Andrea P. Loayza

The ecology, distribution and conservation status of Myrcianthes coquimbensis: a globally endangered endemic shrub of the Chilean Coastal Desert

Background: Myrcianthes coquimbensis is an endangered shrub endemic to Chile. No published account is known about its biology, ecology or threats to its continued existence. Aims: To document the current state of knowledge of M. coquimbensis regarding its geographic distribution, and population and reproductive parameters, and to evaluate threats in its distribution range. Methods: Historical records and recent survey data of 110 localities were used to characterise its known distribution. Plots were established in seven localities to determine the proportion of flowering individuals, recruitment and estimate population size and structure. Finally, levels of post-dispersal seed predation were determined in one locality. Results: The current distribution of M. coquimbensis extends along 82.8 km of the Chilean coast, where the species is mainly threatened by habitat loss. Only 13% of the individuals flowered during 2010, and 66% of these plants lost their entire flower crop due to desiccation. Few seeds (7.5%) were lost to post-dispersal seed predation. The populations are composed mainly of adult plants (70% of the individuals), and little to no recruitment was observed. Conclusions: M. coquimbensis populations are threatened by habitat loss and are not naturally recruiting through sexual reproduction. This exemplifies a case where studies on the ecology of a species are urgently needed to be able to design effective conservation and management plans.

Seed predation by rodents results in directed dispersal of viable seed fragments of an endangered desert shrub

Seed predation and seed dispersal are important ecological processes with antagonistic effects on plant recruitment. In the southern edge of the Atacama Desert in Chile, Myrcianthes coquimbensis is an endangered, large-seeded, vertebrate-dispersed shrub that in the present-day has no known dispersers. Native rodents hoard and eat the seeds of M. coquimbensis but leave viable seed fragments at the hoarding sites; soil interspaces within rock outcrops where seedlings recruit. Here we examined whether rodents act as effective dispersers of M. coquimbensis by discarding viable seed fragments in sites suitable for recruitment. We simulated different levels of endosperm loss to determine if seedlings could develop from seed fragments. We assessed how frequently rodents discarded fragments, and the probability that these fragments produced seedlings. Finally, we compared emergence and seedling survival at the hoarding sites and in two other habitats where seeds arrive to evaluate the suitability of the hoarding sites. Seeds of M. coquimbensis developed seedlings even after 87% of their storage tissue was removed. Rodents left seed fragments in more than 50% of the trials; almost 60% of the discarded fragments produced seedlings. Seedlings did not emerge from open ground habitats, and emergence was higher under M. coquimbensis shrubs than in rock habitats. Survival of two-year-old seedlings was higher in rock habitats than under conspecific adult shrubs. Our results suggest that rodents may play a dual role in the recruitment dynamics of M. coquimbensis, acting simultaneously as seed predators and effective dispersers. Therefore, though seed predators impose costs, their net effect on plant fitness in this system—where dispersers of large-seeded species have been lost—is likely positive.

Effects of host plant and maternal feeding experience on population vital rates of a specialized leaf beetle

In herbivorous insects, the interaction between adult preference and progeny performance on specific host plants is modified by maternal feeding experience and host plant quality. Ultimately, changes in the strength of this interaction can affect insect population dynamics. In this study, we hypothesized that adult host plant preference influences progeny performance through a maternal feeding experience × host plant interaction, that is, the effect of adult feeding experience on progeny performance will depend on the host plant. Second, that decoupling of the preference–performance relationship due to host switching results in different population vital rates changing population dynamics. An increase in development time and a decrease in body size of individuals in the alternate host should decrease population growth. We tested these hypotheses using two lines of the tortoise beetle Chelymorpha varians Blanchard fed with two hosts (Convolvulus arvensis and Calystegia sepium). Maternal feeding experience treatments were crossed with host plant species, and the offspring’s developing time and adult size were measured. The host plant influence on the beetle’s population vital rates was tested using stage-structured matrix population models and life table response experiments. Host plant preference affected offspring body size through a host plant effect that contributed to adaptive life history responses only in the better quality host. C. varians’ population growth was positive when fed with either host; comparatively, however, C. sepium had a negative effect on growth by reducing all transition probabilities of the life cycle stages of the beetle. Here, we show that individuals of C. varians prefer and perform differently on distinct hosts and that these patterns influence population vital rates in different ways. When beetles prefer the host plant where their progeny performs best, life history responses and life stage transitions lead to higher population growth; otherwise, growth rate decreases.

