Collaborative Use of Sensor Networks and Cyberinfrastructure to Understand Complex Ecosystem Interactions in a Tropical Rainforest: Challenges and Lessons Learned.

Collaborations between ecosystem ecologists and engineers have led to impressive progress in developing complex models of biogeochemical fluxes in response to global climate change. Ecology and engineering iteratively inform and transform each other in these efforts. Nested data streams from local sources, adjacent networks, and remote sensing sources together magnify the capacity of ecosystem ecologists to observe systems in near real-time and address questions at temporal and spatial scales that were previously unobtainable. We describe our research experiences working in a Costa Rican rainforest ecosystem with the challenges presented by constant high humidity, 4300 mm of annual rainfall, flooding, small invertebrates entering the tiniest openings, stinging insects, and venomous snakes. Over the past two decades, we faced multiple challenges and learned from our mistakes to develop a broad program of ecosystem research at multiple levels of integration. This program involved integrated networks of diverse sensors on a series of canopy towers linked to multiple belowground soil sensor arrays that could transport sensor data streams from the forest directly to an off-site location via a fiber optic cable. In our commentary, we highlight three components of our work: (1) the eddy flux measurements using canopy towers; (2) the soil sensor arrays for measuring the spatial and temporal patterns of CO2 and O2 fluxes at the soil-atmosphere interface; and (3) focused investigations of the ecosystem impact of leaf-cutter ants as "ecosystem engineers" on carbon fluxes.

Invasive annuals respond more negatively to drought than native species.

In his foundational list of 'ideal weed' characteristics, Baker (1965) proposed that weedy plants maximize reproductive output under high resource availability. Since then, the idea that invasive plant species are more responsive to fluctuating resources compared with native or noninvasive species has gained considerable traction, although few studies extend this hypothesis to include reproductive output. We revisit Baker's hypothesis in the context of invasion and drought in California grasslands, exploring whether invasives show greater growth and reproductive responses to water availability compared with the native wildflowers they displace. In an outdoor potted study, we grew eight native and eight invasive species of annuals commonly found in southern California grasslands to reproductive maturity under both well-watered and drought conditions. While drought negatively impacted plant performance overall, invasives showed more negative responses for growth and reproductive traits. Invasives also grew larger than native species, especially under well-watered conditions, and produced seed with higher rates of germination. Invasives may be more negatively impacted by drought compared with natives, but they are also able to capitalize on high resource conditions and greatly increase reproductive output. Such opportunistic responses exhibited by invasives might explain previously observed fluctuations in their abundance under variable precipitation.

Phenotypic plasticity and differentiation in fitness-related traits in invasive populations of the Mediterranean forb Centaurea melitensis (Asteraceae).

PREMISE OF THE STUDY: Biological invasions threaten global biodiversity, resulting in severe ecological and economic costs. Phenotypic plasticity and differentiation in fitness-related traits after introduction can contribute to increased performance in invasive populations of plants. We determined whether postintroduction evolution in trait means or in their plasticity, or inherent species-wide phenotypic plasticity has promoted invasiveness in a European annual forb. • METHODS: In a common greenhouse, we compared several fitness-related traits and the phenotypic plasticity of those traits under four levels of nutrients among native and invasive populations of Centaurea melitensis. We tested 18 populations from three regions of similar mediterranean climate type: the native range (southern Spain) and two invaded ranges (California and central Chile). • KEY RESULTS: Centaurea melitensis possesses overall phenotypic plasticity, which is a trait that promotes invasiveness. Invasive populations were differentiated from native plants for several trait means and their levels of phenotypic plasticity in directions that enhance competitive ability and success. Invasive plants flowered earlier and grew faster in the early stages of growth phases, important features for invasiveness. • CONCLUSIONS: Phenotypic plasticity, its evolution postinvasion, and the evolution of fitness-related trait means in invasive populations have potentially contributed to the invasion of C. melitensis in California and Chile. Along with an overall wide range of tolerance to growing conditions, C. meltiensis populations that have colonized habitats in California and Chile have undergone rapid evolution in several life history traits and the plasticities of those traits in directions that would promote invasiveness in mediterranean ecosystems.

