Demographic modeling of conservation strategies for the Yosemite toad (Anaxyrus canorus)

The Yosemite toad (Anaxyrus canorus) is an anuran species endemic to the Sierra Nevada in California that, like many amphibians globally, has suffered population declines. The documented decline in A. canorus populations across their historic range highlights the need for an effective management strategy to protect the species from future extirpation. For this study, I estimated survival rates of A. canorus using a Cormack-Jolly-Seber model populated with data from a demographic study. I then used a female-only post-birth pulse stochastic Lefkovitch matrix model using vital rates I estimated and from the literature to simulate the effect of different management scenarios and to optimize a supplementation or reintroduction management plan. Without any management action, small populations of A. canorus populations have ≥50% risk of quasi-extinction over the next 13 years. The implementation of effective management strategies is critical to prevent further extinction of existing small populations. My results suggest that the effectiveness of a supplementation or a reintroduction management plan is dependent on the initial population size of the receiving population, life stage at release and number of individuals released into a wild population. I found that supplementing small toad populations with female adults is the most effective supplementation strategy to increase the stochastic growth rate and minimize the risk of quasi-extinction. This thesis suggests that modeling A. canorus population dynamics and trends of extant populations can help inform conservation strategies

Complex Consequences of Herbivory and Interplant Cues in Three Annual Plants

Information exchange (or signaling) between plants following herbivore damage has recently been shown to affect plant responses to herbivory in relatively simple natural systems. In a large, manipulative field study using three annual plant species (Achyrachaena mollis, Lupinus nanus, and Sinapis arvensis), we tested whether experimental damage to a neighboring conspecific affected a plant's lifetime fitness and interactions with herbivores. By manipulating relatedness between plants, we assessed whether genetic relatedness of neighboring individuals influenced the outcome of having a damaged neighbor. Additionally, in laboratory feeding assays, we assessed whether damage to a neighboring plant specifically affected palatability to a generalist herbivore and, for S. arvensis, a specialist herbivore. Our study suggested a high level of contingency in the outcomes of plant signaling. For example, in the field, damaging a neighbor resulted in greater herbivory to A. mollis, but only when the damaged neighbor was a close relative. Similarly, in laboratory trials, the palatability of S. arvensis to a generalist herbivore increased after the plant was exposed to a damaged neighbor, while palatability to a specialist herbivore decreased. Across all species, damage to a neighbor resulted in decreased lifetime fitness, but only if neighbors were closely related. These results suggest that the outcomes of plant signaling within multi-species neighborhoods may be far more context-specific than has been previously shown. In particular, our study shows that herbivore interactions and signaling between plants are contingent on the genetic relationship between neighboring plants. Many factors affect the outcomes of plant signaling, and studies that clarify these factors will be necessary in order to assess the role of plant information exchange about herbivory in natural systems

Complex consequences of herbivory and interplant cues in three annual plants.

Information exchange (or signaling) between plants following herbivore damage has recently been shown to affect plant responses to herbivory in relatively simple natural systems. In a large, manipulative field study using three annual plant species (Achyrachaena mollis, Lupinus nanus, and Sinapis arvensis), we tested whether experimental damage to a neighboring conspecific affected a plant's lifetime fitness and interactions with herbivores. By manipulating relatedness between plants, we assessed whether genetic relatedness of neighboring individuals influenced the outcome of having a damaged neighbor. Additionally, in laboratory feeding assays, we assessed whether damage to a neighboring plant specifically affected palatability to a generalist herbivore and, for S. arvensis, a specialist herbivore. Our study suggested a high level of contingency in the outcomes of plant signaling. For example, in the field, damaging a neighbor resulted in greater herbivory to A. mollis, but only when the damaged neighbor was a close relative. Similarly, in laboratory trials, the palatability of S. arvensis to a generalist herbivore increased after the plant was exposed to a damaged neighbor, while palatability to a specialist herbivore decreased. Across all species, damage to a neighbor resulted in decreased lifetime fitness, but only if neighbors were closely related. These results suggest that the outcomes of plant signaling within multi-species neighborhoods may be far more context-specific than has been previously shown. In particular, our study shows that herbivore interactions and signaling between plants are contingent on the genetic relationship between neighboring plants. Many factors affect the outcomes of plant signaling, and studies that clarify these factors will be necessary in order to assess the role of plant information exchange about herbivory in natural systems

