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Abstract
Theoretical models imply that seed predation significantly influences population structure which translates to the entire community. As such, empirical studies carried out in a diversity of niches suggest that post-dispersal seed predation accounts for greater seed loss. Given this, a study carried out with an objective of, first, to determine the impact of seed predation on seed environment (covered and open), and second, to determine the same on the seed sizes were carried out.
The experimental design was such that four treatments were designed with each having five traits, which held clusters of 20 seeds each. Noteworthy, the experiment was carried out on an ‘observatory hill’ where an entire cluster of seeds (either sunflower or lentils) was replaced on observing a decrease in quantity. The records of the seed population were taken daily within a fixed period for five consecutive days. The data was then analyzed using Chi-square.
The analysis revealed that there was no significant difference on both occasions at 95% CI. As such, there was a negligible impact of seed predation on such scenarios. To this end, to achieve accurate results, future designs should try to eliminate the effects of artificial factors e.g. transfer of chemicals to seeds where bare hands (without gloves) are used when introducing the seeds to the site.
Introduction
Theoretical models suggest that seed predation significantly functions to structure plant population which translates to the larger community. To this end, empirical studies carried out in a diversity of niches contend that post-dispersal seed predation presents a potential cause of extensive seed loss (Howe & Miriti, 2004). Nevertheless, many other factors may hinder the seedling establishment, and as such their effects can dwarf seed predation.
For instance, with an unfavorable microsite, the effect of seed predation on plant recruitment is decimated. Moreover, excessive protection typified by most perennial plants which provide safe sites (seed banks) for seeds limits seedling establishment. To date, even with well-documented literature on the degree of predator influence on seed abundance, the link between their dynamics remains unclear. This is owed to the fact that there are limited studies done on the same even on areas where the situation seems alarming.
It is tricky to give a general statement on predators’ degree of influence on plant recruitment. This is so because of the striking and varied distinct traits displayed by seeds that don the earth. As such, the susceptibility of seeds to predators varies, for example, with size, strength, and the presence of elaiosomes. Moreover, an ecosystem may host a diverse number of predators that have different preferences thus altering plant population in a complex manner.
In synopsis, a combination of these factors results in a complex community structure. However, seed predators should not be condemned since they too are beneficial. For instance, predation could lead to seed pollination of a mature seed (post-dispersal) that presents a potential new adult in the community. Nevertheless, predation is harmful when a seed in question is premature (pre-dispersal predation) since at this stage it cannot grow even with a favorable microsite. As such, we are tempted to scrutinize the role of seed dispersal in seed recruitment.
Fundamentally, seed dispersal represents “one of the most ecologically significant plant-animal mutualisms and it is central for understanding plant population and community structure” (Bronstein, Alarcón & Gerber, 2006). Depending on the kind of interaction, the net outcome could eventuate in mutualism or antagonism. Nevertheless, the location of the seed after dispersal is what determines whether a seed would grow or not. Therefore, it follows that there are indeed sites that could support seed recruitment in a community while others would not. The microsites that would support seed recruitment (safe sites) provide protection of seeds from predators and at the same time support their growth.
In essence, seeds must be secured from discovery by predators to enhance their chances of growth. Some of the protective sites include a probable crack present in the soil that a seed might land in, a canopy of leafy plants, and a covering of trash. Nonetheless, this should enhance the ecological factors that boost seed recruitment in a community. Given seed protection, the act of dispersal may on the other handguard seeds from predators.
Seeds that find themselves by chance within a parent’s proximity are more susceptible to predator attack than those that are far away (Zwolak & Crone, 2012). In essence, these seeds would easily be spotted by predators that target the parent. Moreover, even if the seeds are dispersed far away from the parents, they might present a potential target for attack by predators when they happen in clusters. For instance, this is common in legumes that have seeds embedded within pods. If by chance the pods fail to burst in the course of dispersion then the seeds will be in clusters. Consequently, they would easily be spotted by a predator (Ordoñez, Molowny-Horas & Retana, 2006).
Noteworthy, some seeds are responsible for protecting themselves from predator attacks thanks to their peculiar nature. In essence, seed discovery and consumption are two separate things. The fact that a seed has been spotted by a predator does not mean that it is in jeopardy. Different kinds of seeds offer unique and varied modes of predator repellant traits. For instance, some seeds have a bad taste while others are toxic to predators.
To this end, we may refer to the infamous castor bean. Commonly found in our niche is the seed of ‘antelope brush’ (Purshia tridentata). This seed is extremely bitter thus deterring predator attack. Moreover, small-sized seeds might be a deterrent to predator attacks. For instance, to a vole, it is uneconomical to explore minute seeds that do not exceed a millimeter in length. This is despite their occurrence in clusters.
A vole considers it a waste of time. In a nutshell, “the size, palatability, and distribution of seed found on the soil surface in a community may greatly influence which seeds are taken by predators” (Andersen, 1989). This will in turn determine which species germinated and hence assume a large role in the ecosystem. As such, the objective of this report is divided into two: first, is to determine that there is no significant difference in seed predation between plants planted within protected (covered) and unprotected (open) environs hence our first null hypothesis (H01); second, is to determine that there is no significant difference in seed predation with regards to seed sizes hence our second null hypothesis (H02).
The experimental design was set up on an ‘observatory hill’ where the daily seed populations were monitored for analysis.