Functional trait diversity of Cyclanthaceae and its convergent evolution with Araceae in Neotropical forests.

The Cyclanthaceae comprise a relatively small family of about 230 species and 12 genera in the Pandanales that is widespread in wet Neotropical forests. The great majority of species can be divided into three growth forms (understory herbs, epiphytes, and root-climbing hemiepiphytes) that share functional traits with similar growth forms present in the Araceae, a member of the Alismatales and not closely related. Our objectives were first to characterize the diversity, functional growth forms, and ecological traits of Cyclanthaceae at the La Selva Biological Station. Specific functional leaf and canopy traits of terrestrial herbs and epiphytes are very similar and associated with ecological success in both families. We further examined the functional traits of root-climbing hemiepiphytes, a specialized growth form that links the two families but rare in other families and argue that their specialized functional traits allow them to be considered as a distinct functional growth form. A key trait in distinguishing hemiepiphytes which are rare outside of the Cyclanthaceae and Araceae is the severance of the main stem hydraulic connection to the soil early in plant development. We used field data to examine the possible evolutionary pathways of developmental and ecological transition from terrestrial to hemiepiphyte growth forms. The broader ecological success of hemiepiphytic Araceae compared to Cyclanthaceae is hypothesized to result from the presence of heteroblasty in developing stems and leaves which allows more efficient utilization of complex canopy light environments of wet tropical forests.

Differential Species Richness and Ecological Success of Epiphytes and Hemiepiphytes of Neotropical Araceae and Cyclanthaceae.

Numerous plant functional traits of ecophysiology and morphology associated with an epiphytic life history have promoted relatively high rates of evolutionary diversification and ecological success in tropical families such as the Orchidaeae, Polypodiaceae, Bromeliaceae, and Cactaceae. Epiphytic life histories are relatively uncommon in the Araceae and rare in the Cyclanthaceae which lack key functional traits for epiphytism. Only two lineages of Neotropical Araceae, Anthurium and Philodendron, include examples of epiphyte life histories. The evolution of a hemiepiphytic life history represented an important development for tropical Araceae by providing functional traits that have greatly expanded opportunities for adaptive radiation and ecological success as indicated by species richness and frequency of occurrence. The key adaptive trait allowing the diversification of hemiepiphytic Araceae was the development of heteroblastic growth of leaves and stems. Although hemiepiphytic life histories are present in the Cyclanthaceae, the family has undergone only modest speciation and limited ecological success in both its epiphytes and hemiepiphytes. Extensive sampling of more than 4600 trees from primary forest on four soil groups in northeastern Costa Rica have found a modest diversity of 15 species of epiphytic Araceae but only two species of epiphytic Cyclanthaceae. In contrast, 38 species of hemiepiphytic Araceae and 5 species of hemiepiphytic Cyclanthaceae were sampled, indicating relatively limited adaptive radiation of hemiepiphytic Cyclanthaceae and lower ecological success. Using summed values of frequency of occurrence as a measure of ecological success, epiphytic Araceae were 18 to 42 times more frequent than epiphytic Cyclanthaceae in swamp, alluvial, and residual soil forests. Summed frequencies of occurrence of hemiepiphytic Araceae were 7 to 13 times higher than those of hemiepiphytic Cyclanthaceae. The four soil groups were similar in their floristic composition of epiphytic and hemiepiphytic Araceae and Cyclanthaceae, but the frequencies of occurrence of both epiphytes and hemiepiphytes were, with few exceptions, highest on swamp soil plots, with alluvial soil plots slightly less favorable.

Leaf-cutter ants - mycorrhizal fungi: observations and research questions from an unexpected mutualism.

