Luis Marone

Timing and spatial patterning of seed dispersal and redistribution in a South American warm desert

We measured newly-produced seeds entering the soil (Potential Seed Bank) to assess the timing and spatial patterning of Phase I dispersal in the central Monte desert, Argentina. Rates of forb- (6.13 mg m-2 d-1) and shrub-seed input (48.9 mg m-2 d-1) were maximum in early summer. The rate of grass-seed input, instead, was similar in early and late summer (7 to 8 mg m-2 d-1). About 90% of forb- and shrub-seed mass entered the habitat through protected (i.e., under canopy) areas, whereas 70% of grass-seed mass did so through exposed areas. Adult plant location and the uneven impact of wind on shrub, forb and grass seeds may explain such patterns.We also compared the Potential Seed Bank with the soil seed bank in the following spring (Realized Seed Bank). Seeds that form transient banks in other ecosystems (e.g., shrub seeds of the genus Larrea, or perennial grass seeds like those of Pappophorum and Trichloris) prevailed in the Potential Seed Bank. Some annual forb seeds, instead, appeared to form a more persistent seed bank, and prevailed in the Realized Seed Bank (e.g., Chenopodium). Horizontal redistribution did not affect the spatial patterning of forb and shrub seeds, but produced a more homogeneous distribution of grass seeds in the habitat. The impact of wind could explain the redistribution pattern of grass seeds. Finally, we found almost 80% of total seeds in the top 2 cm of soil. The smallest grass and forb seeds (Sporobolus and Descurainia) as well as some medium-sized and large forb seeds (e.g., Glandularia, Sphaeralcea, Phacelia) were able to reach deeper soil layers in the central Monte desert.

ARE RESULTS OF ARTIFICIAL NEST EXPERIMENTS A VALID INDICATOR OF SUCCESS OF NATURAL NESTS

Abstract Studies using artificial nests to assess rates or patterns of nest predation have increased during recent decades. However, the critical assumption that temporal or spatial patterns of relative predation rates of artificial nests parallel those of natural nests has begun to be questioned. We compared the daily survival rate for 365 artificial nests with that estimated for 295 open nests of passerines, and analyzed the trends in survival rates for both nest types among three breeding seasons and three species of nest plants in the central Monte Desert, Argentina. Daily survival rate for artificial nests (0.737) was significantly lower than that for natural nests (0.925). Trends in survival rates of artificial nests over years and among species of nest plants only partially reflected those of natural nests. Our results support the well established finding that artificial nests may not accurately estimate actual rates of nest predation. Artificial nests may provide an additional source of data to natural nests when testing ecological hypotheses, but artificial nest experiments should be carefully designed (i.e., realistic) and should attempt to identify predators of artificial and natural nests to validate the experimental results.

SEED PREFERENCES IN SPARROW SPECIES OF THE MONTE DESERT, ARGENTINA: IMPLICATIONS FOR SEED-GRANIVORE INTERACTIONS

Abstract We assessed seed preference in four species of sparrows that are common to the central Monte desert of Argentina. Our hypotheses are that (1) sparrows always prefer grass over forb seeds and (2) different species of sparrows show the same preferences when consuming seeds. We presented seeds from eight species of plants (four grasses and four forbs) in both choice and nonchoice experiments. In general, sparrow species preferred grass over forb seeds, though one of them (Rufous-collared Sparrow [Zonotrichia capensis]) included one forb species (Parthenium hysterophorus) among its preferred seed items. Among grass seeds, sparrows avoided or showed less preference for the tiny seeds of Sporobolus cryptandrus, which suggests that seed weight may affect seed choice among grasses. Avoidance of most forb species, by contrast, could not be associated with seed size, probably because of the presence of unpalatable or toxic compounds in forb seeds. Experimental evidence suggests that the main feeding pressure of sparrows is clearly directed to grass seeds, which coincides with reported information on bird diet. Results support assertions that sparrows can cause a negative effect on the composition and abundance of grass seeds in the soil seed-bank, a necessary condition for birds in playing a significant role on grass population dynamics in the central Monte desert of Argentina. Preferencias por Semillas de los Emberízidos del Desierto del Monte, Argentina: Implicancias para la Interacción Semillas-granívoros

Microhabitat structure and avian nest predation risk in an open Argentinean woodland: an experimental study

Abstract We studied the effect of the general structure of the nest plant, especially the presence of thorns, and the structural homogeneity of the nest patch, on the vulnerability of nests to predation, using natural and artificial nests. Artificial nests placed in non-thorny plants had a significantly lower predation rate and higher daily survival rate than those in thorny plants. The addition of a ‘thorny microhabitat’ around the immediate proximity of nests placed in non-thorny plants did not have any effect on vulnerability of nests to predation. Conversely, natural nests were located in patches of habitat with a higher density of the species of plant that supported the nest compared to patches selected at random. However, daily survival rate was similar for natural nests placed in patches with a higher or lower density of the species of nest plant in the four bird species analysed. Similarly, survival of artificial nests did not increase with the presence of a higher number of plants similar to the nest plant in the nest patch. Thus, the observed patterns of survival for natural and artificial nests did not seem to support the potential prey-site hypotheses. Birds appeared to be the main nest predators in this ecosystem. Behavioural aspects of the identified predators and habitat structure could explain the lack of effect of thorns and nest patch characteristics on nest survival.

