I synthesized monitoring results for vertebrates at Organ Pipe Cactus National Monument (ORPI), 1987-1998. Small mammals, lizards, and predators were studied using ongoing Ecological Monitoring Program (EMP) protocols (trap grids; transects) and other methods (drift-fences, visual encounter, road-cruising). EMP protocols for rodents and lizards performed well, but some recalibration is needed. Populations declined to observed minima during a 1989-1990 drought, and increased with strong rains during 1990-1995. Small rodents (pocket mice) increased fastest, but declined first, after 1992. The medium-sized Merriam's kangaroo rat: increased to a 1994 peak and then also collapsed. The larger packrat increased most slowly, not declining until after 1995. These temporal differences are consistent with a tradeoff of capacity for increase with resistance to predation pressure. After post-drought increases, most lizard populations declined when predator pressure became high, after 1992, and then increased during dry years after 1995, while predators declined. Endothermic predators were monitored by simple daily record-keeping. They increased 3-4 fold from 1989-1995, with subsequent declines. A literature review showed two subguilds: a small-prey group, which increased rapidly in 1991-1993, and a larger-prey group, which increased more slowly. For most snakes, population fluctuations during 1989-1998 did not appear dramatic. Western diamondback rattlesnakes and coachwhips were the most important mammal- and reptile-eating snakes, respectively. Large cohorts of young rattlesnakes were produced during 1992 and 1993. The western diamondback approximately doubled by 1995, and the coachwhip increased during 1991-1993. I summarized results for prey taxa, using bivariate correlation and path analysis. I used precipitation as a proxy for food productivity, and constructed predation pressure indices that combined snakes and endotherms. Conspecific density was the most consistent (negative) correlate of population growth. Predation (negative) and productivity (positive) also had relatively consistent associations with annual prey population growth. Lizard population growth was positively correlated with summer rain, whereas some rodents and endothermic predators had positive correlations with winter rain. The analysis supported a competitive effect of Merriam's kangaroo rat on pocket mice. I recommend adding predator monitoring to the EMP, and propose that resource management and academic ecology may develop a beneficial collaboration in the context of monitoring programs.

This work focused on how visual and olfactory cue use by insects affect tritrophic interactions among the Arizona walnut, Juglans major (Juglandaceae), the fly Rhagoletis juglandis (Diptera: Tephritidae), whose larvae feed on the husk surrounding walnut fruits, and the parasitic wasp Biosteres juglandis (Hymenoptera: Braconidae: Opiinae) which oviposits in the fly larvae. The foraging behavior of female Biosteres juglandis was studied in the field and greenhouse, with specific attention paid to their use of visual and olfactory cues produced by walnut fruits harboring R. juglandis larvae. Field work demonstrated that wasps are successful in locating fruits infested with host larvae interspersed among uninfested fruits, and that they use fruit phenological traits (i.e. stage of rot) to do so. The method by which females appear to choose fruits in the field is functional, provided there are high host infestation levels. In greenhouse assays, fruit damage (apart from larval presence) was specifically identified as an important cue affecting wasp fruit choice. Wasps are also able to orient to infested fruits using only one type of cue, either olfactory or visual. Preliminary data from a pilot analysis of volatile compounds associated with infested, uninfested, and artificially damaged walnuts indicated that visual cues were more important than olfactory cues to free-foraging wasps. Rhagoletis juglandis adult females visit walnut fruits for oviposition, while adult males visit them to obtain matings. The effect of fruit color pattern on the behavior of male and female flies both inexperienced and experienced with real ripe walnuts was studied in the greenhouse. Overall, both sexes of flies exhibited a landing preference for plastic fruit models that appear ripe and uninfested, over models that appear infested. The behavior of both sexes may be driven by females who are attempting to provide offspring with the most possible food resources. Finally, the growth and germination of Arizona walnut seeds was followed to determine whether either was affected by infestation of the husk by R. juglandis. Although infested fruits were more likely to fall off a tree sooner, this did not affect the size of a walnut or its ability to germinate.

Fungal endophytes associated with leaves of woody plants are thought to be diverse and abundant, especially in tropical forests. However, associations of endophytes with tropical woody angiosperms have not been characterized in detail. In this dissertation, I assess: (1) the scale of endophyte biodiversity in a tropical forest; (2) ecological, temporal, and host-mediated factors influencing endophyte abundance in leaves of tropical trees; (3) utility of endophyte morphospecies as functional taxonomic units; and (4) the nature of endophyte-host interactions. To characterize endophyte biodiversity, I measured endophyte richness in asymptomatic leaves of two distantly related, but co-occurring, host species in lowland forest in central Panama. I found that endophytes are highly diverse within leaves, plants, and host species, and that they demonstrate both host preference and spatial heterogeneity. To determine factors influencing abundance of tropical endophytes, I assessed effects of inoculum abundance, duration of exposure to inoculum, phylogenetic position of host, and leaf traits (e.g., chemical and structural defenses) on rates of endophyte infection. I found that endophyte abundance is sensitive to inoculum abundance in the short term, but to duration of exposure over the long term. In turn, inoculum abundance is sensitive to canopy cover, time of day, and time since precipitation. Generally, neither leaf traits nor phylogenetic position of hosts is related to rates of endophyte infection: endophytes occur with consistently high abundance and diversity among representatives of 14 orders of angiosperms. To assess utility of morphospecies as taxonomic units, I compared diversity and taxonomic composition among morphospecies of endophytes as delineated using several criteria, and among species as inferred using nrDNA data. I found that conservatively designated morphospecies can approximate species boundaries as defined by nrDNA data for diverse Ascomycota. Finally, I examined effects of endophytes on (1) minimum leaf conductance, a measure of water loss from leaves under drought conditions; and (2) leaf mortality and necrosis in the presence of a foliar pathogen for a focal host. I found that endophytes may cost their hosts by increasing water loss under conditions of severe drought, but that they also may play an important role in host defense against pathogens.