Leaf-cutter ants (LCAs) are widely distributed and alter the physical and biotic architecture above and below ground. In neotropical rainforests, they create aboveground and belowground disturbance gaps that facilitate oxygen and carbon dioxide exchange. Within the hyperdiverse neotropical rainforests, arbuscular mycorrhizal (AM) fungi occupy nearly all of the forest floor. Nearly every cubic centimeter of soil contains a network of hyphae of Glomeromycotina, fungi that form arbuscular mycorrhizae. Our broad question is as follows: how can alternative mycorrhizae, which are-especially ectomycorrhizae-essential for the survival of some plant species, become established? Specifically, is there an ant-mycorrhizal fungus interaction that facilitates their establishment in these hyperdiverse ecosystems? In one lowland Costa Rican rainforest, nests of the LCA Atta cephalotes cover approximately 1.2% of the land surface that is broadly scattered throughout the forest. On sequencing the DNA from soil organisms, we found the inocula of many AM fungi in their nests, but the nests also contained the inocula of ectomycorrhizal, orchid mycorrhizal, and ericoid mycorrhizal fungi, including Scleroderma sinnamariense, a fungus critical to Gnetum leyboldii, an obligate ectomycorrhizal plant. When the nests were abandoned, new root growth into the nest offered opportunities for new mycorrhizal associations to develop. Thus, the patches created by LCAs appear to be crucial sites for the establishment and survival of shifting mycorrhizal plant-fungal associations, in turn facilitating the high diversity of these communities. A better understanding of the interactions of organisms, including cross-kingdom and ant-mycorrhizal fungal interactions, would improve our understanding of how these ecosystems might tolerate environmental change.

Plasticity in Compensatory Growth to Artificial Defoliation and Light Availability in Four Neotropical Understory and Forest Edge Herb Species.

Defoliation from falling branches is a major factor in the survival of understory herbs in tropical rainforests. Experimental studies of defoliation under three levels of light environment compared responses to partial and total defoliation in four species of tropical rainforest understory herbs. We predicted that elevated levels of light availability would help compensate for damage to through compensatory growth in both understory and forest edge species and that forest edge species would more effectively compensate under high light conditions than shade-tolerant species from the forest understory All species showed a high tolerance to defoliation under high and intermediate light conditions. Under low-light conditions survival differed dramatically with minimal mortality in forest-edge species compared to high mortality in completely defoliated understory species. Defoliation, and light × defoliation interactions, impacted multiple growth traits in understory species. In contrast, forest-edge species showed no effect of defoliation except on total biomass, and only one light × defoliation interaction was observed. Our results indicate that differences in biomass allocation, leaf ecophysiology, and other growth parameters between forest understory and edge species may be structuring post-damage response in understory and forest edge herbs.

Functional traits of broad-leaved monocot herbs in the understory and forest edges of a Costa Rican rainforest.

Broad-leaved monocot herbs are widespread and dominant components of the shaded understories of wet neotropical forests. These understory habitats are characterized by light limitation and a constant threat of falling branches. Many shaded understory herb species have close relatives that occupy forest edges and gaps, where light availability is higher and defoliation threat is lower, creating an opportunity for comparative analysis of functional traits in order to better understand the evolutionary adaptations associated with this habitat transition. We documented ecological, morphological and ecophysiological traits of multiple herb species in six monocot families from each of these two habitats in the wet tropical rainforest at the La Selva Biological Station, Costa Rica. We found that a mixture of phylogenetic canalization and ecological selection for specific habitats helped explain patterns of functional traits. Understory herbs were significantly shorter and had smaller leaves than forest edge species. Although the mean number of leaves per plant and specific leaf area did not differ between the two groups, the larger leaf size of forest edge species gave them more than three times the mean plant leaf area. Measures of leaf water content and nitrogen content varied within both groups and mean values were not significantly different. Despite the high leaf nitrogen contents, the maximum photosynthetic rates of understory herbs were quite low. Measures of δ 13C as an analog of water use efficiency found significantly lower (more negative) values in understory herbs compared to forest edge species. Clonality was strongly developed in several species but did not show strong phylogenetic patterns. This study highlights many functional traits that differ between broad-leaved monocot species characteristic of understory and forest edge habitats, as well as traits that vary primarily by phylogenetic relatedness. Overall, plant functional traits do not provide a simple explanation for the relative differences in abundance for individual understory and forest edge species with some occurring in great abundance while others are relatively rare.

