Jorge E. Schondube

Diet and the evolution of digestion and renal function in phyllostomid bats

Bat species in the monophyletic family Phyllostomidae feed on blood, insects, small vertebrates, nectar, fruit and complex omnivorous mixtures. We used nitrogen stable isotope ratios to characterize bat diets and adopted a phylogenetically informed approach to investigate the physiological changes that accompany evolutionary diet changes in phyllostomids. We found that nitrogen stable isotopes separated plant-eating from animal-eating species. The blood of the latter was enriched in (15)N. A recent phylogenetic hypothesis suggests that with the possible exception of carnivory, which may have evolved twice, all diets evolved only once from insectivory. The shift from insectivory to nectarivory and frugivory was accompanied by increased intestinal sucrase and maltase activity, decreased trehalase activity, and reduced relative medullary thickness of kidneys. The shift from insectivory to sanguinivory and carnivory resulted in reduced trehalase activity. Vampire bats are the only known vertebrates that do not exhibit intestinal maltase activity. We argue that these physiological changes are adaptive responses to evolutionary diet shifts.

Relationship between the presence of House Sparrows (Passer domesticus) and Neotropical bird community structure and diversity

Invasive exotic species pose an important threat to biodiversity worldwide. However, there is little information on the effects that specific exotic bird species have on native biota. The House Sparrow is an excellent ecological model to evaluate the effect that an invasive exotic species has on native bird communities. Our study describes the relationship of the presence and abundance of House Sparrows with the structure, diversity, and composition of native bird communities in West Mexico. We used two approaches to compare House Sparrow invaded and non-invaded bird communities: (1) at a small geographic-scale that allowed us to evaluate shifts in avian communities with presence of the House Sparrow under similar environmental conditions; and (2) at the landscape-level to evaluate the effect of this species under a scenario of greater environmental heterogeneity. Results from both approaches show that areas invaded by House Sparrows have heavily-dominated avian communities with low species richness, while non-invaded areas exhibit highly-even and species-rich bird communities. Species turnover analysis indicates that the decrease in the number of bird species in House Sparrow invaded areas is caused by species loss, rather than a shift in species composition. Our results indicate that the invasion of an area by the House Sparrow, through synergistic interactions with human activities, determines the composition, structure, and diversity of native bird communities.

The Cyanogenic Glycoside Amygdalin Does Not Deter Consumption of Ripe Fruit by Cedar Waxwings

Cyanogenic glycosides are common secondary compounds in ripe fruits that are dispersed by birds. These substances are toxic to some mammals. We examined the repellent effect of amygdalin, a cyanogenic glycoside, on Cedar Waxwings (Bombycilla cedrorum). Amygdalin did not reduce food ingestion in Cedar Waxwings, even at relatively high concentrations. In addition, these birds did not exhibit preference for amygdalin-free over amygdalin-containing fruit. Cedar Waxwings given artificial food that contained four times the amount of amygdalin found in some wild fruits ingested the equivalent of 5.5 times the oral lethal dose for rats in 4 h without exhibiting any external signs of toxicity. Amygdalin ingestion appeared to have a negative effect on nitrogen retention and food assimilation. However, when nitrogen retention and food assimilation were recalculated assuming that all amygdalin ingested was excreted intact, these negative effects disappeared. The presence of large amounts of unhydrolyzed amygdalin in the excreta of waxwings fed on amygdalin-laced food confirmed our conjecture that amygdalin was excreted intact. We hypothesize that in Cedar Waxwings, amygdalin is absorbed in the intestine but is not hydrolyzed by endogenous enzymes and thus is excreted intact in urine. The apparent lack of repellent effects of amygdalin in Cedar Waxwings suggest that toxicity data for rats and humans may be a poor predictor for the deterrent effect of fruit secondary compounds on frugivorous birds. Many hypotheses that have been posed to explain the presence of secondary compounds in ripe fruit assume that these substances have repellent/ toxic effects on avian seed dispersers. For some compounds, such as amygdalin and other cyanogenic glycosides, this assumption may not be valid.

