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Seed dispersal effectiveness increases with body size in New Zealand alpine scree weta Seed dispersal effectiveness increases with body size in New Zealand alpine scree weta

Seed dispersal effectiveness increases with body size in New Zealand alpine scree weta - PowerPoint Presentation

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Seed dispersal effectiveness increases with body size in New Zealand alpine scree weta - PPT Presentation

Deinacrida connectens By Hannah Larsen and Kevin C Burns Background Alpine scree wetas Deinacrida connectens live above the tree line in the South Island of New Zealand The alpine scree weta ID: 792907

seed seeds scree weta seeds seed weta scree size dispersal scat individuals average wetas fruit body captured consumption snowberry

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Slide1

Seed dispersal effectiveness increases with body size in New Zealand alpine scree weta (Deinacrida connectens)By Hannah Larsen and Kevin C. Burns

BackgroundAlpine scree wetas (Deinacrida connectens) live above the tree line in the South Island of New Zealand. The alpine scree weta is sexually dimorphic with females being larger than males. Alpine wetas are known to consume fleshy fruit and disperse the fruit seeds after digestion. The effectiveness of this mutualistic dispersal is under debate. The scree weta’s ability to disperse seeds was tested with the consumption of mountain snowberries (Gaultheria depressa Ericaceae), which produce fleshy fruit (Average seed number ~ 279.67± 12.64 SE). There is much debate over whether the alpine weta is a seed disperser or a seed predator.

Aim

To determine whether Alpine scree weta (

Deinacrida connectens) are seed dispersers (Mutualistic) or seed predators of mountain snowberries (Gaultheria depressa Ericaceae) in New Zealand.HypothesisAlpine scree weta will act as mutualistic seed dispersers (for the mountain snowberry) when large (e.g. adults) and act more as a seed predators when small (e.g. juveniles).

Methods

15 individuals were captured on scree slopes above the tree line in the Nelson lakes National Park on Mt Robert at ~ 1450m above sea level. Upon capture the individuals were

sexed and then measured for

weight and

length.

Individuals

were then

placed in containers and transported back to the laboratory at the base of the mountain.

 

Field O

bservations

Any

scat

that could be identified as coming from

a scree weta in the field

was

gathered and analyzed for the amount of

snowberry seeds

that had

passed through the gut. Captured wetas were subjected to a diet of carrot for 3 days to allow all snowberry seeds to pass through the

gut before experimentation.

 

Consumption

All captured wetas

were given 3 randomly selected snowberries

and the resulting consumption of the

berries was monitored over 48hours. Each

individual weta

was monitored every 4 hours for

the degree of fruit consumption. Every

berry

was categorized

based on amount

consumed by the weta (>

90%,

50

– 90% and

1

– 50

% consumed).

 

Seed P

assage

All captured wetas were given a small block of cheese (~ 3mm in diameter) containing a known number of snowberry seeds. After ingestion, the s

ubsequent

scat was analyzed to determine the amount of viable seeds. To determine the viability of the seeds, 20 were randomly selected and were subjected to a staining procedure with 2,3,5-triphenyl

tetrazolium

chloride (for detailed description of technique read de Vega et al., 2011)

.

 

Movement

Captured individuals were placed in

an arena and their movements were monitored

for 30

seconds. Distances travelled were

measured

with a

flexible

tape measure

and

were

averaged over 3 consecutive nights

between

3 - 4am

.

Slide2

ConclusionWeta show ontogenetic shifts from seed predators at a small size (e.g. young) to mutualistic seed dispersers of the mountain snowberry at the larger adult sizes. There was much variation among the individuals in effectiveness of dispersal results suggesting an increase in effectiveness of dispersal with increased size.

 High correlation of body size to weight (R2=0.95 P< 0.001)Total of 1945 intact seeds were found in the scat of captured wetas. A high variation among individuals was seen.Field scat collection: 40 individual scat found, highly variable in numbers of seeds found in scat, 20 scat held < 50 seeds. A) Consumption: Overall average of 2 snowberries consumed per night (increased with size of individuals R2=0.834 P < 0.001)B) Passage: Average of 31.95% ± 7.73 SE passed through gut intact (increased with size R2=0.609 P < 0.001)C) Seed dispersal vs. body length: Positive correlation R2=0.594 P < 0.001, Average 251.5± 107.8 SE seeds per night.Distance moved: Increased for large wetas (R2=0.598 P < 0.001)  ResultsFig. 1. Relationships between the body size of 15 scree weta and (A) the average number of snowberries consumed per night, (B) proportion of consumed seeds that were passed intact, and (C) extrapolated numbers of seeds dispersed by scree weta per night (nightly fruit consumption rates ¥ average number of seeds per fruit ¥ proportion of seeds passed intact). Reference and recommended readingsde Vega, C., M. Arista, P. L. Ortiz, C. M. Herrera, and S. Talavera. 2011. Endozoochory by beetles: a novel seed dispersal mechanism. Annals of Botany 107: 629-637.King, P., L. Milicich, and K. Burns. 2011. Body size determines rates of seed dispersal by giant king crickets.

Popul Ecol 53: 73-80.

Wyman

, T. E., S. A. Trewick, M. Morgan-Richards, and A. D. L. Noble. 2011. Mutualism or opportunism? Tree fuchsia (Fuchsia excorticata) and tree weta (Hemideina) interactions. Austral Ecology 36: 261-268.Speed Paper Synopsis By Nicholas ScottFig. 2. Relationship between scree weta body size and the average distance (m) weta moved per minute under laboratory conditions.