جستجوی مقالات مرتبط با کلیدواژه « تغییرات جمعیت » در نشریات گروه « اکولوژی »

Leeches as one of the most important components of the aquatic ecosystem has gained so much attention. Due to their parasitism, they are commercially considered as dangerous factor in fishery and biologically as potential indexes for chemical pollutant in aquatic ecosystems. So their identification and population dynamics in different aquatic habitats would be valuable. Species diversity of fresh water leeches in three rivers in east of Tehran province, Lar, Jajrood and Hablehrood rivers, were studies through 6 months in 2015. During the sampling procedure from 10 station in 3 rivers, two species, Placobdella costata and Erpobdella octaculata were collected which the latter was more frequent in all the sampling points. Study on population dynamics of Erpobdella octaculata showed no significant difference among different sampling points; however, population in different sampling months showed significant difference and the most collected samples belonged to May; it was assumed that the highest population in May would be due to the higher population of their host Ephemeroptera, favorite temperature of water and low level of chemical pollutants.

Syrphids are one of the most important natural enemies of wheat aphids. Larvae feed in aphid colonies and reduce the population. To identify these predators and their population fluctuation during wheat growing season، five fields with area about one ha were selected. Syrphids were swept weekly by standard insect net in the selected fields. The result showed that 14 species of flower flies occur in the wheat field of Kurdistan province which among them Eupeodes corollae with %52. 41of total population in 2002 and %47. 65 in 2003 has the highest frequency. Among predator species، Eupeodes nuba، Sphaerophoria scripta، S. turkmenicaand Eupeodes corollae constitute the largest part of syrphid population. Seven species of aphids were identified and their population changes were measured by weekly random sampling of 40 plants. Sitibion avenae and Schizaphis graminum were dominant aphid species where their frequency were measured as %66 and %30of total specimens in 2001 and %69. 5 and %25 of total specimens in 2002 respectively. The positive correlation between aphid population increase and emergence of syrphid larvae was discussed briefly.