University of California, Riverside

Center for Conservation Biology

Award Recipients

2011 Shipley Skinner Awardees & Abstracts


ITNI Method: Evaluating nitrogen deposition to coastal sage scrub communities

Dr. Jim Sickman & Amanda Cobbs-Russell

The Integrated Total Nitrogen Input (ITNI) method is a technique for evaluating nitrogen deposition by utilizing plants as collection interfaces. The ITNI method employs a plant-liquid- soil system (PLS system) in which a plant is grown in nitrogen-free sand and labeled with 15N tracer while growing in a greenhouse. Upon deployment into the environment, the 15N tracer in the plant tissues is diluted as a result of atmospheric nitrogen deposition input via gaseous, leaf and root uptake. At the end of the sampling period, all components of the plant and system are harvested and analyzed on a mass spectrometer to determine the degree of dilution of the tracer. The 15N values obtained will be incorporated into a mass balance equation that accounts for the total deposition occurring on the PLS system surfaces and yields the total nitrogen uptake from the atmosphere. In this study, we will employ Coastal Sage Scrub species, a declining native California plant assemblage, to determine total nitrogen deposition occurring in the Inland Empire of Southern California. Traditional nitrogen deposition collection devices such as throughfall and ion exchange resins will be co-located with the ITNI PLS system to asses the accuracy of those traditional collectors. In addition, previously calculated ecosystem critical loads of nitrogen deposition will be evaluated relative to the ITNI deposition rates and CSS species specific nitrogen deposition rates will be determined.

Predator-free habitat in southern California’s threatened ephemeral ponds

Dr. Kurt Anderson & Ashkaan Fahimipour

Alterations to the spatial arrangement and water retention time of California’s native ephemeral ponds are a result of extensive habitat destruction over the last century. The spatial and temporal profiles of these ponds are important drivers of community structure, resulting in transient periods of predator-free habitat (PFH) following the regular drying and re-wetting events that reset succession. This transient period is attributed to the lag in the establishment of predator species who arrive later in assembly and colonize proportionately to their resource densities. There is evidence that PFH may benefit a number of broadly classified groups of organisms like “prey,” “mosquitos,” and “herbivores.” Conversely, evidence of keystone predation in ephemeral ponds suggestwhat may be best for “prey,” on the whole, may not bode well for the endemic and listed taxa that exploit these habitats and are rare in occurrence. It follows that changes to PFH has unknown consequences for the species of concern in California’s ephemeral ponds. The goal of this study is to determine (1) how species of concern react to PFH, and (2) whether this response changes with increasing pond isolation. To answer question (1), experimental mesocosms (plastic wading pools) will be placed at UC Irvine’s San Joaquin Freshwater Marsh Reserve and will receive one of two PFH treatments (“predators added” or “predators excluded”). If PFH facilitates prey occurrence, we expect to see higher species richness in those ponds undergoing the “predator excluded” treatment. Conversely, if keystone predation is a fundamental driver of pond structure, we expect to see the highest levels of richness in the “predators added” treatments. By measuring the relative abundance and biomass of each species, we can differentiate between what is best for “prey” and what is best for species of concern. We will answer question (2) by comparing richness patterns among PFH treatments across two isolation treatments (ponds placed 10m or 400m from a source pond). Because populations are less dense in isolated ponds, the importance of a keystone predator in subduing dominant competitors may be reduced in these habitats. Isolation can also have varying consequences for organisms with different dispersal modes (e.g. wind, flying, hitchhiking). The relative impact of PFH may change barring differing pre-colonization filters on these organism types. This work will inform critical regional and multiple-species management problems by providing a predictable framework for conserving species of concern in one of California’s most endangered habitats.

Predicting colonization patterns of habitat islands to post-fire lands in Joshua Tree National Park

Dr. Kurt Anderson & Heather Hulton

Habitat loss and fragmentation are the leading causes of biodiversity loss, and the ecological consequences of habitat loss and fragmentation differ depending on the spatial configuration of the landscape and how this influences colonization rates. Joshua Tree National Park (JTNP) in southern California is experiencing habitat loss and fragmentation due to an increase in fire size and frequency, which is facilitated by the invasion of non-native grasses. Even 65 years after a burn, a site within JTNP has not approached its pre-burned vegetation character. One conservation strategy that JTNP managers are implementing is planting vegetation patches within the burned areas, but the most cost-effective planting configuration is unknown. We will examine the influence of landscape structure on rodent and arthropod colonization patterns along with vegetation structure as a way to assess how alternative planting schemes might influence resulting community dynamics and restoration success. Our project will focus on empirically and theoretically predicting colonization patterns in a fragmented habitat. There are three main objectives to our study: (1) empirically determine vegetation and wildlife succession rates when influenced by patch dynamics, (2) empirically determine which species are most susceptible to disturbances when influenced by patch dynamics, and (3) create a predictive model of habitat patch colonization patterns over an extended period of time with an imposed disturbance regime to determine the most cost-effective spatial patch configuration.

The relationship of giant reed control to the long-term success of riparian restoration

Dr. Jodie S. Holt & Kai T. Palenscar

Considered one of the worst invasive species wherever it occurs, giant reed (Arundo donax) is a clonal grass which infests the waterways of California and provides poor wildlife habitat. Invasive species removal creates gaps in the community which will be filled by plants over time. These gaps may be filled by native species or reinvaded by locally common invasive species. My research investigates the role of giant reed control methods in the long-term success of riparian restoration. My hypothesis states that methods of giant reed management affect the subsequent trajectory of establishing vegetation and long-term habitat composition. Older giant reed removal sites (>5yrs) across southern California will be sampled for plant composition, density, and canopy cover, and soil moisture and temperature over the summer and fall 2011. I predict that methods incorporating chemical treatments applied to giant reed during the initial phase of control will promote subsequent establishment of more native cover than in sites where other control methods were used. Discussions with land managers suggest this relationship, but the variability between sites and the dynamic nature of the ecosystem make conclusions difficult. We also predict that control combined with native replanting, resulting in higher native canopy cover, will promote more native than exotic weed cover. Multiple regression analysis will be used to test for relationships among these variables.

Natural herbivory on Brassica tournefortii: A determination of background community structure

Dr. Rick Redak & Dr. Tim Paine

The Southwestern portion of the United States (Southern California, Arizona, portions of New Mexico and Texas) have been significantly invaded by the exotic mustard Brassica tournefortii. This is especially true for the more xeric areas of desert and coastal sage ecosystems. Although several methods of management and control of this invasive weed have been evaluated, none are suitable for large-scale implementation due to financial constraints and potential secondary negative impacts of the control technique itself. One approach that has not been investigated, nor attempted, is the use of native, or exotic, herbivorous arthropods to limit the spread of B. tournefortii. One major impediment to this latter approach is the entire lack of knowledge regarding what herbivores are currently actually feeding on the plant. Without that knowledge base, neither the manipulation of existing herbivore communities, nor the importation and release of exotic herbivores can be attempted. The sole objective of the research proposed here is to quantify and describe the arthropod herbivore community currently occurring on B. tournefortii within a variety of habitats located in Southern California. Without such information in hand, further consideration of the use of biological control by insects for B. tournefortii management will be limited if not impossible. Consequently, the review committee should consider this proposal a “first step” along the path to developing a biological control based management approach to limiting and controlling the spread of B. tournefortii. Currently, B. tournefortii is becoming a significant weedy pest for the Shipley-Skinner Reserve (and the majority of Southern California as well!) and the results of this research will have direct benefit to any biological control-based management strategy considered for future implementation on the reserve.

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