Methods
In this experiment, seeds of lentils and sunflower were placed on ‘observatory hill,’ but on known locations. The seeds were placed in clusters but along transects in a community. Noteworthy, depending on the expected questions the seeds were either placed in direct contact with the ground, or on aluminum dishes. To this end, the essence was to prevent them from being blown away by the wind. This would, however, bring in an artificial factor that could alter the final results.
The experimental design decided was such that four treatments were set composing of five traits each, and holding clusters of 20 seeds per trait. In a nutshell, 2000 seeds were used. Two treatments were meant for sunflower seeds, one for lentils, and a final one that contained both at equal ratios. The seeds populations were to be checked and recorded for each of the five consecutive days, but periodically. Fundamentally, on noticing reduced population per location in the previous census, instead of replacing the lost ones, the entire population of seeds was to be replaced by new ones. Of note, with five members per group, each student was given a chance to count and record the observation in the course of the experiment. The data obtained were then analyzed using Chi-square to test the framed hypotheses.
Results
Table 1. Chi-square analysis on the impact of seed predation on the nature of seed environment (covered or uncovered)
The test value (0.17153) at 1 degree of freedom does not exceed the critical value 3.84. Therefore, there is no significant difference between treatments because the p-value is not less than or equal to 0.05. For more information see appendix 1.
Table 2. Chi-square analysis on the impact of seed predation on the grain size.
The test value (0.00733) at 1 degree of freedom does not exceed the critical value of 3.84. Therefore, there is no significant difference between treatments because the p-value is not less than or equal to 0.05. For more information see appendix 2.
Discussion
The objective of this experiment was partly to determine whether there exists seed predation among seeds placed in different environs (protected or unprotected), and partly to determine whether the same is true with seed sizes. The species under observation were sunflower and lentil seeds. Using Chi-square analysis (tables 1 and 2) the results of the experiment were presented.
With regards to the impact of seed predation on the nature of the seed environment, the analysis revealed that there was no significant difference between covered and uncovered seed environs at a 95% confidence interval. Basically, at 1 degree of freedom, the test value (0.17153) was below the critical value (3.84). As such, we conclude that there is no seed predation between distinct seed environs (in this case covered and open environs) in sunflower seeds. In an ideal ecosystem, the contrary would have happened since we expect seeds that are in an open environment to be more vulnerable to predation. This would happen because they are more likely to be seen than the covered ones.
However, there might have been so many other factors that might have contributed to the recorded observations. For example, there is the likelihood that sunflower seed predators were limited hence the impact was not substantial. Moreover, the seeds probably deterred predators by either chemical emissions or grain strength. Other factors that might have contributed to this observation might have emanated from the person performing the test. For instance, handling seeds with bare hands devoid of gloves might transfer predator-repellant chemicals to the seeds.
Concerning the impact of seed predation on the grain size, the analysis revealed that there was no significant difference between seed sizes (sunflower and lentils) at a 95% confidence interval. Basically, at 1 degree of freedom, the test value (0.00733) was below the critical value (3.84).
Therefore, we conclude that seed predation among seed sizes (lentils and sunflower seeds) was absent. Basically, on relying on seed sizes alone without keeping other factors constant the ensuing results would not reflect the true picture. Ideally, seed predators have diverse taste preferences which cut across grain sizes. As such, given a variety of grain species with different sizes, it is no surprise that a predator would opt for a smaller grain. In a nutshell, on the ‘observatory hill,’ there is the likelihood that there was a limited population of preferred predators (of lentils and sunflower).
However, in an ideal situation where the two samples (lentils and sunflower seeds) present equal preferences to a consumer (predator) than sunflower seeds (big size) would be the most targeted. Other factors that might have contributed to the observation above could have emanated from the nature of the seed. For example, toxics and bitterness act as predator repellants. Moreover, there could have been an artificial factor that sneaked into the system e.g. chemicals present on the hands where gloves were not used during seed placement.
In the future, to obtain accurate results then the person should be advised to use gloves when placing the seeds to minimize the introduction of an artificial factor. Also, on determining the impact of seed predation on the grain size, the design should dwell on one variety of seeds to eliminate the effect of taste preferences. Finally, the ‘observatory hill’ chosen ought to be diversified to be a representative of a natural ecosystem.
In a conclusion, the experimental design met its objective which was to partly determine whether there exists seed predation among seeds (sunflower) placed in different environs (covered or open), and partly to determine whether the same is true with seed sizes (sunflower and lentil seeds). As such, it was concluded that in both scenarios there was no significant difference in seed predation.
References
Andersen, A. (1989). How important is seed predation to recruitment in stable populations of long-lived perennials? Oecologia, 81 (1), 310–315.
Bronstein, J., Alarcón, R. & Gerber, M. (2006). The evolution of plant-insect mutualisms. New Phytol 172 (1), 412–428.
Howe, H. & Miriti, N. (2004) When seed dispersal matters. Journal of Bioscience, 54 (1), 651–660.
Ordoñez, L., Molowny-Horas, R. & Retana, J. (2006). A model of the recruitment of Pinus nigra from unburned edges after large wildfires. Ecol Model, 197 (1), 405–417.
Zwolak, R & Crone, E. (2012) Quantifying the outcome of plant-granivore interactions. Oikos Journals, 121 (1), 20–27.
Appendix
Appendix 1
Table of sunflower population grown in open/covered environment
Appendix 2
Table of sunflower and lentil seeds population sharing the same area on one part, and lentil seed population placed separately on the other part.
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