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Bee Visits to Calathea
insignis in Primary vs. Edge Forest
Karen Almena, Jeannie Oakray, Sim Huang, Bruce McCandles, Pam Norton
Abstract
We
observed the number of bee visits to the inflorescence of the rattlesnake plant
(Calathea insignis) over the course of a two-day period. Our observations were made at the edge of
the secondary forest and within the primary forest of the Las Cruces Biological
Station near San Vito, Costa Rica. The
primary forest site received approximately twice the number of insect visits
than the edge environment.
Introduction
Description of Calathea insignis (Rattlesnake plant)
The rattlesnake plant is a commonly
encountered large understory herb belonging to the family Marantacae. This species occurs from Mexico to
Ecuador. In Costa Rica it is found from
sea level to 1500m at Monteverde and near San Vito in semi-deciduous and
pre-montane wet forest. Plants in the
San Vito area are usually less than 2.5m tall.
Flowering
usually occurs in the rainy season. The
bright yellow inflorescences consist of a series of bracts. Flower maturation begins at the base of the
inflorescence and proceeds up in an orderly fashion. The next higher bract flowers each day. The flowers are visited solely for their nectar. The rattlesnake plant is self compatible as
well as a cross pollinator.
In the San Vito area on an average only
one-third of the flowers are pollinated.
Of those visited by pollinators fewer than 50% contain pollen. The chief pollinator in the flowers at Las
Cruces was a ground bee, Thygater sp.
Visits by pollinators are more frequent
on sunny days. Plants growing at the
disturbed forest edge receive more visits on the average than plants a few
meters into the forest. Under optimal
conditions a plant can go from a single-leafed seedling to a mature flowering
plant in less than two years. (Kennedy,
H. 1978)
We were interested in studying the effect forest disturbance has upon the diversity and number of pollinating insects to the Rattlesnake plant. We predict disturbed (edge effect) plants in the secondary forest will attract a greater diversity and number of insects than undisturbed plants in the primary forest.
Methods and Materials
The study was conducted at Las Cruces Biological field
station in Costa Rica on July 17 and 18, 2000. Two sites were studied. The first was located in the primary forest
and the second location was in the secondary forest of the field station. An initial survey of the area was taken in
order to locate Rattlesnake plants suitable for study. We were informed that flowering species
would be difficult to find in the primary forest area due to dense vegetation.
We chose two plants based upon their location relative
to the trail. The plant located in the
primary forest was in an undisturbed area.
The plant in the secondary forest was located near edge of the trial, an
area disturbed by human intervention. This trail was about 3 meters in width and extended throughout
the secondary forest.
We
used a sling psychrometer to measure relative humidity and temperature and a
GPS to measure elevation. We also used
binoculars and a hand lens to observe insects that were difficult to see.
Insect censusing techniques on Calathea
insignis (Rattlesnake plant)
To measure the status (presence and diversity) of
insect visits to Rattlesnake plant inflouresence and obtain an index of their
abundance we observed the flowers visually.
Group members observed each individual from a distance of 1 meter. Number and species of insects were recorded
for a period of one hour. Observations
took place from 3:09 to 4:09 p.m. on July 17, 2000 and from 8:37 a.m. to 9:37
a.m. on July 18, 2000.
Data
I.
Observations at primary forest site
Site Description:
Elevation:
3880 feet
above sea level.
Slope: East at about 45 to 60
degrees.
General Description: The plant was on the west side of a 150-foot tall tree with strangler fig roots on it. The tree was about one foot away and was covered with mossy ferns.
Plant Description:
The plant is four feet tall. The yellow laterally flattened, rectangular inflorescence is two feet tall with five flowers on one stalk. Two florets are on the southeast side and three are on the northwest side. There are thirteen healthy leaves on this plant, though four are mottled with fungus type spots. Six leaves have edges that appear chewed. The four mottled leaves are angled 45 degrees toward a canopy opening. Four and one half feet away to the southwest are two clumps of similar plants. The ground cover is leaf litter and is consistent. Roots are exposed on nearby plants and vines. The inflorescence has 12 pairs of folded bracts. The seven top sets of bracts have not florets, the eighth bract on the southeast side has a floret, the ninth bract has no floret, the tenth bract has a floret and there bottom two bracts have no floret. On the northwest side, there are three florets, located on bracts #4, 7, and 8.
