The introduced silver Pheasant (Lophura Nycthemera) in Patagonia Abundance, group structure, activity patterns and association to human disturbance

Los fasiánidos son uno de los grupos de aves introducidas con mayor impacto en los ecosistemas nativos. En la Patagonia varias especies de fasiánidos están establecidas o en proceso de establecimiento, por lo que es relevante conocer sus impactos sobre los ecosistemas. El Faisán Plateado (Lophura nycthemera) fue introducido en Isla Victoria en la década de 1950 y se estableció exitosamente en toda la isla. El objetivo de este trabajo es estudiar la población de esta especie en Isla Victoria en términos de abundancia y su asociación con el disturbio humano como un primer paso para conocer su impacto potencial en el ecosistema. Se realizaron capturas fotográficas mediante fototrampeo y observaciones directas en transectas lineales ubicadas en áreas con niveles alto y bajo de disturbio humano. Con los datos de las capturas fotográficas se estimó un índice de abundancia relativa para comparar el uso de hábitat entre las dos áreas. Se utilizó la técnica de muestreo a distancia para estimar la densidad poblacional a partir de las observaciones directas. El Faisán Plateado usó más las áreas con un alto nivel de disturbio, lo que sugiere que la presencia de hábitats modificados podría facilitar su establecimiento y dispersión en la Patagonia. Las densidades poblacionales, tanto en las áreas con alto como con bajo nivel de disturbio, fueron mayores que las reportadas en su área de distribución nativa, mostrando que esta especie ha tenido un gran éxito en Isla Victoria. La alta abundancia, junto con características distintivas tales como el gran tamaño, los hábitos de alimentación y el comportamiento social, pueden moldear las interacciones con las especies nativas e influenciar su impacto sobre las comunidades nativas.Phasianids are one of the groups of introduced birds with highest impact on native ecosystems. In Patagonia several phasianids are established or in process of establishment, thus it is relevant to know their impacts on ecosystems. The Silver Pheasant (Lophura nycthemera) was introduced to Isla Victoria in the 1950’s and successfully established all over the island. The aim of this work is to study the population of this species on Isla Victoria in terms of abundance and association to human disturbance as a first step to know its potential impact in the ecosystem. We conducted camera-trapping and direct observations in linear transects located in highly disturbed and in lowly disturbed areas. Using camera-trapping data we estimated an index of relative abundance to compare habitat use between areas. We used the distance-sampling approach to estimate population density with the data from direct observations. The Silver Pheasant used much more frequently areas with a high level of disturbance, suggesting that the presence of disturbed habitats could facilitate establishment and spread of this species in Patagonia. Population densities in areas with high and with low levels of disturbance were higher than those reported from the native distribution area, showing that the Silver Pheasant had a great success on Isla Victoria. The high abundance, together with distinctive characteristics such as a large body size, foraging habits and social behaviour can shape the interactions with native species and influence its impact on native communities

Replacement of native by non-native animal communities assisted by human introduction and management on Isla Victoria, Nahuel Huapi National Park

One of the possible consequences of biological invasions is the decrease of native species abundances or their replacement by non-native species. In Andean Patagonia, southern Argentina and Chile, many non-native animals have been introduced and are currently spreading. On Isla Victoria, Nahuel Huapi National Park, many non-native vertebrates were introduced ca. 1937. Records indicate that several native vertebrates were present before these species were introduced. We hypothesize that seven decades after the introduction of non-native species and without appropriate management to maintain native diversity, non-native vertebrates have displaced native species (given the known invasiveness and impacts of some of the introduced species). We conducted direct censuses in linear transects 500 m long (n = 10) in parallel with camera-trapping (1,253 camera-days) surveys in two regions of the island with different levels of disturbance: high (n = 4) and low (n = 6) to study the community of terrestrial mammals and birds and the relative abundances of native and non-native species. Results show that currently non-native species are dominant across all environments; 60.4% of census records and 99.7% of camera trapping records are of non-native animals. We detected no native large mammals; the assemblage of large vertebrates consisted of five non-native mammals and one non-native bird. Native species detected were one small mammal and one small bird. Species with the highest trapping rate were red and fallow deer, wild boar, silver pheasant (all four species are non-native) and chucao (a native bird). These results suggest that native species are being displaced by non-natives and are currently in very low numbers

The introduced Silver Pheasant (Lophura nycthemera) in Patagonia: abundance, group structure, activity patterns and association to human disturbance

Phasianids are one of the groups of introduced birds with highest impact on native ecosystems. In Patagonia several phasianids are established or in process of establishment, thus it is relevant to know their impacts on ecosystems. The Silver Pheasant (Lophura nycthemera) was introduced to Isla Victoria in the 1950’s and successfully established all over the island. The aim of this work is to study the population of this species on Isla Victoria in terms of abundance and association to human disturbance as a first step to know its potential impact in the ecosystem. We conducted camera-trapping and direct observations in linear transects located in highly disturbed and in lowly disturbed areas. Using camera-trapping data we estimated an index of relative abundance to compare habitat use between areas. We used the distance-sampling approach to estimate population density with the data from direct observations. The Silver Pheasant used much more frequently areas with a high level of disturbance, suggesting that the presence of disturbed habitats could facilitate establishment and spread of this species in Patagonia. Population densities in areas with high and with low levels of disturbance were higher than those reported from the native distribution area, showing that the Silver Pheasant had a great success on Isla Victoria. The high abundance, together with distinctive characteristics such as a large body size, foraging habits and social behaviour can shape the interactions with native species and influence its impact on native communities.</jats:p

Naturalized and studied number of species in each region.

<p>Number of naturalized species (black bars) and of studied species (grey bars) in the nine regions considered. Numbers between parentheses indicate the number of articles analyzed.</p

Negative and positive impacts of the few bird species with reported benefits in the bibliography.

<p>Table showing the negative and positive impacts for all species with reported benefits in the bibliography. The scores obtained for negative impacts based on the impact scale are given and positive impacts are described.</p><p>Negative and positive impacts of the few bird species with reported benefits in the bibliography.</p

Relation between mean impact score by category and mean residence time.

<p>Points represent the mean values and error bars the standard error. This graph shows only the four categories that have at least seven data points.</p

Impacts of avian families on natural ecosystems.

<p>Bars represent global impacts of the family and black points the average impact of the family. Only families with reported impacts are shown. Categories “chemical, physical or structural impact on the ecosystem”, “grazing/herbivory/browsing”, and “interaction with other non-native species”, are abbreviated to “physical impacts”, “grazing”, and “interactions”, respectively.</p

Relation between known impact of a species and its residence time.

<p>Each point represents the event of introduction of one species to one region of the world. Multiple R-squared: 3.30e-05, Adjusted R-squared: -0.02, p = 0.97.</p

Relation between mean impact value and the number of studies conducted for every impact category.

<p>Number of studies conducted for every impact category (x axis) and the corresponding impact mean (y axis). Bars represent the standard error. Vertical and horizontal lines are located at the mean of x and y axes respectively and separate points in four quadrants according to the relative number of studies and the level of impact. Categories “chemical, physical or structural impact on the ecosystem”, “grazing/herbivory/browsing”, and “interaction with other non-native species”, are abbreviated to “physical impacts”, “grazing”, and “interactions”, respectively.</p