clouds should facilitate ecological comparisons and biogeographical analyses, as well as land use planning and hydrologic assessments in areas where intensive on-site work is not feasible.

Importance of land use versus atmospheric information verified from cloud simulations from a frontier region in Costa Rica

[1] Land-use/land-cover (LULC) change has been recognized as a key component in global climate change, and numerous climate modeling studies at regional to global scales document this. The research strategies have invariably been to first conduct baseline simulations of current conditions to evaluate model performance. Then simulation of regional climate with land cover changes (LCC) implemented within the model allows differences with the baseline simulation to be used as evidence of global to regional-scale climate impacts of LCC. However, even state-of-the-art regional climate models require two data sets to conduct reasonable baseline simulations. These are representative current land cover and atmospheric information over the study region. In frontier and developing areas (where most of the rapid land-use conversion is taking place), these data sets are frequently unavailable and the errors in simulations are due to either inaccurate land cover, insufficient atmospheric information, nonrepresentative model physics, or a combination of one or more of the above. This study shows that in one frontier region, that surrounding the Cordillera de Tilaran of Costa Rica, the accuracy of simulating clouds decreases by 1% to 3% if default model land cover information is used. If the atmospheric data sets used are the ones usually available to researchers (with land cover information held constant), then the model accuracy is reduced by 21% to 25%. Model runs without updated land cover or atmospheric information reduce model accuracy slightly further. Precipitation comparisons also provide similar results. This study thus shows that the critically important data set for conducting accurate simulations is not land cover information but atmospheric information. Researchers may similarly get significant increase in the accuracy of their baseline simulations elsewhere by using radiosondes/rawinsondes over their study region. Finally, since atmospheric information is not available for different landscape scenarios, assessments of the relative role of LULC change will have to continue to rely on using the standard atmospheric data set and the acceptance that the use of more detailed atmospheric data to initialize and provide lateral boundary conditions would have reduced the uncertainties in such landscape sensitivity studies.