Download A Comparison of Pollinator Landings on Lantana camara with Three

A Comparison of Pollinator Landings on Lantana camara with Three
Other Plant Species in Bloom at Forest Trails, Karnataka, India.
Melissa Forester
June 2010
Abstract
Pollinators have preferences in their selection of plant species on which to feed. Lantana
camara is an invasive plant that is decreasing plant biodiversity across India. How will this
affect pollinators who feed on the plants that are giving way to Lantana camara? This study
seeks to learn about the relationship between plants and their pollinators. This study
counts the landings of butterflies, bees, and other pollinators on Lantana camara and three
other plant species in bloom at Forest Trails, Karnataka: milkweed (Calitropis giganteum),
touch-me-not (Mimosa pudica,) and periwinkle (Catharanthus roseus). The number of
available inflorescences is determined for each plant and the number of landings recorded.
The data shows that while Lantana camara had a greater percentage of landing sites, it
received a smaller percentage of the landings than did Calitropis giganteum or Mimosa
pudica. More interesting, the study showed that most pollinators were host species specific.
Introduction
Butterflies do not feed indiscriminately from any flowers that they may find; they have
preferences for nectar with regard to its chemical composition, corolla tube length and
height of flower (Gadgil in Kunte 2000). When butterflies (and other pollinators) feed from
a flower they help in the pollination of that plant species (Gadgil in Kunte, 2000). Lantana
camara is one of the ten worst invasive weeds in the world and is decreasing the
biodiversity of plant species in one of the planet’s biodiversity hot spots - the Western
Ghats (Dr. Arvind, pers. com 2010).
This study was conducted at Forest Trails, which borders Bannerghatta National Park in
Karnataka, India, where plant diversity is giving way to encroaching Lantana camara. What
will happen to other organisms that live in these forests as the plant species composition
changes? To understand how pollinator species may be affected by changing plant species
composition, there first must be knowledge about local plant-pollinator relationships. This
study is an attempt to get to know the local plant-pollinator relationships.
This study compares pollinator landings on Lantana camara with three other local plant
species: milkweed (Calitropis giganteum), touch-me-not (Mimosa pudica,) and periwinkle
(Catharanthus roseus). It is expected that different species of pollinators will not
indiscriminately land on different plant species, but will select one species more often than
others. Inspired by work the Ashoka Trust for Research for Ecology and the Environment
(ATREE) has done involving high school students with data collection about local bird
populations, this study was created with the intention of conducting a research project that
could be replicated with students in a 9th grade biology class in the US, involving them in
meaningful data collection that develops a body of local ecological knowledge.
Methods
An individual blooming plant of Lantana camara, milkweed (Calitropis giganteum), touchme-not (Mimosa pudica,) and periwinkle (Catharanthus roseus) was selected for
observation, based on their proximity to a Lantana camara plant of similar height. This
allowed each of the three plant species to be observed simultaneously with a Lantana
camara plant and minimized other variables that could affect number of landings recorded,
(such as time of observation). The observer sat at an equal distance from each plant. Three
periods of observations were conducted of one hour each. Pollinator landings on L. camara
and M. pudica were recorded for one hour at a location with GPS coordinates N 12’ 43.082’
E 077’ 33.625’. Pollinator landings on L. camara and C. roseus were recorded at the same
location for one hour. The third observation recorded pollinator landings on L. camara and
C. giganteum at a location with GPS coordinates N 12’ 43.082’ E 077’ 33.483’. Thus in total
the Lantana plant was observed thrice (one hour each) while each of the others were only
observed once (one hour).
Each inflorescence in view of observer was counted as an available landing site. The total
number of landing sites per plant was recorded. The number of landings that occurred on
each plant was recorded. A landing was counted if either a butterfly stopped on an
inflorescence or another pollinator touched it. For examples, bees were never observed to
land on a plant but would visit a flower by touching it with their proboscis. For each plant,
the number of landings is divided by the number of available landing sites. The quotient
gives us the number of pollinator landings per available site.
Results/Analysis
As shown in Appendix 1, 110 pollinator landings were recorded. Each plant observed
received a visit from a pollinator. Calitropis giganteum had 16 landing sites, Mimosa pudica
7, Catharanthus roseus 5, and L. camara 72 landing sites. The total number of landing sites
for the study was 100 (that number is based on the total number of landing sites in view of
observer and not intentional).