Data from: Complex consequences of herbivory and interplant cues in three annual plants

Information exchange (or signaling) between plants following herbivore damage has recently been shown to affect plant responses to herbivory in relatively simple natural systems. In a large, manipulative field study using three annual plant species (Achyrachaena mollis, Lupinus nanus, and Sinapis arvensis), we tested whether experimental damage to a neighboring conspecific affected a plant's lifetime fitness and interactions with herbivores. By manipulating relatedness between plants, we assessed whether genetic relatedness of neighboring individuals influenced the outcome of having a damaged neighbor. Additionally, in laboratory feeding assays, we assessed whether damage to a neighboring plant specifically affected palatability to a generalist herbivore and, for S. arvensis, a specialist herbivore. Our study suggested a high level of contingency in the outcomes of plant signaling. For example, in the field, damaging a neighbor resulted in greater herbivory to A. mollis, but only when the damaged neighbor was a close relative. Similarly, in laboratory trials, the palatability of S. arvensis to a generalist herbivore increased after the plant was exposed to a damaged neighbor, while palatability to a specialist herbivore decreased. Across all species, damage to a neighbor resulted in decreased lifetime fitness, but only if neighbors were closely related. These results suggest that the outcomes of plant signaling within multi-species neighborhoods may be far more context-specific than has been previously shown. In particular, our study shows that herbivore interactions and signaling between plants are contingent on the genetic relationship between neighboring plants. Many factors affect the outcomes of plant signaling, and studies that clarify these factors will be necessary in order to assess the role of plant information exchange about herbivory in natural systems

For the crucifer <i>Sinapis arvensis</i>, the effect of neighbor-wounding and relatedness (maternal siblings or unrelated) on various measures of leaf palatability to a specialist herbivore (<i>Pieris</i>).

<p>The potted plant was exposed to a damaged or undamaged neighbor in the field for 2 days. At this point the plant was moved indoors, and a no-choice feeding trial with a neonate <i>Pieris</i> caterpillar was initiated. Graphs show a) the percent leaf area removed by <i>Pieris</i> (log-transformed), and b) <i>Pieris</i> caterpillar mass (log-transformed) at the end of the feeding trial. Bars indicate least square mean +/− SE.</p

The effect of neighbor wounding and relatedness (maternal siblings or unrelated) on subsequent herbivore damage (log-transformed percent leaf damage) to conspecific neighbors of three experimental plant species in the field.

<p>Least Square Mean +/− SE.</p

The effect of neighbor wounding and relatedness (maternal siblings or unrelated) on developmental phenology of conspecific neighbors of three experimental plant species in the field.

<p>Filled bars are the number of bolting plants, and empty bars are the number of flowering plants in each treatment two weeks after the wounding of neighboring plants (May 9, 2011). The total number of plants in each treatment is shown on each bar.</p

The effect of neighbor wounding and relatedness (maternal siblings or unrelated) on lifetime seed production (log-transformed) of three experimental plant species in the field.

<p>Least Square Mean +/− SE.</p

Mixed model results for effects of a neighbor damage treatment, plant species and neighbor relatedness treatments on leaf damage to “receivers” in the field.

<p>Models account for sampling date and covariate factors relating to plant size and pre-treatment damage levels. Emphasis indicates significance at the P = 0.05 level.</p

A summary of experimental results.

<p>For each response variable, the bar represents the log response ratio where the conspecific neighbor (emitter) was experimentally wounded (W) versus unwounded (UW). A positive bar indicates that the response variable of the receiver plant was greater when the emitting plant was wounded than when it was unwounded; a negative bar indicates the converse. The effect of neighbor wounding is shown both related and unrelated pairs of each of the three plant species in this study. For example, in related pairs of <i>A. mollis</i>, wounding to a neighbor increased the leaf removal that a focal plant suffered compared to focal plants with unwounded neighbors. Palatability to a specialist herbivore (<i>Pieris</i>) could only be assessed for one plant species (<i>S. arvensis</i>) and was not tested (NT) for other plant species.</p