Tracking Nutrient Routing in Avian Consumers in a Subtropical Desert

Abstract

The nutrients animals ingest are allocated to serve different functions. We used contrasting C stable isotope signatures of dominant vegetation types in a North American subtropical desert to decipher how avian consumers allocate nutrients to fuel oxidative metabolism and to construct tissues. We conducted C stable isotope analysis of breath and feathers collected from nectarivores (hummingbirds) and of breath, plasma, and red blood cell samples collected from frugivores, granivores, and insectivores. Based on varying nutrient characteristics of food sources, we expected that for frugivores and granivores, CAM-derived food (RC CAM ) would have similar importance for oxidative metabolism and for tissue building, that RC CAM in nectarivores and insectivores would be more important for fueling metabolism than for generating tissues, and that (although low) RC CAM in insectivores would be higher for sustaining metabolism than for building tissues. Our predictions held true for nectarivores and granivores, but RC CAM use in tissue building was lower than expected in frugivores and higher than expected in insectivores. Our examination at the trophic guild, population, and individual levels showed that in general, nutrients used to sustain oxidative metabolism and tissue construction had a uniform isotopic origin. This finding suggests that the avian community under investigation does not route different food groups to fulfill different needs. However, we found some exceptions, indicating that birds can use different food sources for different functions, irrespective of trophic guild.Abstract in Spanish is available with online material.

Columnar cacti as sources of energy and protein for frugivorous bats in a semi‐arid ecosystem

“…It is interesting to note that fruit‐eating birds in the area do not feed on CAM fruits to a large extent (Herrera et al . , ), similarly to frugivorous bats. Our study thus confirms that nutrients derived from columnar cactus forests do not cascade equally into all members of the vertebrate community and that its importance might be limited to some functional groups (Herrera et al .…”

“…Our study thus confirms that nutrients derived from columnar cactus forests do not cascade equally into all members of the vertebrate community and that its importance might be limited to some functional groups (Herrera et al . , , Orr et al . ).…”

Dietary importance of C3 and CAM food pathways for birds in a Neotropical semiarid zone

“…Even though CAM plants ( e.g ., cacti and agaves) are important elements of the communities in the system we studied (Nassar et al, 2003; Smith & Rivero, 1991), their use as food did not permeate equally among avian consumers. Similarly to subtropical semiarid ecosystems (Herrera Montalvo & Osorio M, 2016; Herrera Montalvo et al, 2013), use of CAM‐derived food was mainly restricted to some plant‐eating and omnivorous bird species. Use of CAM food by these species corresponds to findings of previous work in South American dry ecosystems using other methods to determine diet (Lemus, 2003; Marín‐Espinoza & Durán‐Mata, 1994; Nassar & Ramírez, 2004; Silvius, 1995; Soriano et al, 1999).…”

“…The output of the MixSiar model produces a range of solutions regarding the proportional contribution of each food to the diet per species, of which we present the mean ± SD and the 95% CI. We categorized the contribution mean values as high (≥0.67), intermediate (0.34 to 0.66), or low (≤0.33) for descriptive purposes (Herrera M & Osorio M, 2016).…”

“…Recent studies have taken advantage of the isotopic mosaic represented by vegetation with contrasting photosynthetic pathways to unveil their importance for the nutrition of vertebrate consumers in North American subtropical dry ecosystems (Herrera Montalvo & Osorio M, 2016; Herrera Montalvo, Rodríguez Galindo, & Ibarra López, 2013). In particular, patterns in the stable isotope composition of carbon ( 13 C and 12 C) allow tracking the nutritional importance of plants with different photosynthetic pathways (e.g., C3—Calvin cycle, C4—dicarboxylic acid, and Crassulacean acid metabolism pathways) because they have contrasting isotopic values (Ehleringer & Monson, 1993; Sala & Aguiar, 1996).…”