Insect visitation of peduncular and petiolar extrafloral nectar glands on castor bean (Ricinus communis L.) plants in Southern California

Castor bean (Ricinus communis L.) is a myrmecophytic plant species with specialized extrafloral nectar (EFN) glands that serve to attract predatory insects, which in return defend plant-tissues against herbivores. The EFN glands on castor bean plants are located along the leaf petioles as well as on the peduncles of its imperfect (unisexual) flowers. This field-project evaluates the richness, diversity, and species assemblage of insects visiting EFN glands located on (female and male) flower peduncles and leaf petioles on castor bean plants growing in a Southern California coastal landscape. We detected that EFN glands on female-flower peduncles were visited by an insect community that was distinct from that of the other two EFN gland types on castor bean. Additionally, the insects visiting EFN glands on male-flower peduncles more closely resembled those observed visiting EFN glands on leaf petioles. We conclude that the observed differences in the biotic defense of foliar and unisexual floral tissues on castor bean are congruent with the optimal plant-defense strategy of a monoecious pioneer species

Differential Resource allocation of black mustard plants (Brassica nigra L.) with proximity to black walnut trees (Jug/ans californica L.) in a Southern California Riparian ecosystem

The invasive forb Brassica nigra (black mustard) and the native tree Jug/ans californica (black walnut) are allelopathic species that suppress the growth of neighboring plants. This study evaluates how allocation to root, reproductive, and photosynthetic biomass in B. nigra was affected with proximity to J. califomica. We hypothesized that a joint suppressive effect would lead to lower root biomass allocation in B. nigra near J. californica due to reduced interspecific competition. Our results indicate that B. nigra plants growing near J. califomica had significantly lower root : total biomass ratios, and provide insights into how to effectively control this invasive species

Photosynthetic Characterization of Invasive Plant Diversity in Los Angeles County from 1830-2010

The increase in atmospheric CO2 levels due to climate change may greatly impact invasive plant species, which are non-native organisms that spread unchecked in space and negatively impact native organisms. The success of these invasives may be related to specific traits, such as their photosynthetic pathway. We acquired the specimen information for invasive species registered in the Consortium for California Herbaria of the University of California Berkeley to evaluate the community dynamics of 1,000 invasive species in Los Angeles County. We found that both diversity and richness of invasive plant species has increased over a period of 180 years. We hypothesize that the pattern of occurrence of a given photosynthetic pathway may correspond with historical increases in atmospheric CO2 concentrations, therein favoring invasives with a C3 photosynthetic strategy. We utilized the primary literature to identify the photosynthetic pathway for all of the invasive plant species in our database, then used curve-fitting techniques to evaluate the change in richness for C3, C4, and CAM. We found evidence to support that C3 invasives were indeed favored over C4 and CAM. We are currently examining stomatal densities of historical specimens in order to link this finding to CO2 levels. If stomatal densities of these C3 invasives has decreased, they have been responding to increased CO2, supporting our hypothesis

Differential bait preference and rate of attraction by Argentine ants (Linepithema humile Mayr) at freshwater and saltwater marsh sites in southern California

Ants are a type of foraging insect species which harvests food resources based on availability. When ants locate food resources that are scarce within their habitat, they tend to be more strongly attracted to that food resource. This study used protein, carbohydrate and control based baits to examine if there was a deficiency in resources demonstrated by the ants at two different wetland habitats. We sampled Argentine ants (Linepithema humileMayr) within the saltwater and freshwater marshes of Ballona Wetlands in Los Angeles, CA. We found significant differences in the rapid deployment of Argentine ants towards protein baits over carbohydrate and control baits. We saw more Argentine ants at the protein baits in the saltwater marshes than in the freshwater marshes. We propose that a protein limitation exists in both wetland habitats with increased protein limitation in the saltwater marshes

Preliminary Report: A survey of aggressive behaviors in the American coot (Fulica americana) at Ballona Wetlands, California

Understanding interspecific and intraspecific aggression is important for wildlife management and sustainability of populations. The objective of this study was to evaluate whether there is a difference in number of occurrences of interspecific aggression between American coots (Fulica americana) and mallard ducks (Anas platyrhynchos) and intraspecific aggression among American coots in the Ballona wetland habitat of Southern California. Trends in literature describe coots as highly aggressive toward other coots year-round and toward other bird species during the breeding season. Because we conducted observations outside the breeding season, we hypothesized that more instances of intraspecific aggression would be observed. We found a significant difference between the number of occurrences of interspecific and intraspecific aggression based on four behaviors specific for American coots: charging, paired display, splattering, and churning. There were more instances of intraspecific aggressive encounters than interspecific aggressive encounters, which indicate the interacting species at Ballona are not competing for resources and their respective niches may not overlap

Preliminary Report: Investigation of Castor Bean Investment in Extra-Floral Nectary Glands and Reproduction

