Tamaño poblacional y alimentación de la nutria de río (lontra longicaudis annectens) en la Costa de Oaxaca, México

The neotropical river otter (Lontra longicaudis annectens) is threatened in Mexico, and in order to design sound conservation strategies for its conservation, basic studies on their biology and ecology are necessary. The diet and abundance were evaluated between July, 1999 and August, 2000 in the rivers Ayuta, Copalita and Zimatán in the coast of Oaxaca. We considered estimated of four otters in 147.5 km the river Ayuta. 86 otters in 330.75 km the rive Copalita and 177 otters in 228.85 km the river Zimatán.We found a relation in an indirect way between the abundance of the otter and dissolved O2. From 330 scats it was determined that they use four prey categories, which include crustaceans (53.0 ± 3.6%), fish (33.1 ± 9.9%), insects (9.8 ± 7.6%) and amphibians (4.0 ± 3.3%). In relation to the biomass ingested, the main prey were Macrobrachium americanum, M. acanthochirus and Gobiexos mexicanus. The largest number of fish and crustaceans used was obtained in the river Zimatán (n = 258 samples, 16 spp.) followed by the river Ayuta (n = 253, 14 spp) and the river Copalita (n = 197, 16 spp). We found a relation among the frequency of appearance of prey species in the scats, with their abundance (p < 0.01; r2 = 0.40), as well as a significant relation between the consumed biomass and the abundance of the prey. Abundance of prey is determined by O2 dissolved in the water (p = 0.04; r2 = 0.09) as well as turbidity (p = 0.04; r2 = 0.22). There was no relation between the physiochemical variables of the water with the diversity of the potential prey.La nutria de río neotropical (Lontra longicaudis annectens) se encuentra amenazada en México y para diseñar estrategias reales de conservación, son necesarios estudios básicos de su biología yecología. Se evaluaron la dieta y abundancia entre julio de 1999 y agosto del 2000 en los ríos Ayuta, Copalita y Zimatán en la costa de Oaxaca. Considerando una estimación de cuatro nutrias en 147.5 kmdel río Ayuta. 86 nutrias en 330.75 km del río Copalita y 177 nutrias en 228. 85 km del río Zimatán. Encontrando de forma indirecta una relación entre la abundancia de la nutria y el O2 disuelto en el agua.De 330 excretas se determinaron cuatro categorías de presa que incluyen crustáceos (53.0 ± 3.6%), peces (33.1 ± 9.9%), insectos (9.8 ± 7.6%) y anfibios (4.0 ± 3.3%). Respecto a la biomasa consumida, la presa principal fue Macrobrachium americanum, M. acanthochirus y Gobiexos mexicanus. El número más alto de peces y crustáceos se obtuvo en el río Zimatán (n = 258 muestras, 16 spp.) seguido por el río Ayuta (n = 253, 14 spp) y el río Copalita (n = 197, 16 spp). Encontrando una relación entre la frecuencia de aparición de especies de la presa en las excretas, con su abundancia (p < 0.01; r2 = 0.40), así como una relación significativa entre la biomasa consumida y la abundancia de las presas. La abundancia de las presas está determinada por O2 disuelto en el agua (p = 0.04; r2 = 0.09) así como la turbiedad (p = 0.04; r2 = 0.22). No hubo ninguna relación entre las variables fisicoquímicas del agua con la diversidad de las presas potenciales

Is species richness driving intra- and interspecific interactions and temporal activity overlap of a hantavirus host? An experimental test

<div><p>High species diversity of the potential animal host community for a zoonotic pathogen may reduce pathogen transmission among the most competent host, a phenomenon called the “dilution effect”, but the mechanisms driving this effect have been little studied. One proposed mechanism is “encounter reduction” where host species of low-competency decrease contact rates between infected and susceptible competent hosts, especially in directly transmitted diseases. We conducted an experiment in outdoor enclosures in northwestern Mexico where we manipulated rodent assemblages to assess the effect of species richness on the frequency of intra- and interspecific interactions and activity patterns of a hantavirus reservoir host (North American deermouse; <i>Peromyscus maniculatus</i>). Trials consisted of three treatments of rodent assemblages that differed in species richness, but had equal abundance of deermice; treatment 1 consisted of only deermice, treatment 2 included deermice and one non-competent host species, and treatment 3 included two non-competent host species in addition to deermice. To measure interactions and temporal activity, we strategically deployed foraging stations and infrared cameras. We did not find differences in the frequency of intraspecific interactions of deermice among treatments, but there were significantly more interspecific interactions between deermouse and non-competent hosts in treatment 2 than treatment 3, which is explained by the identity of the non-competent host species. In addition, there were differences in activity patterns between rodent species, and also between deermice from treatment 1 and treatment 2. These results indicate that at least at a small-scale analysis, the co-occurrence with other species in the study area does not influence the frequency of intraspecific interactions of deermice, and that deermice may be changing their activity patterns to avoid a particular non-competent host species (<i>Dipodomys merriami</i>). In conclusion, in this deermouse-hantavirus system a potential dilution effect would not be through intraspecific encounter reduction in the most competent hantavirus host. To identify variables of host assemblages that can influence pathogen transmission, we highlight the need to address the identity of species and the composition of assemblages, not only host species richness or diversity.</p></div

Results of ROSARIO algorithm null model analyses of temporal niche overlap (both seasons combined).

<p>Overlap was quantified as the average of all pair-wise overlap values calculated via the Czechanowski index, using the numbers of records for each species at two time intervals (30 min and 1 h). P-values are two-tailed probabilities of finding non-random assemblage-wide temporal niche overlap. Tail (T) indicates that empirical overlap occurs on the right-hand (R) side of the simulated distribution. Values in the extreme right indicate coincident activity patterns. Values on the extreme left would have indicated segregated activities. Significant results in bold. Results of temporal niche overlap separated by season are provided in <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0188060#pone.0188060.s002" target="_blank">S2 Table</a>.</p

Diagrams of enclosures and experimental design.

<p>(A) Diagram of an enclosure with the camera trap array. (B) Diagram of the experimental design. Each column has the number of individuals (M = male, F = female), species richness, and species diversity of each treatment.</p

Diel activity patterns of deermice in each treatment (T).

<p>(a) samples from late winter, and (b) samples from spring. Bars indicate the proportion of independent records taken at that time of the day. Tick lines represent the mean vector and its circular standard deviation.</p