Trait distributions of prickly pear cactus – W4D2B

Oct 6, 2015

Trait distributions of prickly pear cactus (Opuntia spp.) in the Pinyon Juniper Habitat of Western Colorado.

Betts, S;  Abeywickrema, M; Jet, L; Garrett, J; & Berdichevsky, K.

Abstract:  After observing a variation in the traits of Opuntia spp. on the Pinyon Juniper mesas above Paonia, CO, the authors questioned whether two distinct species existed in the area.  The authors began to collect data on 6 separate traits of cacti that they encountered. Each of the authors found various correlations that led the group to conclude that there were in fact two different species; a shorter smaller variety with less fruit and a larger variety with a larger concentration of fruit.

Introduction:  The authors observed variation in the traits of prickly pear cactus (Opuntia spp.) on the Pinyon Juniper mesas above Paonia, CO.   We questioned whether there were two or more distinct species or whether there was a continuous range  in traits of a single species. 

Methods:  We determined 6 separate traits to measure in a cactus.  They were (1) length of the longest pad, (2) width of the longest pad, (3) Height of the plant, (4) number of fruit, (5) presence of long spines on the fruit, and (6) level of distinct bumps on the pad.   Each of the authors collected data from 10 different cactus as encountered in different directions of travel.  In total 60 cactus were measured. 

Results: Each of the authors chose a various correlation to examine. We found 5 significant results.

Lily Jet examined the correlation between bumps and spines on the fruit by creating a Chi-square table. Statistical analysis of the data proved a p < 0.05.

The Chi-square statistic is 4.0727. The P value is 0.043581. This result is significant at p < 0.05.


Katie Berdichevsky averaged the length of all the longest pads in each of two categories: cactus pads with bumps, and cactus pads without bumps. Cactus length in the “No Bumps” category averaged at 6.1 inches and cactus in the “Bumps” category averaged at 3.2 inches.

Jack Garrett compared the lengths of the longest pads to the number of fruit located on each of the plants.  The graphed data revealed a concentration of data points with shorter pad lengths and zero fruit. All the data points with high numbers of fruit had longer pad lengths.

Spencer Betts averaged out the correlation between those specimen containing spiny-fruit and those with spineless fruit and the heights of the respective specimen. It was discovered that the average height of those specimen containing spiny-fruit was 5.96153846 inches. The average height of those specimen with spineless fruit was 8.88888889 inches.

Max looked at the correlation between pad length and width.  He found that the two correlated with longer pads being wider.  Sometimes there were exceptions with long, narrow and thick pads. 


Traits all correlated in clusters.  There seems to be two distinct types of Opuntia.  Type 1 tends to have longer pads, wider pads, with lots of spineless fruit and flat pads.

Type 2 has shorter pads and narrower pads, few to no fruit, spiny fruit, bumps on the pads.  We recommended genetic studies to determine species differentiation.

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