Tolerance to Dietary Phenolics and Diet Breadth in Three Seed‐eating Birds: Implications for Graminivory

The ability to cope with plant secondary compounds (PSCs) has profound implications for an animals behavior. In the present study, we assessed the tolerance to dietary phenolics in three seed-eating birds: Zonotrichia capensis, Saltatricula multicolor, and Diuca diuca, which differ in their diet breadth. Seeds in their habitat have distinct chemical composition: grass seeds have less PSCs, specifically, less total phenolics than forb seeds. Based on the detoxification limitation hypothesis and using published data of the natural history of these birds in the central Monte desert, we postulate that predominantly and exclusively graminivorous birds such as D. diuca and S. multicolor, respectively, are less tolerant due, in part, to a lower detoxification capacity than those with greater diet breadth, Z. capensis. To achieve this goal, we measured the food intake of diets varying in their concentration of tannic acid (TA). Indicators of tolerance were body mass change, food, TA and water intake, and glucuronic acid output throughout the experiment. Zonotrichia capensis performed better along the tolerance experiment: it maintained body mass from 0 to 4% TA diet, food and TA intake were higher than the other two species at the end of the experiment, and glucuronic acid output by Z. capensis was greater than D. diuca and S. multicolor from 2% TA diet until the end of the experiment. Our results suggest that Z. capensis is the most tolerant species and this physiological trait may explain their greater diet breadth.

NEOTROPICAL AUSTRAL MIGRANT LANDBIRDS: POPULATION TRENDS AND HABITAT USE IN THE CENTRAL MONTE DESERT, ARGENTINA

Abstract We studied density changes of two groups of Neotropical austral migrant landbirds—the South American temperate-tropical (SATT) and cold-temperate (SACT) migratory systems—in the main habitat types of the central Monte desert of Argentina (open Prosopis flexuosa woodland and Larrea cuneifolia shrubland) over 10 years. Five species, all tyrant flycatchers (Tyrannidae) made up SATT, whereas only two of the seven species of SACT were tyrannids. Densities of both SATT and SACT were higher in open woodland than in shrubland. SATT density did not differ among years, but SACT density did, having lower values in 1994 in both habitats. In subsequent years, SACT densities increased but did not reach values similar to those previous to 1994. The decline in 1994 coincided with a two-year drought period that began in 1993, but lower density in the following years did not appear to be related to climatic conditions in the study area, suggesting a low capacity of SACT species to recover population abundance after periods of stress. In contrast, SATT density was not associated with local climatic conditions, possibly because several SATT species used the study area only as a stopover site. During the breeding season, birds of both migratory systems disproportionately use the open woodland, which offers more sites to nest and feed than does the shrubland. Although most SATT and SACT species are abundant and not currently of conservation concern, human activities in the central Monte desert promote the structural simplification of the habitat, which could threaten future populations of Neotropical austral migrant landbirds in this ecosystem.

The “Freezing” of Science: Consequences of the Dogmatic Teaching of Ecology

In this article, we analyze some epistemological attributes of ecological hypotheses and theories and try to connect them with the need for teaching strategies that take into ac- count the strong provisional character of ecological knowl- edge. We submit that the dynamism of ecologys hypotheses and theories suggests that dogmatic teaching in this field is very likely to have negative effects on future ecology and ecologists. We accordingly try to show that critical thinking is an essential tool in both learning and practicing ecological science.

Artificial nest predation in natural and perturbed habitats of the central Monte Desert, Argentina

Abstract We examined nest predation rates at artificial nests in two contrasting habitats (open woodland and shrubland) inside the Reserve of Ñacuñán, west-central Argentina and in open woodlands within the reserve and a nearby grazed area, to assess whether between-habitat differences in vegetative structure were associated with changes in nest predation levels. We also quantified diurnal and nocturnal predation rates to further characterize the predator assemblage of the reserve. Nest predation rates and the estimated daily mortality rates were quite high in both open woodland and shrubland and did not differ significantly between them. Nest predation rate and daily mortality rate of nests in open woodlands of the reserve were high but similar to the rates for nests in adjacent grazed open woodlands. Nearly all predation events occurred during daylight hours. This result was not an artifact of the use of quail eggs because the proportion of depredated nests during the night was similar when we used smaller eggs of captive passerines. Our results support previous findings on the prevalence of birds as nest predators in this area. Avian predators seemed to be efficient at locating our artificial nests in all habitats, leading to the lack of differences between treatments. Conversely, our results suggest that extensive cattle grazing does not greatly modify nest predation risk for above-ground nests, although this conclusion is provisional given the conditions under which our experiments were carried out.

Behavioural flexibility does not prevent numerical declines of harvester ants under intense livestock grazing: Responses of harvester ants to habitat degradation

1. Human‐induced rapid environmental change may decrease food resources and create unfavourable conditions for native species. Organisms showing a flexible foraging behaviour can exploit novel or alternative foods and are more likely to persist, whereas less flexible organisms might suffer starvation and numerical reductions.

A Road Map for a Deontological Code for Geoscientists Dealing with Natural Hazards

Many professions have codes of conduct or deontological rules, but geoscientists dealing with natural hazards have been working on their own in the last decades not yet completing the task. A series of recent natural hazards that have hit the society in several parts of the world have made the call. Deontology is one of the main ethical decision-making approaches for driving actions leading to what is moral/ethically correct. To contribute with the construction of such a code, we present a road map to formulate this code based in the question-driven approach. Some considerations may be presented as guidelines: (a) it cannot be designed to the self-protection of the geoscientists but to safeguard society and the environment (even if it will contribute to); (b) it has to be constructed collectively; (c) it requires deep changes in educational systems, better preparing the citizens to deal with some scientific concepts. Without (c), (a) and (b) would not be enough. In addition, in constructing a geoethics code, we have to consider the three periods in the time-line of an extreme event: before, during, and after. Each period has particularities that will indicate different actions and conducts. Finally, the code, constructed collectively among practitioners, cannot be just a collection of “steps to be followed” but a real bridge between the moral consequences of being the privileged small part of the society who hold the scientific knowledge and the full society and the environment, for which we use to say we work for.