Observations at primary forest site on Monday, July
17 from 3:38-4:38:
Weather conditions:
Temperature: 80 degrees
Relative
humidity: 90%
Sky
composition: Overcast
Barometric pressure: 26.10 in (Relative to Carol’s watch)
|
1.
3:45 One unknown small flying insect
landed on a leaf. 2.
3:50 A caddis fly type insect landed on
the northwest leaf. 3.
3:46 A small beetle landed and went into
the fourth bract for one minute, and then into the other side of the same
fourth bract on the southeast side.
It stayed there for one minute and then moved to the fifth bract for
one minute, then the sixth bract and then into the seventh bract where it
went inside above the floret at 4:00 pm.
4.
3:48 A box elder type bug, which was
black with yellow lines, landed on the top of the southwest leaf at
3:48. 5.
3:49 One gnat type insect landed on the
same leaf at 3:49 and remained for two seconds; he went to another leaf and then
came back within seconds. 6.
3:54 An earwig went into the bottom bract
on the southeast side. At 4:07 it
moved to the next bract up. |
7.
4:11
A 1/4-inch long flying hopper
type insect landed on the northwest bottom leaf. 8.
4:12 One white mite appeared on a
leaf. 9.
4:14 An ant appeared on the fifth bract
of the northwest side under the floret and then went into the seventh
bract. 10.
4:12 A white flying mite type insect
landed on the stem of the inflorescence and remained for two seconds. 11.
4:14 A gnat-type fling insect landed on
the northeast leaf, the leaf that is second from the topmost leaf. 12.
4:17 A gnat type insect landed on the
northwest leaf. 13.
4:27 One black fly like insect landed on
the southeast leaf. |
Observations at primary forest site on Tuesday, July 18 from 8:30 to 9:30 were the following:
Weather conditions:
Temperature: 67 degrees
Relative
humidity: 98%
Sky
composition: Overcast
Barometric pressure: 26.29 in (Relative to Carol’s watch)
|
1.
8:37
– beetle, green bee. 2.
8:58
– gnat-like bug on stalk. 3.
9:10
– fly. 4.
9:20
– green bee. 5.
9:26
– fruit fly. |
6.
9:29
– green bee. 7.
9:39
– fruit fly. 8.
9:42
– small black beetle on plant. 9.
9:43
– green bee. 10.
9:46
– green bee. 11.
9:48
– green bee. |
II.
Observations at Secondary
forest site:
Site Description:
Elevation:
3720 feet
above sea level.
Slope: 0 degrees.
General Description: The plant was located 3 feet from the path, and 1 foot from a water drain that ran perpendicular to the path (Figure 1) This plant was located near small tree trunks. There was decaying leaf litter as well as newly formed green vine cover. The forest canopy consisted of 80% coverage (Figure 2). There was a clearing 15 feet to the northeast that resulted from a fallen tree. There was a zero percent grade. There were 4 other influoresences located across the trail within fifteen feet of the influoresence being studied to the east. There were five other ginger influoresences within that location as well. Just located within ten feet of the influoresence being studied, their 7 flower pods to the east as well as two other unidentifiable flowers.
|
Figure 1 |
Figure 2 |
Plant Description:
It was
8 feet tall with 9 leaves that ranged from 4 feet to 8 feet tall (Figure
3). The leaf closest to the trail
exhibited some brown edging. There were
two flowers on the bottom bracts just above each other with the lowest one
being one above the bottom bract (Figure 4).
There were two spent flowers on the other side of the bract on numbers 9
& 11 (from the top).
|
|
|
Observations at Secondary forest
site on Monday, July 17 from 3:36-4:38:
Weather conditions:
Temperature: 75 degrees
Relative
humidity: 86%
Sky
composition: Overcast
Barometric
pressure: 26.15 in (Relative to
Carol’s watch)
The site was very wet due to a recent rainstorm. The Maratha is about 0.5 meter west of the trail. Directly north of the study flower is a drainage ditch. The ground around the plant is flat; a full understory and large trees are nearby. No other flowers were noted in the direct area. The air was calm.
|
1.
