Predación post-dispersiva de semillas de malezas en un agroecosistema pampeano
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2017
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La predación es uno de los procesos que pueden causar pérdidas significativas de semillas, tanto en los bancos epigeos como en los hipogeos. En este trabajo se evalúan las pérdidas del banco superficial de semillas, de tres especies de malezas, ocasionadas por la predación producida por insectos, roedores y aves en un área de clausura con alta cobertura vegetal y en el área agrícola adyacente, durante el período otoñal 2015 y 2016. El estudio se realizó en el Campo Experimental J. F. Villarino (FAC-UNR), ubicado en la localidad de Zavalla S. F. Argentina (33º 01' lat. S). Se seleccionó un área de 3,12 ha, que comprende un espacio de 250x100 m de lote agrícola en período de barbecho, proveniente de monocultivo de soja sembrado bajo el sistema de siembra directa y un espacio adyacente de 250x25 m que corresponden a un área de clausura, donde no se realizan actividades agrícolas desde hace 31 años. Se localizaron 5 transectas, desde la clausura hasta el área de barbechos, distantes a 25 m unas de otras. En cada transecta se dispusieron 4 estaciones de muestreo ubicadas una en la clausura, otra en el borde y dos en el lote agrícola. En cada estación se colocaron al nivel de la superficie del suelo, cuatro bandejas plásticas de 18x11x2,5 cm, donde se colocaron 100 semillas de Commelia erecta, Echinochloa colona y Chenopodium album. Cada bandeja representa un tratamiento de predación y en su superfice se colocaron alambres tejidos de distintas tramas y con distinta arquitectura, de manera que puedan aislarse los factores de predación: total (TOT), insectos y roedores (I&R), sólo insectos (INS) y sin predación (SPR). Con los datos obtenidos se calculó la tasa de predación diaria de semillas: P=100 (1 - r 1/t). Para establecer la presencia y cuatificar la abundancia de predadores de semillas se utilizaron trampas "pitfall" para insectos, trampas Tomahawk para roedores y observación directa para aves. En las evaluaciones de insectos no se detectaron diferencias en la abundancia, riqueza, diversidad entre los distintos ambientes relevados; no obstante, la abundancia de detritívoros fue mayor en el rastrojo, la abundancia y riqueza de hormigas fue mayor en la clausura y la abundancia de predadores fue mayor en el área de borde. La abundancia, riqueza, diversidad y equitatividad de los roedores no difirieron entre ambos años de muestreo y tampoco entre fechas de muestreos dentro de cada año. El 49 por ciento de los roedores registrados corresponde a Cavia aperea y el 33 por ciento a Calomys musculinus, esta última es una especie reconocida por alimentarse de semillas de malezas. La abundancia de roedores fue mayor en la clausura respecto al rastrojo de soja; el borde presentó una situación intermedia. El 41 por ciento de los registros de aves corresponde a Passer domesticus y el 33 por ciento a Zenaida auriculata, especies cuya principal fuente de alimentación son las semillas. La abundancia de aves predadoras de semillas es mayor en las áreas de rastrojos y la riqueza es menor en la clausura. La diversidad y la equitatividad no difieren entre ambientes. La predación de semillas de malezas fue muy variable, las especies más predadas fueron E. colona en el 2015 y C. album en 2016. Los mayores predadores fueron los insectos y los roedores. Prácticas más respetuosas y sostenibles con el medio ambiente, como la promoción de la predación de semillas mediante el mantenimiento e incremento de los agentes biológicos de predación, podrían contribuir a la disminución de las aplicaciones de herbicidas en los agroecosistemas pampeanos, aunque esto requiere más investigación.