The castor bean plant, Ricinus communis has EFN (extrafloral nectary) glands that attract ants which provide defense for the plant. From this, we proposed the idea that the more EFN glands a plant has, the more ants will visit the plant, and therefore provide more defense to the plant. Using the principle of allocation, we deduced that a plant using this strategy would invest less energy in reproduction than in defense, given that growth is fixed. In this experiment we examined the number of reproductive flowers that a plant produces (male and female) in relation to the number of EFN glands on the petiole. We predicted that the more EFN glands present, the fewer flowers will be found on the plant. When comparing males and females, we found that there was instead a positive correlation between female flowers and EFN glands but no correlation between male flowers and EFN glands. From our results and analysis, we concluded that even though more energy was invested in defense (total number of EFN glands) the castor bean plant still produced more female reproductive flowers. These results contradict our assumptions based on the principle of allocation and reveals possibilities of control issues and biotic versus abiotic (chemical) discretion in defense investments

Characterization of Sugar Diversity in Floral and Extra-Floral Nectar from the Coastal Coral Tree (Erythrina caffra Thunb.) in Southern California

The Coastal Coral Tree (Erythrina caffra Thunb.) produces floral nectar (FN) that serves to attract pollinating insects, but also secretes nectar from extra-floral (EFN) glands that serves to at-tract predatory insects, such as ants. While stu-dies on myrmecophytes (i.e. specialized plants that attract and interact with ants) have primarily focused on interspecific evaluations of EFN chemistry, the Coastal Coral tree offers an op-portunity to contrast intraspecific nectar chemi-stry with differing evolutionary and ecological functions. We hypothesized that the richness of (molecular) sugar species, relative concentra-tions, and diversity of sugars in FN and foliar EFN would diverge due to differences in the ecological role of the two types of nectar. High performance liquid chromatography with refrac-tive index detection was used to identify the richness of sugar species (based on retention time), measure the relative concentrations, and evaluate the diversity of sugars in FN and foliar EFN secretions. We detected sugar species unique to each gland type and reported signifi-cant differences in the relative concentration of one sugar species common to both gland types. While the mean diversity index of sugars was similar for both gland types, the diversity of fo-liar EFN sugars was significantly more variable than that of FN sugars. The composition of FN showed little variation, and was reflective of its fundamental role in plant reproduction. Foliar EFN, however, demonstrated the variability ex-pected of a context-dependent myrmecophyte that interacts with a facultative ant species as-semblage across a mosaic of abiotic and biotic conditions

A preliminary study of Ricinus communis survivorship at Ballona Wetlands and Temescal Canyon, Los Angeles, California

Invasive plants such as Castor bean (Ricinus communis) are known to threaten ecosystems due to their competition for resources. The Ballona Wetlands and Temescal Canyon managers employ different techniques to manage the spread of R. communis, potentially resulting in differences in plant survivorship. To investigate this possibility, height of the stems of individual R. communis plants at each site were recorded in order to assign them to cohort groups. Based on the hypothesis predicted that R. communis would have a similar cohort structure at both sites but would exhibit higher survivorship at Temescal Canyon, where R. communis are removed less frequently than at the Ballona Wetlands. However, results indicate that management does not affect cohort structure or stability at either site, but rather, it may have contributed to the significantly higher overall survivorship of R. communis at Temescal Canyon

Sub-Canopy Temperature Dynamics of a Native Tree Plantation from a Lowland Tropical Rainforest in Costa Rica

With urbanization encroaching upon forestlands, characterizing microclimates in secondary forests will be important for the sustainable management of microclimates in agroforestry systems. We used micro-sensors to characterize changes in temperature at different heights in the sub-canopy of both secondary forest and 15-year-old agroforestry plots. Results show that while agroforestry plots had different temperature profiles from the secondary forest, the monoculture plot (consisting of Pentaclethra macroloba) had temperatures similar to the profile found in the secondary forest. This suggests that the replication of temperature profiles in a secondary forest may be independent of the number of tree species in a plot (e.g. polyculture), but may instead depend on the density of a given trees species. These findings further suggest that characterizing temperature microclimates in secondary forests can serve to improve the ecological sustainability of agroforestry systems

Exploration of climate influences on the abundance of galls on red willow (Salix /aevigata) across two riparian communities in Southern California

In Southern California, the red willow (Sa/ix laevigata Bebb) hosts a variety of gall-inducing parasitic insects. However, little is known about the ecology of these parasites, particularly the characterization of their microclimate preferences. This study explores the relationship between microclimate and gall frequencies in S. laevigata in the Ballona Wetlands and Temescal Canyon, and gall count correlated with biotic and abiotic factors such as soil pH, soil moisture and willow density. Significantly more galls per leaf were found at Temescal Canyon than Ballona Wetlands. Although the number of galls per leaf correlated negatively with soil pH, soil moisture content and canopy openness, only site and gall location were found to significantly predict the number of galls. These results suggest that additional or interacting microclimate factors may influence gall frequencies between Temescal Canyon and the Ballona Wetlands