Environmental sensor networks in ecological research.

Environmental sensor networks offer a powerful combination of distributed sensing capacity, real-time data visualization and analysis, and integration with adjacent networks and remote sensing data streams. These advances have become a reality as a combined result of the continuing miniaturization of electronics, the availability of large data storage and computational capacity, and the pervasive connectivity of the Internet. Environmental sensor networks have been established and large new networks are planned for monitoring multiple habitats at many different scales. Projects range in spatial scale from continental systems designed to measure global change and environmental stability to those involved with the monitoring of only a few meters of forest edge in fragmented landscapes. Temporal measurements have ranged from the evaluation of sunfleck dynamics at scales of seconds, to daily CO2 fluxes, to decadal shifts in temperatures. Above-ground sensor systems are partnered with subsurface soil measurement networks for physical and biological activity, together with aquatic and riparian sensor networks to measure groundwater fluxes and nutrient dynamics. More recently, complex sensors, such as networked digital cameras and microphones, as well as newly emerging sensors, are being integrated into sensor networks for hierarchical methods of sensing that promise a further understanding of our ecological systems by revealing previously unobservable phenomena.

Fire and Plant Diversification in Mediterranean-Climate Regions.

Despite decades of broad interest in global patterns of biodiversity, little attention has been given to understanding the remarkable levels of plant diversity present in the world's five Mediterranean-type climate (MTC) regions, all of which are considered to be biodiversity hotspots. Comprising the Mediterranean Basin, California, central Chile, the Cape Region of South Africa, and southwestern Australia, these regions share the unusual climatic regime of mild wet winters and warm dry summers. Despite their small extent, covering only about 2.2% of world land area, these regions are home to approximately one-sixth of the world vascular plant flora. The onset of MTCs in the middle Miocene brought summer drought, a novel climatic condition, but also a regime of recurrent fire. Fire has been a significant agent of selection in assembling the modern floras of four of the five MTC regions, with central Chile an exception following the uplift of the Andes in the middle Miocene. Selection for persistence in a fire-prone environment as a key causal factor for species diversification in MTC regions has been under-appreciated or ignored. Mechanisms for fire-driven speciation are diverse and may include both directional (novel traits) and stabilizing selection (retained traits) for appropriate morphological and life-history traits. Both museum and nursery hypotheses have important relevance in explaining the extant species richness of the MTC floras, with fire as a strong stimulant for diversification in a manner distinct from other temperate floras. Spatial and temporal niche separation across topographic, climatic and edaphic gradients has occurred in all five regions. The Mediterranean Basin, California, and central Chile are seen as nurseries for strong but not spectacular rates of Neogene diversification, while the older landscapes of southwestern Australia and the Cape Region show significant components of both Paleogene and younger Neogene speciation in their diversity. Low rates of extinction suggesting a long association with fire more than high rates of speciation have been key to the extant levels of species richness.

Size class structure, growth rates, and orientation of the central Andean cushion Azorella compacta.