Phyllostomid bat microbiome composition is associated to host phylogeny and feeding strategies

The members of the Phyllostomidae, the New-World leaf-nosed family of bats, show a remarkable evolutionary diversification of dietary strategies including insectivory, as the ancestral trait, followed by appearance of carnivory and plant-based diets such as nectarivory and frugivory. Here we explore the microbiome composition of different feeding specialists: insectivore Macrotus waterhousii, sanguivore Desmodus rotundus, nectarivores Leptonycteris yerbabuenae and Glossophaga soricina, and frugivores Carollia perspicillata and Artibeus jamaicensis. The V4 region of the 16S rRNA gene from three intestinal regions of three individuals per species was amplified and community composition and structure was analyzed with α and β diversity metrics. Bats with plant-based diets had low diversity microbiomes, whereas the sanguivore D. rotundus and insectivore M. waterhousii had the most diverse microbiomes. There were no significant differences in microbiome composition between different intestine regions within each individual. Plant-based feeders showed less specificity in their microbiome compositions, whereas animal-based specialists, although more diverse overall, showed a more clustered arrangement of their intestinal bacterial components. The main characteristics defining microbiome composition in phyllostomids were species and feeding strategy. This study shows how differences in feeding strategies contributed to the development of different intestinal microbiomes in Phyllostomidae.

Sugar and protein digestion in flowerpiercers and hummingbirds: a comparative test of adaptive convergence

Flowerpiercers are the most specialized nectar-feeding passerines in the Neotropics. They are nectar robbers that feed on the sucrose-rich diet of hummingbirds. To test the hypothesis that flowerpiercers have converged with hummingbirds in digestive traits, we compared the activity of intestinal enzymes and the gut nominal area of cinnamon-bellied flowerpiercers (Diglossa baritula) with those of eleven hummingbird species. We measured sucrase, maltase, and aminopeptidase-N activities. To provide a comparative context, we also compared flowerpiercers and hummingbirds with 29 species of passerines. We analyzed enzyme activity using both standard allometric analyses and phylogenetically independent contrasts. Both approaches revealed the same patterns. With the exception of sucrase activity, hummingbirds’ digestive traits were indistinguishable from those of passerines. Sucrase activity was ten times higher in hummingbirds than in passerines. Hummingbirds and passerines also differed in the relationship between intestinal maltase and sucrase activities. Maltase activity was two times higher per unit of sucrase activity in passerines than in hummingbirds. The sucrase activity of D. baritula was much lower than that of hummingbirds, and not unlike that expected for a passerine of its body mass. With the exception of aminopeptidase-N activity, the digestive traits of D. baritula were not different from those of other passerines.

Survival of Resident Neotropical Birds: Considerations for Sampling and Analysis Based on 20 Years of Bird-Banding Efforts in Mexico

ABSTRACT. Long-term bird-banding programs provide knowledge of the demographic rates of avian populations, but we currently lack information on demographic rates of most bird populations in species-rich tropical ecosystems. Banding in tropical regions is typically conducted with protracted or irregular sampling occasions that make the choice of the proper capture—mark—recapture (CMR) model difficult. Here, we address common challenges related to collecting and analyzing data to estimate survival rates of resident Neotropical birds using 20 years of banding efforts in Mexico as a case study. We applied Cormack-Jolly-Seber and Barker models to estimate apparent survival and recapture probabilities of species with sufficient data for survival analyses. We were able to analyze 6 resident species of 136 total species; apparent survival probabilities ranged from 0.30 to 0.77, and recapture probabilities from 0.11 to 0.52. For monitoring programs with existing data collected at continuous, uneven, or irregular intervals, we recommend the application of the Barker model over other models because it was more efficient in the use of available banding data and less often violated CMR assumptions. We recommend that monitoring programs last >10 years and provide additional protocol suggestions for primary and secondary sampling occasions, as well as the number of nets, potential net configurations, and the extent of the spatial scale. These baseline recommendations are likely to foster an increase in our knowledge of avian survival rates in tropical ecosystems, which is imperative for managing tropical bird populations under changing environmental conditions.