3:40
- two gnat-like insects landed on plant. 2.
3:46
– gnat-like insect on floret. 3.
3:47
– fruit fly in floret. 4.
3:51
– earwig in floret. |
5.
3:53
– earwig moved to a different bract. 6.
3:56
– large bee visited general area but did not land on floret. 7.
3:59
– ant on inflorescence caused fruit fly to move to a different location. 8.
4:02
– large bee revisits general area. 9.
4:05
– earwig moves back into floret. |
Observations at Secondary forest
site on Tuesday, July 18 from 8:30-9:30:
Weather conditions:
Temperature: 68 degrees
Relative
humidity: 100%
Sky
composition: Overcast
Barometric pressure: in (Relative to Carol’s watch)
Initial observation:
On first sight, there were small white mites on the bottom bracts nearest the flowers. A small (2 mm) whitish clear millipede was located on the third bract from the bottom. A drosophila fruit fly was crawling on the second bract from the bottom.
|
1.
8:53-black
beetle on the opposite side of the flowering bract, on bract #10. 2.
8:53-black
beetle moved to bract #9. 3.
8:53-black
beetle moved to bract #10. 4.
8:54-black
beetle moved to bract #11 around the spent flower. 5.
8:54-black
beetle moved the outside of the chamber. 6.
8:55-black
beetle moved to the 10th bract. 7.
8:55-black
beetle moved to the 9th bract.
|
10.
8:58-hummingbird
came and left 11.
8:59-gnat
crawled on leaf. 12.
8:59-reddish
and yellow beetle crawled on leaf and left within a minute. 13.
9:01-fly
on the top leaf over the trail to the west. 14.
9:08-bee
with black and yellow stripe visited a nearby flower on a different plant. 15.
9:20-snail
˝ inches long traveled down the stalk next to the flower pod. 16.
9:21-white
mite traveling up the same stalk. 17.
9:22-bee
with black and yellow stripe on abdomen pollinated the flower from another
plant.
|
Classroom Applications
The driving question behind this research was, “Does
human impact affect the number and types of pollinating insects that visit the
rattlesnake plant, as compared to a primary forest?” We feel this question can be applied to the classroom, as all
North American students are experiencing changes in ecosystems and stresses as
a result of human impact. By studying
the difference between areas which have been heavily human impacted to those
that have not, our students can learn about the hidden affects on insect
populations and through awareness, be able to become more involved with their
environment.
Studying the number and type of pollinating insects in
the two different forest types can demonstrate the relative health of the
forest as well as serve as an indicator of changes that are happening as a
result of increased human impact.
Students will be able to apply what they already know about insect
populations and a plants sexual reproduction and through the data collected be
able to create their own conclusion about insect populations and the plants
that they pollinate.
In the classroom, students
will choose two different environment, in which clear differences between human
impact and relatively pristine environments are visible. The students will research the site that
they have chosen and be able to make more informed conclusions about the
changes in the ecosystems and environment as well as being more involved with
their local environments. The students
will perform site sampling of a particular flowering plant species with a
larger amount of plants in their sample.
As time allows, the students will perform this sampling over an extended
period of time to be able to gain a larger database. If time allows, the students may be able to sample the plants for
an extended period of time per sample.
The students will be responsible for presenting their data, both
verbally and in a written report. This
process will allow for the students to become more involved and informed about
their local environment as well as give insight into the scientific process of
inquiry.
Conclusion
The
rattlesnake plant in the primary forest received 10 insect visits versus 9 insect
visits in the edge forest.
Additionally, the primary site received 5 bee visits versus 3 bee visits
at the edge site. The bee responsible
for rattlesnake plant pollination, according to H. Kennedy (Costa Rican
Natural History) is a species of
Euglossine bee. Our data does not support our hypothesis that the
secondary site would receive more insect visits. We did not collect bee specimens and therefore, could not be
certain that the bee visits were made by a Euglossine bee. We suggest that improvements to our study
should include: additional observations
of the rattlesnake plant, a larger number of rattlesnake plants, and collection
of insects for identification.