Published in December 2012
Research articles
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Anindita Chatterjee and Anjana Dewanji
Peroxidase as a metric of stress tolerance and invasive potential of alligator weed (Alternanthera philoxeroides) growing in aquatic habitats (pp 65-76) |
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An attempt was made to understand the potential of Alternanthera philoxeroides, alligator weed to adapt to diverse conditions present in pond ecosystems,
through a correlative investigation of its natural growth pattern and peroxidase level. Eleven ponds were graded into two subjective categories:
“A. philoxeroides Infestation” (High, Medium, Low) and “Level of Pollution” (High and Low), to test for difference in mean peroxidase concentration
in A. philoxeroides populations. Significant changes in mean peroxidase concentration in A. philoxeroides were found in ponds categorized
on the basis of level of pollution, indicating the adaptability of this plant to propagate under pollution stress. On the other hand, there was no significant
change in mean peroxidase concentration for plants growing in ponds categorized on the basis of infestation showed that dense, vegetative proliferation caused
no stress in A. philoxeroides. An efficient method of assaying peroxidase in A. philoxeroides, under field conditions, using the best suited leaf
group (Tips, Tips + 1st leaf pair”, 2nd leaf pair) was also explored. “Tips + 1st leaf pair” proved to be a better sample than mature leaves for estimation
of peroxidase concentration in A. philoxeroides.
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Matthew Tenywa Mwanja, Wilson Waiswa Mwanja, Vincent Muwanika, Charles Masembe and Sylvester Nyakaana
Genetic evidence of successful establishment of the Nile perch (Lates spp. L.) in East African lakes and implications for management (pp 77-88) |
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Nile perch establishment in novel ranges in East Africa is one of the most successful freshwater invasion stories in the recent history.
It became ecologically dominant and well established in several lakes in the Lake Victoria Region in a period of less than 5 decades.
Genetic diversity of both introduced and native populations were assessed and patterns compared in order to establish the genetic consequences
of their introductions. Genetic variation was surveyed at both the mitochondrial control region (CR) and at nine microsatellite loci.
A total of 527 Nile perch fish were sampled from 5 East African lakes: native source populations were examined from lakes Albert and Turkana
while introduced populations were sampled from lakes Kyoga, Nabugabo and Victoria. Both types of markers revealed higher average genetic diversity
for invasive species (HE = 0.70, h = 0.81) than for native source populations (HE = 0.66, h = 0.69). Both populations scored relatively higher
than the average for freshwater fishes (HE = 0.62). Both native and introduced populations had 2 underlying genetic groupings in similar proportions
as revealed by the STRUCTURE program. The high genetic diversity was most probably a consequence of higher numbers of propagules than outlined by official
records of introductions. Use of high number of individuals at stocking is probably the reason for apparently minimized ‘founder effects’ of Nile perch
in the introduced ranges. The two underling populations revealed through genetic analysis may be representatives of the two subspecies of Nile perch
previously reported in other studies. Implications to the management of this fishery in the East African region is that with the relatively high genetic
diversity, the species could be sustainably exploited if it were effectively managed. In addition, further studies of the life histories and other attributes
of the two genetic groupings of Nile perch in the region are recommended, as they may require different management plans.
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M. Nikki Grant-Hoffman, Amanda Clements, Anna Lincoln and James Dollerschell
Crested wheatgrass (Agropyron cristatum) seedings in Western Colorado: what can we learn? (pp 89-96) |
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Non-native species have been widely transported, becoming components of ecosystems worldwide. In some cases this can change the structure and function of an ecosystem.
Crested wheatgrass (Agropyron cristatum, Agropyron spp.) was introduced into the Western U.S. in the late 18th and early 19th centuries. Since introduction,
it has been planted in western rangelands currently occupying millions of acres. Crested wheatgrass causes significant changes in areas where it dominates the vegetation,
and restoring rangelands planted with crested wheatgrass to higher plant diversity and ecosystem function has been met with limited success. Here we revisit historical
frequency monitoring data collected in western Colorado on public lands that were planted with crested wheatgrass between 1940 and 1980. We also monitored vegetation
before and after mechanical treatment (removal of vegetation with the use of a dixie harrow pulled behind a tractor) and re-seeding of desirable species in three areas
dominated by crested wheatgrass. We looked for increasing or decreasing trends in plant species, and for plant species that persist with crested wheatgrass. We found that
crested wheatgrass increased significantly (p=0.09) over time, we also found five species of grasses, two shrub species, and one forb species that were persistent in areas
planted with crested wheatgrass. We found that in mechanically treated areas, the only significant trend was a reduction of native grasses (p<0.05). Our findings suggest
that in areas planted with crested wheatgrass, frequency of crested wheatgrass can increase over time. Further, mechanical treatments coupled with seeding were not effective
at reducing crested wheatgrass cover, or at increasing native and desirable species. These sites may have experienced a shift to a stable state.