The seed predation is one of the processes than can cause significant losses of seeds, both in epigeal and hypogeal banks. In this work was evaluate the losses of the superficial bank of deeds, of three species of weeds, caused by the predation produced by insects, rodents and birds in a closure area with high vegetation covedr and in the adjacent agricultural area, during the Autumnal period 2015 and 2016. The study was carried out in the J. F. Villarino Experimental Field (FCA-UNR), located in the town of Zavalla, S. F. Argentine (33º 01' lat. S). It's selected an area of 3.12 has, comprising a space of 250 x 100 m of an agricultural lot in the fallow period, from a monoculture of soybeans planted under the direct sowing system and adjacent space of 250 x 25 m that corresponds a closure area where not agricultural activities have been carried out for 31 years. Five transects were located, from the closure of the fallow area, 25 m away from each other. In each transect, ther were 4 light stations located one in the closure, another in the edge and two in the agricultural lot. In each station, four plastic trays of 18 x 11 x 2.5 cm palced at the level of the ground surface, where 100 seeds of Commelina erecta, Echinochloa colona and Chenopodium album were placed. Each tray represents a predation tratment and on its surface, they are placed in elastics of the same type as insects (TOT), insects and rodents (I&R), only insectos (INS) and without predation (SPR). With the daata obtained, the daily seed predation rate was calculated: P=100 (1 - r 1/t). To establish the presence and quantify the abundance of seed predators in the trap for insects, Tomahawk traps for rodents and direct observation for birds. In the evaluations of insects no differences in abundance, richness, diversity are detected between the different environments surveyed; nevertheless, the abundance of detritus in the stubble, the abundance, and abundance of ants was grater in the closure and the abundance of predator was greater in the edge area. The abundance, richness, diversity, and equitability of the rodents did not differ between years and between dates within each year. To another hand, the 49 per cent of rodents captured was Cavia aperea and 33 per cent to Calomys musculinus, this last one, is a sepecies recognizes by feeding of weeds. The abundance of rodents was grater in the closure with respect to the stubble of soybean; the edge presented an intermediate situation. The 41 per cent of bird records correspond to Passer domesticus and 33 per cent to Zenadia auriculata, which mostly consumes the main source of food. The abundance of predatory seed birds is grater in the stubble areas and the richness is lower in the closure. Diversity and equity do not differ between environments. The depredation of weed seeds was very variable; the mos depredated seed was E. colona in 2015 and C. album in 2016. The main predators were insects and rodents. More respectful and sustainable practices with the environment, such as the promotion of the prevention of seeds through the maintenance and increase of biological predation agents, which may contribute to the reduction of herbicide applications in the Pampean agroecosystems, although this it requires more investigation.
The seed predation is one of the processes than can cause significant losses of seeds, both in epigeal and hypogeal banks. In this work was evaluate the losses of the superficial bank of deeds, of three species of weeds, caused by the predation produced by insects, rodents and birds in a closure area with high vegetation covedr and in the adjacent agricultural area, during the Autumnal period 2015 and 2016. The study was carried out in the J. F. Villarino Experimental Field (FCA-UNR), located in the town of Zavalla, S. F. Argentine (33º 01' lat. S). It's selected an area of 3.12 has, comprising a space of 250 x 100 m of an agricultural lot in the fallow period, from a monoculture of soybeans planted under the direct sowing system and adjacent space of 250 x 25 m that corresponds a closure area where not agricultural activities have been carried out for 31 years. Five transects were located, from the closure of the fallow area, 25 m away from each other. In each transect, ther were 4 light stations located one in the closure, another in the edge and two in the agricultural lot. In each station, four plastic trays of 18 x 11 x 2.5 cm palced at the level of the ground surface, where 100 seeds of Commelina erecta, Echinochloa colona and Chenopodium album were placed. Each tray represents a predation tratment and on its surface, they are placed in elastics of the same type as insects (TOT), insects and rodents (I&R), only insectos (INS) and without predation (SPR). With the daata obtained, the daily seed predation rate was calculated: P=100 (1 - r 1/t). To establish the presence and quantify the abundance of seed predators in the trap for insects, Tomahawk traps for rodents and direct observation for birds. In the evaluations of insects no differences in abundance, richness, diversity are detected between the different environments surveyed; nevertheless, the abundance of detritus in the stubble, the abundance, and abundance of ants was grater in the closure and the abundance of predator was greater in the edge area. The abundance, richness, diversity, and equitability of the rodents did not differ between years and between dates within each year. To another hand, the 49 per cent of rodents captured was Cavia aperea and 33 per cent to Calomys musculinus, this last one, is a sepecies recognizes by feeding of weeds. The abundance of rodents was grater in the closure with respect to the stubble of soybean; the edge presented an intermediate situation. The 41 per cent of bird records correspond to Passer domesticus and 33 per cent to Zenadia auriculata, which mostly consumes the main source of food. The abundance of predatory seed birds is grater in the stubble areas and the richness is lower in the closure. Diversity and equity do not differ between environments. The depredation of weed seeds was very variable; the mos depredated seed was E. colona in 2015 and C. album in 2016. The main predators were insects and rodents. More respectful and sustainable practices with the environment, such as the promotion of the prevention of seeds through the maintenance and increase of biological predation agents, which may contribute to the reduction of herbicide applications in the Pampean agroecosystems, although this it requires more investigation.
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Agroecosistemas, Insectos depredadores, Pájaros depredadores, Roedores, Semillas, Malezas, Zavalla (Argentina)