Figure 1 shows that six different species of pollinators were recorded landing on the plants
being observed. The chart shows that each pollinator visited only one of the four plants. A
tiny bee visited Catharanthus roseus. A small bee visited Mimosa Pudica. A large bee
visited Calitropus giganteum. Only Lantana camara received landings by more than one
species of pollinator: Blue Tiger (Tirumala limniace) and Common Rose (Pachliopta
aristolochiae) butterflies and a third pollinator which is referred to as “Hummingbird Bee”
in this study.
Figure 1
Number of
Landings
66
64
62
60
58
56
54
52
50
48
46
44
42
40
38
36
34
32
30
28
26
24
22
20
18
16
14
12
10
8
6
4
2
0
Available
Landing Sites
Tirumala limniace (3)
Pachliopta aristolochiae (2)
Hummingbird Bee (52)
Large Bee (34)
Small Bee (17)
Tiny Bee (2)
Catharanthus roseus
Calitropis
giganteum
Mimosa pudica
5
7
Lantana camara
57
Key
Blue Tiger Butterfly (Tirumala limniace)
Common Rose Butterfly (Pachliopta aristolochiae)
Hummingbird Bee
Large Bee
Small Bee
Tiny Bee
Figure 1 shows a direct relationship between the number of available inflorescences and the number of
pollinator landings.
72
Table 1 is a comparison of the number of pollinator landings per plant between the four
plant species in observation. Calitropis giganteum received 2.13 landings for every landing
site. Mimosa pudica received 2.43 pollinator landings for every available site. Both plants
were favored by pollinator visits over Lantana camara, which received less than one visit
for each of its landing sites at .79 visits per site. Catharanthus roseus received the least
visits per site at only .4 visits for each available landing site.
Table 1
Proportion of
Plant Species
Landings Received
Per Available Site
2.13
Calitropis giganteum
2.43
Mimosa pudica
0.4
Catharanthus roseus
0.79
Lantana camara
Table 1: A comparison between four plant species, in
bloom at Forest Trails, Karnataka, of the number of
pollinator visits received per inflorescence.
Table 2 shows that while Lantana camara had 57% of the available landing sites, it only
received 52% of the landings in the study. In comparison Calitropis giganteum had only
16% of the available landing sites and received 31% of the landings. Similarly Mimosa
pudica had 7% of the available sites and received 15% of the landings. The percentage of
landings on both Calitropis giganteum and Mimosa pudica were about double the
percentage of available sites. Both Catharanthus roseus and Lantana camara had landing
percentages that were less than the percentage of available sites. The data from this study
suggest that pollinators are showing some preferential landing on Calitropis giganteum and
Mimosa pudica compared to Catharanthus roseus and Lantana camara.
Table 2
Available
Landings
Plant Species
Landing Sites
Received
16%
31%
Calitropis giganteum
7%
15%
Mimosa pudica
5%
2%
Catharanthus roseus
57%
52%
Lantana camara
Table 2: A comparison between four plant species in bloom at Forest
Trails, Karnataka, of the percentage of the study's available landing
sites and the percentage of pollinator landings observed.
Conclusion
There is difficulty in quantifying pollinator preferences for different plant species. In this
study the quantification of landing sites was problematic. A “landing site” was defined as
an inflorescence in view of the observer. Lantana camara, Calitropis giganteum, and
Mimosa pudica each have inflorescence of multiple flowers while the inflorescence of
Catharanthus roseus consists of a single flower. Pollinators may visit any inflorescence
multiple times because there are multiple flowers. It makes sense for future studies to
count landings per individual flower rather than by inflorescence. This will be more time
consuming and require a lengthier study but should offer more meaningful data. It should
also be taken into consideration that a pollinator may need to make more frequent landings
to small flowers (such as Lantana camera) than to larger flowers (such as Calitropis
giganteum) in order to get the same amount of food. Length of time for landings could be
included as a measurement in future studies.
It was interesting to discover along the way a correlation between the size of the bee and
the size of the flower it visited. In this study, a large bee visited the largest inflorescence
being observed, Calitropis giganteum, and a tiny bee visited Catharanthus roseus. Perhaps
this could be the subject a future study in a high school biology class. A study similar to this
one would be useful in a high school biology classroom because it offered an opportunity to
learn about pollinator-plant relationships and the scientific method through the process.
Students could collect data about which plants pollinators land on in their local
communities in order to develop understanding of local ecological relationships.
Works Cited
Arvind N.A. (Personal Communication) 2010, ATREE, Bangalore.
Kunte, Krushnamegh. India a Lifescape: Butterflies of Peninsular India. University
2000.
Press,