Forest fire is a keystone ecological process in coniferous forests of southwestern North America. This dissertation examines a fire regime in the Jemez Mountains of northern New Mexico, USA, based on an original data set collected from Monument Canyon Research Natural Area (MCN). First, I examine scale dependence in the fire regime. Statistical descriptors of the fire regime, such as fire frequency and mean fire interval, are scale-dependent. I describe the theory of the event-area (EA) relationship, analogous to the species-area relationship, for events distributed in space and time; the interval-area (IA) relationship, is a related form for fire intervals. The EA and IA also allow estimation of the annual fire frame (AFF), the area within which fire occurs annually on average. The slope of the EA is a metric of spatio-temporal synchrony of events across multiple spatial scales. The second chapter concerns the temporal distribution of fire events. I outline a theory of fire interval probability from first principles in fire ecology and statistics. Fires are conditional events resulting from interaction of multiple contingent factors that must be satisfied for an event to occur. Outcomes of this kind represent a multiplicative process for which a lognormal model is the limiting distribution. I examine the application of this framework to two probability models, the Weibull and lognormal distributions, which can be used to characterize the distribution of fire intervals over time. The final chapter addresses the theory and effects of sample size in fire history. Analytical methods (including composite fire records) are used in fire history to minimize error in inference. I describe a theory of the collector's curve based on accumulation of sets of discrete events and the probability of recording a fire as a function of sample size. I propose a nonlinear regression method for the Monument Canyon data set to correct for differences in sample size among composite fire records. All measures of the fire regime reflected sensitivity to sample size, but these differences can be corrected in part by applying the regression correction, which can increase confidence in quantitative estimates of the fire regime.

I examined resistance to cold temperature in seven Drosophila species from different habitats to determine the lower limits of cold tolerance. Three separate tests were administered to measure the: (1) response to a cold-shock exposure; (2) extent to which a short-term survival strategy, rapid cold hardening, was utilized by each species; and (3) degree to which each species would respond to a prolonged exposure at 0°C. As expected, the temperate-montane species, D. pseudoobscura, was the most cold-tolerant, whereas the least cold-tolerant was the tropical species, D. paulistorum. The two cosmopolitan species, D. hydei and D. melanogaster, and the three Sonoran Desert endemic species, D. mojavensis, D. nigrospiracula, and D. mettleri, demonstrated intermediate levels of cold-tolerance. Of the five species tested for rapid cold hardening, all exhibited the response, including the tropical representative. The results for the 0°C test paralleled the results of the cold shock test. The desert species tested proved surprisingly cold-tolerant, especially D. mojavensis.

Two factors affecting the mutualism between Myrmecocystus mendax and Publilia modesta are investigated. These factors are the seasonal time frame during which the mutualism is maintained and the behavior of individual workers tending membracid aggregations. Results of this study show that Publilia modesta makes seasonal migrations via flight, makes use of a conifer as a long term host, mates on a substate distant from a suitable oviposition host, and changes color with the onset of ovarian development many months after metamorphosis. Membracid-tending Myrmecocystus mendax comprise a behaviorally distinct subcaste and behave in a manner consistent with optimal foraging theory by maintaining both site and resource fidelity.

Blood fed Culex quinquefasciatus were collected from residential and wetland sites in Tucson, Arizona for three years using CDC gravid traps. An ELISA distinguishing human, bird, dog, cat, and rabbit blood meals was used. In residential areas, approximately 47% of all identified blood meals were from humans, with fewer blood meals from bird, dog, cat, and rabbit. At Sweetwater Wetland, humans were also the most common host, with 11 (41%) identified blood meals. Birds were the hosts of 19% blood meals. Ten (seven residential, three wetland) mosquitoes were identified to have blood from both bird and human hosts. Since the transmission of West Nile Virus to humans is dependent on mosquitoes feeding both on birds and humans, this finding is particularly relevant. These data only describe the feeding choices of the mosquitoes collected from a limited number of sites in Tucson, and therefore, may not reflect feeding preferences more generally.