Azorella compacta (llareta; Apiaceae) forms dense, woody, cushions and characterizes the high elevation rocky slopes of the central Andean Altiplano. Field studies of an elevational gradient of A. compacta within Lauca National Park in northern Chile found a reverse J-shape distribution of size classes of individuals with abundant small plants at all elevations. A new elevational limit for A. compacta was established at 5,250 m. A series of cushions marked 14 years earlier showed either slight shrinkage or small degrees of growth up to 2.2 cm yr(-1). Despite their irregularity in growth, cushions of A. compacta show a strong orientation, centered on a north-facing aspect and angle of about 20° from horizontal. This exposure to maximize solar irradiance closely matches previous observations of a population favoring north-facing slopes at a similar angle. Populations of A. compacta appear to be stable, or even expanding, with young plants abundant.

Nitrogen utilization efficiencies in mediterranean-climate shrubs of California and Chile.

Comparative studies of nitrogen utilization efficiencies (g assimilation mg-1 leaf nitrogen expended) for dominant chaparral shrubs of California and matorral shrubs of central Chile indicate varying relationships of these efficiencies to total shrub productivity and community dominance. In California where nitrogen is limiting for shrub growth, increasing nitrogen utilization efficiency is correlated with increased productivity, and species with the highest values are dominant on polar (north-facing) slopes. In Chile where soil nutrients are not strongly limiting, increased nitrogen utilization efficiency beyond a low threshold has little or no effect on productivity. This may be an important aspect of the relative ecological success of deciduous shrubs in Chile. High nitrogen utilization efficiency in Chile is associated with broad ecological amplitude rather than increased competitive ability through higher productivity.

The ecological distribution of C4 and C3 grasses in the Hawaiian Islands.

Nearly two-thirds of both the native and exotic grasses of the Hawaiian Islands are C4 species. Elevational gradients on the island of Hawaii demonstrate that C4 taxa dominate both species composition and coverage of grasses up to 1,000 m, while C3 taxa predominate above 1,400 m. The elevational transition of dominance between the two metabolic systems is much sharper on a coverage than on a floristic composition basis. Despite the shaded characteristic of the habitat, C4 grasses are the most important group in wet forests at intermediate elevations. The 1,400 m elevation of floristic balance between C4 and C3 grasses corresponds to a low monthly mean minimum temperature of approximately 9° C and a mean maximum temperature for the warmest month of about 21° C. These temperatures are considerably lower than those reported for a latitudinal point of floristic balance in North America, but similar to those indicated by other studies of elevational distributions of tropical grasses.

Sexual dimorphism and resource allocation in male and female shrubs of Simmondsia chinensis.

Desert populations of the evergreen dioecious shrub Simmondsia chinensis exhibit sex-related leaf and canopy dimorphisms not present in populations from more mesic coastal environments. Leaves on female shrubs have characteristically larger sizes, greater specific weights, and greater water-holding capacity than male leaves in desert habitats. In coastal scrub environments no significant difference is present, with leaf characteristics of both sexes similar to those of desert male shrubs. Desert female shrub canopies are typically relatively open with little mutual branch shading. In male shrubs canopies are more densely branched with considerable mutual shading of branches. Female plants allocate a greater proportion of their vegetative resources to leaves than do male plants. Considering total biomass, male plants allocate 10-15% of their resources (biomass, calories, glucose-equivalents, nitrogen, phosphorus) to reproductive tissues. Female allocation is dependent on seed set. At 100% seed set females would allocate 30-40% of their resources to reproduction, while female reproductive investment would equal that of males at approximately 30% seed set. Sexual dimorphism and the associated physiological characteristics in Simmondsia act as an alternative to differential habitat selection by male and female plants. Female plants respond to limited water resources in desert areas by increasing their efficiency in allocating limited resources to reproductive structures.

Morphological adaptations of tracheid structure to water stress gradients in the crown of Sequoiadendron giganteum.

Mean radial diameter of tracheids in young branches of a 90 m Sequoiadendron giganteum decreases linearly with height along a gradient correlated linearly with decreasing xylem pressure potential. These smaller tracheid diameters provide strength to resist strong mechanical tensions in the xylem column and hypothetically allow greater efficiencies of water conduction. Tracheid length is not significantly correlated with either water stress or tracheid diameter.