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Cristina Sanhueza and Sergio M. Zalba
Experimental control of Spanish broom (Spartium junceum) invading natural grasslands (pp 97-104) |
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A group of legumes generically known as brooms are among the most successful shrubs invading grasslands in South America and other regions.
These species share a set of biological features that enhance their invasiveness, such as abundant and long-lasting seed banks, aggressive
root systems and rapid growth, combined with their ability for re-sprouting after cutting or burning and for avoiding herbivores. They grow
in dense stands that exclude native vegetation and are able to change ecological processes, increasing fire frequency and intensity, and fixing
atmospheric nitrogen. The Spanish broom (Spartium junceum) is a shrub native form the Mediterranean that was introduced into the Argentine
Pampas grasslands where it spreads over remnants of pristine ecosystems, threatening their biodiversity. This paper reports the results obtained
after an adaptive management strategy aimed at controlling this species in a nature reserve, and compares the efficiency of different mechanical
and chemical control techniques in terms of the number of plants killed and the effects on surrounding vegetation and on the recruitment of broom
seedlings. Control was implemented in two phases, the first included three treatments: i) cut at the base of the plant, ii) cut followed by the immediate
application of Togar (Picloram 3% + Triclopyr 6%, at a 5% dilution in diesel oil) on top of the cut stump, and iii) foliar spraying with Togar. The follow-up
treatments, implemented one year later, consisted of spraying the re-sprouts with Togar (5% in diesel oil) or Glyphosate 36% (2% in water). The best option
in terms of controlling Spanish broom was spraying the re-sprouts with Togar which gave 100% mortality of the treated plants, compared with values of 40% - 100%
re-sprouting for the other options tested. None of the methods was associated with an increase in seedling recruitment, nor with significant changes in the vegetation
in the immediate vicinity of the controlled brooms.
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Samuel Getachew, Sebsebe Demissew and Tadesse Woldemariam
Allelopathic effects of the invasive Prosopis juliflora (Sw.) DC. on selected native plant species in Middle Awash, Southern Afar Rift of Ethiopia (pp 105-114) |
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The allelopathic effects of the invasive Prosopis juliflora (Sw.) DC. was studied on seed germination and seedling growth of Acacia nilotica (L.)
Willd. ex Del., Acacia tortilis (Forssk.) Hayne, Cenchrus ciliaris L. and Enteropogon rupestris (J.A. Schmidt) A. Chev. Vegetation sampling
in different habitat types in the area was made to identify the target plant species. Comparison of canopy characteristics among P. juliflora, A. nilotica
and A. tortilis was also made to observe differences if any in canopy closure. P. juliflora was recorded in all habitat types in highest density and
observed affecting the plant diversity there in. Its growth characteristics and dense thicket formation restrict light to the ground flora and hence diminishes plant
diversity. Leaf, bark and root aqueous extract of P. juliflora at 0, 0.5, 0.8, 1, 2 and 6% were prepared and their effect studied on germination percentage
and seedling growth of the study plant species. Germination of A. nilotica and A. tortilis was not affected by all aqueous extracts of different organ
parts of P. juliflora while leaf and root extracts at higher concentrations inhibited germination of C. ciliaris and E. rupestris. Shoot and root
growth of the study species were inhibited by leaf and root at higher concentrations. Seed germination of all species except A. nilotica was inhibited by soil
amended with decaying plant parts and under canopy soil. The effect is species specific and annuals (grasses and herbs) were affected more than perennials. Leaf seems
to contain greater number/amount of inhibitors than does root and bark. Bark seems to contain the least. Heavy accumulation of toxic substances at under canopy soil
of P. juliflora may be one of the reasons for its invasiveness and low plant diversity.
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Deniz Innal
Alien fish species in reservoir systems in Turkey: a review (pp 115-119) |
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Turkey’s natural river systems have been anthropogenically altered in the past century. Native fish communities of river systems have come under increasing
pressure from water engineering projects, pollution, overfishing and the movements of alien fish species. Introduction of alien fishes is one of the main threats
to the survival and genetic integrity of native fishes around the world. In Turkey, alien freshwater fish are continuing to increase in number of species, abundance,
and distribution. The present paper reviews fish stocking studies in Turkey’s reservoirs.
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