Contrasting responses to water-deficit among Encelia canescens populations distributed along an aridity gradient

PREMISE OF THE STUDY Drought is the most limiting factor for plant growth and recruitment in arid environments. For widespread species, however, plant responses to drought can vary across populations because environmental conditions can vary along the range of the species. Here, we assessed whether plants of Encelia canescens from different populations along an aridity gradient in the Atacama Desert respond differently to water-deficit conditions. METHODS We conducted a common-garden experiment using plants grown from seeds from three populations distributed along an aridity gradient to test for differences in relative growth rate (RGR), biomass, root to shoot ratios, and photosynthesis between watered and water-deficit plants. Additionally, we examined the relationship between root to shoot ratios with RGR and total plant biomass along the gradient. KEY RESULTS Water deficit affected root to shoot ratios, biomass, and RGR, but not photosynthesis. Populations varied in RGR and biomass; plants from the most arid population had higher RGRs, but lower biomass than those from the least arid population. In watered conditions, root to shoot ratios did not vary with RGR or biomass. Conversely, with the water deficit, root to shoot ratios were negatively and positively related to biomass and RGR, respectively. CONCLUSIONS Response to water deficit differed among E. canescens populations; plants from the lowest rainfall environment adjusted root to shoot ratios, which may have allowed for equal biomass production across treatments. In contrast, plants from the wettest population did not adjust root to shoot ratios, but were reduced in biomass. These morphological and physiological changes to water availability showed that populations can use different strategies to cope with water deficit.

Fruit Size Determines the Role of Three Scatter-Hoarding Rodents as Dispersers or Seed Predators of a Fleshy-Fruited Atacama Desert Shrub

Scatter-hoarding rodents can act as both predators and dispersers for many large-seeded plants because they cache seeds for future use, but occasionally forget them in sites with high survival and establishment probabilities. The most important fruit or seed trait influencing rodent foraging behavior is seed size; rodents prefer large seeds because they have higher nutritional content, but this preference can be counterbalanced by the higher costs of handling larger seeds. We designed a cafeteria experiment to assess whether fruit and seed size of Myrcianthes coquimbensis, an endangered desert shrub, influence the decision-making process during foraging by three species of scatter-hoarding rodents differing in body size: Abrothrix olivaceus, Phyllotis darwini and Octodon degus. We found that the size of fruits and seeds influenced foraging behavior in the three rodent species; the probability of a fruit being harvested and hoarded was higher for larger fruits than for smaller ones. Patterns of fruit size preference were not affected by rodent size; all species were able to hoard fruits within the entire range of sizes offered. Finally, fruit and seed size had no effect on the probability of seed predation, rodents typically ate only the fleshy pulp of the fruits offered and discarded whole, intact seeds. In conclusion, our results reveal that larger M. coquimbensis fruits have higher probabilities of being harvested, and ultimately of its seeds being hoarded and dispersed by scatter-hoarding rodents. As this plant has no other dispersers, rodents play an important role in its recruitment dynamics.

Conspecific plants are better ‘nurses’ than rocks: consistent results revealing intraspecific facilitation as a process that promotes establishment in a hyper-arid environment

In stressful environments, nurse elements, such as shrubs or rocks, facilitate plant recruitment by providing less severe environments for seed germination and seedling survival. As seedlings develop, however, they may compete for resources with their nurse when it is a plant instead of a rock. We examined the role of conspecific plants and rocks as nurses of an endangered Atacama-Desert shrub. Establishment was highest under conspecific plants, revealing that in stressful environments plants can facilitate establishment of their own species. Our study contrasts findings from other environments where recruitment is lowest near plants of the same species.

Germination, seedling performance, and root production after simulated partial seed predation of a threatened Atacama Desert shrub

BackgroundSeed loss to predators is a common phenomenon across plant communities and an important determinant of plant recruitment. Although seed predators commonly destroy the entire seed, partial seed consumption has been reported for many species; however, the degree to which seed mass loss affects germination dynamics and survival of new individuals has been poorly documented. We simulated seed damage in natural conditions to examine how different levels of cotyledonary reserve removal affect germination dynamics and seedling performance of Myrcianthes coquimbensis (Myrtaceae), a threatened Atacama Desert shrub. The experiment combined two levels of seed maturity with three levels of seed mass loss.ResultsRemoval of the cotyledon reserves and seed maturity negatively affected the odds and the temporality of seedling emergence; nonetheless, seedlings were able to emerge from seed fragments, of either mature or immature seeds, that lost up to 75% of their original mass. Removal of cotyledonary reserves had negative effects on seedling size but no effect on root:shoot ratios.ConclusionsOur findings indicate that the loss of cotyledonary reserves in M. coquimbensis seeds is not necessarily lethal. Moreover, we posit that tolerance to partial seed consumption is likely a key reproductive strategy, which enables recruitment in this species.