The role of fire as a mineralizing agent in a Sierran coniferous forest.

The role of fire as an agent for mineralizing forest floor organic matter was investigated in a Sierra Nevada sequoia-mixed conifer forest. Soil chemical properties were determined in a series of small paired plots on and adjacent to burns done by the National Park Service in their control burn program. Total nitrogen, carbon, and cation exchange capacity were found to be significantly lower on burned plots, and phosphorus, calcium, magnesium, potassium, and pH were significantly higher on burned plots. The seasonal course of certain soil chemical properties was determined in a single set of larger plots. Total nitrogen, nitrate, ammonium, phophorus, and pH were shown to increase in the spring. It is concluded that fire is an effective but not a conservative mineralizing agent.

Carbon isotope ratios of central Mexican Crassulaceae in natural and greenhouse environments.

Measurements of carbon isotope ratios of central Mexican Crassulaceae collected over a broad habitat range show consistent patterns of CAM activity with no indications of substantial flexible photosynthetic pathways between C3 and CAM. The three genera studied - Echeveria, Pachyphytum, and Graptopetalum - are all closely related to Dudleya in which considerable flexible metabolic response has been demonstrated. Comparative measurements of carbon isotope ratios for field collected and greenhouse reared samples of the same taxa showed a uniform occurrence of slightly more negative δ 13C values, but no indication of substantial flexible metabolic response.

Carbon and hydrogen isotope ratios of bryophytes from arid and humid regions.

Measurements of carbon isotope ratios of nine taxa of arid zone mosses from North America and 24 taxa of European bryophytes show consistent values indicative of C3 metabolism. Other morphological, physiological and biochemical characteristics provide the mechanism of adaptation to environmental stresses of heat and extended desiccation in these plants. Analyses of D content indicate that values become less negative with increasing aridity of the habitat.

Parallel evolution of leaf pubescence in Encelia in coastal deserts of North and South America.

Members of the shrub genus Encelia occur in the arid coastal regions of western North America and South America along gradients of precipitation extending from less than 50 mm annually to somewhat over 350 mm. At moist ends of the gradient species possess glabrate, green leaves. Proceeding to drier regions, the species possess progressively more pubescent, whiter leaves. Leaf absorptance to solar radiation decreases with precipitation in an identical pattern along gradients in both North and South America.

Summer water relations of the desert phreatophyte Prosopis glandulosa in the Sonoran Desert of southern California.

Prosopis is a genus of phreatophytic trees inhabiting hot deserts and semiarid grasslands of the world. Although desert trees are exposed to unusual environmental temperature and water stress, few investigations have evaluated their water relations. This is particularly true for Prosopis species growing in areas where a large portion of their water use comes from ground water.Water relations components for Prosopis glandulosa were studied at Harper's Well, near the Salton Sea, California during the summer months of 1980. Maximum temperatures (49° C), irradiance (2,000 µE/m2/sec), and vapor pressure deficit (5.3 kPa) were reached in July. During this time Prosopis glandulosa predawn xylem pressure potentials were below-3.0 MPa. Prosopis glandulosa at Harper's Well is able to maintain open stomata during high temperatures, high vapor pressure deficit and at low estimated turgor pressure. Leaf resistance measurements indicate that stomata are open primarily in the morning, but may reopen in the afternoon in trees with greater water resources. Osmotic potentials of juvenile shoots were higher (-1.0 to-2.5 MPa) than mature shoots (-3.5 MPa). Estimated turgor potential remained low (0.1-0.2 MPa) during the morning and early afternoon. Estimated turgor pressure increased from August to September as temperatures and vapor pressure deficit decreased. Leaf conductance was strongly associated with leaf vapor pressure deficit and estimated turgor potential but poorly associated with xylem pressure potential. Prosopis stomata seem to be uncoupled from tissue water potential until-4.8 MPa is reached.