How do people perceive urban trees? Assessing likes and dislikes in relation to the trees of a city

Cities are systems that include natural and human-created components. When a city grows without proper planning, it tends to have low environmental quality. If improving environmental quality is intended, people’s opinion should be taken into account for a better acceptance of urban management decisions. In this study, we assessed people’s perception of trees by conducting a survey with a controlled sample of citizens from the city of Morelia (west-central Mexico). Citizens liked both native and exotic tree species and rejected mainly exotic ones. Preference for trees were related to tree attributes; such as size. Trees that dropped leaves or tended to fall were not liked. The most-mentioned tree-related benefits were oxygen supply and shade; the most mentioned tree-related damages were accidents and infrastructure damage. The majority of respondents preferred trees near houses to increase tree density. Also, most respondents preferred trees in green areas as well as close to their houses, as they consider that trees provide oxygen. The majority of the respondents thought more trees were needed in the city. In general, our results show that although people perceive that trees in urban areas can cause damages, they often show more interest for the benefits related to trees and consider there should be more trees in cities. We strongly suggest the development of studies that broaden our knowledge of citizen preferences in relation to urban vegetation, and that further policy making takes their perception into account when considering creating new urban green areas, regardless of their type or size.

Migrating to the City: Responses of Neotropical Migrant Bird Communities to Urbanization

Abstract. Birds that migrate to the neotropics have experienced dramatic population decreases over the last few decades. Although the transformation of their wintering habitats has been related to such decreases, several neotropical migrants are tolerant of human disturbances and winter in human-altered habitat. We surveyed a neotropical city broadly to evaluate how migrant birds respond to urbanization, finding that urbanization has a negative effect on communities of migrant birds: species richness and density of migrants decreased with urbanization. Although we recorded a significant decrease in the total number of individual neotropical migrants toward the center of the city, we found no differences among species when we assessed possible effects of the distance from the citys edge by species. Only tree cover had a positive significant relationship with both species richness and bird abundance. Our results show that urbanization can have an even greater negative effect on communities of neotropical migrant birds than for those of resident birds. However, some migrants that used the urban habitats we studied are of conservation concern, indicating that urbanization can act as a two-edged sword, affecting several migratory species negatively while offering winter habitats to others.

Effects of Sugar Composition and Concentration on Food Selection by Saussure's Long-nosed Bat (Leptonycteris curasoae) and the Long-tongued Bat (Glossophaga soricina)

Abstract In the Neotropics, bat-pollinated plants secrete relatively dilute nectars dominated by hexoses (glucose and fructose) with only small amounts of sucrose. We investigated the concentration and sugar composition preferences of Saussures long-nosed bat (Leptonycteris curasoae) and the long-tongued bat (Glossophaga soricina) to test the hypothesis that bats prefer the predominant characteristics (sugar composition and concentration) found in their natural diets. We offered bats pairs of test diets in large outdoor enclosures that allowed free flying. We used artificial nectars that simulated compositions and concentrations found in flowers visited by these 2 species at the study site. Contrary to our predictions, bats showed no preference between sugar types when test solutions had the same concentration. However, L. curasoae preferred concentrated over dilute solutions independent of sugar type. Only 1 preference for concentrated over dilute solutions was recorded for G. soricina. Both species of bat appeared to perceive sugar types as energetically equivalent in most trials. Our study rejects the hypothesis that nectar-feeding neotropical bats act as a selective pressure on nectar composition in chiropterophilous plants. Other possible explanations for the predominance of hexose in chiropterophilous flowers need to be evaluated.

The flowerpiercers' hook: an experimental test of an evolutionary trade-off.

The evolution of features that enhance an organisms performance in one activity can adversely affect its performance in another. We used an experimental approach to document a trade–off associated with the evolution of the long hook at the tip of the bill of birds belonging to the genus Diglossa (flowerpiercers). In Diglossa, the more derived flower–robbing nectarivorous species have maxillae (upper jaws) that terminate in enlarged curved hooks. The ancestral frugivorous species have maxillae with relatively small hooks. We mimicked bill evolution by clipping the terminal bill hook of nectarivorous Cinnamon–bellied Flowerpiercers (Diglossa baritula) to resemble the frugivorous condition. We found that birds with experimentally shortened bills ingested fruit more efficiently, but had a reduced ability to rob flowers. Birds with intact bills, by contrast, were good flower robbers but poor frugivores. The evolution of a hooked bill endowed flowerpiercers with the ability to efficiently pierce flowers and extract nectar, but hindered their efficiency to feed on fruit.