Species Composition of Ants (Hymenoptera: Formicidae) and Thermal Tolerance along Environmental Gradient in the Bale Mountains National Park (BMNP), Ethiopia
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Date
2017-01
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Addis Ababa University
Abstract
This study was conducted to investigate the species composition of ants (Hymenoptera:
Formicidea) and thermal tolerance of Camponotus negus and Camponotus acvapimensis
in the Bale Mountains National Park (BMNP), Ethiopia. Ants were collected from
different altitudes and habitats using manual search, baits and pitfall traps from
December 14, 2013 to October 08, 2015. Heat and cold tolerance of ant colonies (C.
negus) from different altitudes of the BMNP (Gaysay and Sanetti) and from Dilla (C.
acvapimensis) was determined. The time taken (minutes) by ant colonies to lose mobility
at a stressfully high temperature (knock-down resistance) of colonies were measured
from each site as an index of heat tolerance. For heat tolerance experiment 10 to 12
individuals from each colony (for a minimum of 24 individuals per colony) were placed
into two Petri dishes in identical water baths (Stuart digital water bath, RE300DB, Keison
International Ltd, UK). Initially the temperature in both baths was set and maintained at
45 °C for 90 minutes. After 90 minutes, the temperature was raised by 5 °C, and
continued to rise by 5 °C every 30 minutes thereafter until all ants had succumbed to heat
stress. Time was recorded starting from the time the first ant completely lost mobility till
the last ant stopped moving. The time required for an individual to recover from exposure
to extremely low temperatures (chill-coma recovery) was used to assess cold tolerance of
ants. For cold tolerance experiments, 24 to 27 ants from each colony were placed in a
Petri dish covered in ice for 20 minutes. Then the time for each individual to recover
from chill-comma was recorded. From a total of 162 sample collections made, 16 species
under 8 genera and 4 subfamilies namely; Dorylinae, Formicinae, Myrmicinae and
Ponerinae were identified. Subfamily Myrmicinae was the most diverse with nine species
iv | P a g e
(56.25%) and the genus Tetramorium was the most speciose containing five species. C.
negus was the most abundant species of 54.12% of the samples collected. The highest ant
species diversity was observed in the altitude range of 2000– 2500 m followed by 3000–
3500 m and the lowest was in the altitude range of 2500– 3000 m and 3500–4000 m.
Thus there was no clear pattern of species diversity with elevation. The highest ant
species diversity was recorded from the rainforest. C. negus from Sanetti (3970 m) had
high heat tolerance (143.52 ± 1.80 minutes) than from Gaysay (3040 m) (98.30 ± 1.82)
minutes, but cold tolerance did not differ between the two sites. Colonies from Sanetti on
average tolerated heat for additional 45 minutes compared to Gaysay. C. acvapimensis
had similar heat tolerance as C. negus from Sanetti but it had very low cold tolerance
which took 549.79 ± 18.77 seconds to recover from chill-comma compared to C. negus
from both Gaysay and Sanetti which were 113.94 ± 19.40 and 84.04 ± 18.77 seconds
respectively. C. acvapimensis needed nearly 5 times more time to recover from chillcoma
compared to colonies of C. negus from Gaysay and 6 times than C. negus from
Sanetti. Hence C. negus from Sanetti had higher heat and cold tolerance and may have
higher potential to survive in the changing climate of BMNP. In conclusion, there was no
clear pattern of species diversity with elevation and the diversity was the highest in the
rainforest. C. negus from Sanetti had higher heat and cold tolerance and may has higher
chance of survival in the changing climate.
Key words: ants, diversity, climate change, thermal tolerance, Camponotus negus,
Camponotus acvapimensis, Bale Mountains National Park
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Keywords
Ants, Diversity, Climate Change, Thermal Tolerance, Camponotus Negus, Camponotus Acvapimensis, Bale Mountains National Park