<p> Terrestrial litterfall is a well-documented subsidy of nutrients and organic matter to adjacent aquatic ecosystems. Nitrogen-fixing plants increase nutrient dynamics via nitrogen (N) - rich litterfall in both terrestrial and aquatic ecosystems, and the effects are often more pronounced when areas lacking native N₂-fixers are invaded. This study examined differences in organic matter and nutrient inputs from the invasive, N₂-fixing tree, <i>Prosopis pallida</i>, and the native, non N₂-fixing tree, <i>Thespesia populnea</i>, to determine effects on anchialine ponds on Hawai`i Island's leeward coast. My objectives were to quantify: 1) tree basal area and density surrounding the ponds, 2) quality and quantity of <i>P. pallida</i> and <i>T. populnea</i> litter inputs, 3) inorganic N content of soil surrounding the ponds, 4) leached nutrients from <i>P. pallida</i> and <i>T. populnea</i> leaf litter. These response variables were then compared to water nutrient concentrations (i.e., phosphate, nitrate, ammonium, dissolved organic carbon (C), and total dissolved N and phosphorus (P)) in the ponds of interest. Basal area, density, litterfall mass, total N and C inputs, and leachate values were similar between pond types categorized as <i>P. pallida</i> &ndash; or <i> T. populnea</i> &ndash; dominated. Foliar N concentrations were 28 percent higher in <i>P. pallida</i> &ndash; dominated ponds compared to <i>T. populnea</i> &ndash; dominated ponds, but foliar P concentrations were three times greater in <i>T. populnea</i> ponds than <i>P. pallida</i> ponds. Total P inputs were greater beneath <i>T. populnea</i> ponds and there was a positive correlation between <i>T. populnea</i> size and abundance and pond water phosphate concentrations. These results suggest that the N if influencing water quality in Hawaiian anchialine ponds more than the invasive N₂-fixing species, although high background water nutrient levels may be inhibiting our ability to detect any significant impacts. The transfer of <i>T. populnea</i>'s P-rich litter to pond water appears to have a strong influence on ecosystem functioning.</p>

<p> As herbivorous insects choose where to lay their eggs, maximizing larval performance (optimal oviposition) may be at odds with adult foraging (optimal foraging). Aspen leaf miners (<i>Phyllocnistis populiella</i>; ALM) may choose between leaves with or without extrafloral nectaries (EFNs) as oviposition sites on quaking aspen (<i>Populus tremuloides</i> Michx.). Reduced ALM mining on leaves with EFNs may be linked to predators that defend leaves and feed at EFNs, and to increased concentrations of secondary leaf compounds. However, direct responses of adult ALM to EFN expression may also explain differences in ALM mining among leaves with and without EFNs. ALM might be less likely to oviposit on leaves with EFNs because these leaves provide poor conditions for larval development. With choice experiments and surveys of ALM oviposition, we examined oviposition site preference in relation to EFN expression. In choice experiments and field surveys adults preferred to oviposit on leaves without EFNs. Increased oviposition was also observed on shoots with high EFN frequencies, suggesting a combination of optimal foraging and optimal oviposition, and a role of EFNs at scales above the leaf level. Higher predation on leaves with EFNs likely exerts selective pressure for the observed ALM oviposition preference for non-EFN leaves.</p>

<p>Anthropogenic contributions to global reactive N pools have more than doubled since the agricultural and industrial revolutions. Although N is an essential plant nutrient, enrichment of reactive N in air pollution can initiate a cascade of deleterious effects including increased smog and haze, ecosystem acidification, increased invasion of non-native grasses, and reduced biodiversity. However, the ecological impacts of N deposition in historically N-limited, semi-arid regions are not well understood. Here, I report the findings from field studies of automobile pollution in Grand Canyon National Park (GCNP; Study 1) and long-range N deposition from the nearest coal-fired power plant, the Navajo Generating Station (NGS; Study 2). To identify potential indicators of N enrichment, I measured four different metrics of N pollution: 1) atmospheric nitrogen oxides (NO_x) with Ogawa passive air samplers, 2) natural abundance &delta;¹⁵N signatures of soil and foliage of pinyon pine (<i>Pinus edulis</i>), 3) spectral analysis of pinyon pine foliar nitrogen, and 4) leaf area on pinyon pine branches. </p><p> In both studies, the amount of NO_x measured by the Ogawa samplers decreased significantly with increasing distance from N-source. In heavily trafficked sites in GCNP, atmospheric NO_x was 52% higher at the roadside compared to 30 m away from the road. Atmospheric NO_x on the Paria Plateau was 54% higher 25 km from NGS compared to 50 km away from the coal-fired power plant. Across both study areas, &delta;¹⁵N values in plant tissues reflected inputs from emission sources. According to our data, the biggest ground level N inputs in GCNP are from vehicular emissions, not NGS. Although I detected patterns in terrestrial responses to both small and larger-scale N deposition gradients, future field studies focused on plant community composition and sensitive biological indicators are needed to determine ramifications of elevated N inputs caused by pollution from motor vehicles and power plants. </p>