The relationships existent between biotic and abiotic interactions with regard to plant population dynamics is a fundamental ecological question. Ultimately, the impacts of environmental factors on the dynamics of population present as differences in species distributions, population sizes and density. All factors that influence population dynamics basically act through their effects on the survival, individual growth and fertility rates on any given species. The pattern of species distribution and/or abundance is a cumulative result of the variabilities in population growth rates in different environments.
This implies that studies correlating population densities and environmental factors are in essence unraveling the mechanisms that govern species abundance and distribution. Additionally, knowledge on such mechanisms plays an important role in predicting population growth and species variability in changing environment composition. This prediction buttresses the knowledge that plant population dynamics are directly influenced by climatic changes, eutrophication and succession hence laying the framework for the identification and protection of rare, threatened and endangered species (Dahlgren & Ehrlen 2009).
Abiotic and biotic factors define species niche boundaries. Abiotic factors include light availability, nutrient concentrations and history of catastrophic events. These factors profound effects on population growth rates. Biotic interactions such as herbivory intensity and population growth are can negatively impact on species distribution and abundance such as in forest herb, Actaea spicata (Dahlgren & Ehrlen 2009). The negative impact is due to competition for crucial resources for plant growth and increase in population size.
History is another important aspect in studying plant population dynamics. Historical events can be used to explain the geographical distribution of plant species, population structure and community densities. At the individual species level, historical events experienced in the past but which possess an influence on the future performance are most likely restricted in perennial species with a complex system of carryover mechanisms. Such mechanisms subsequently influence the species growth rates, stable stage distribution, reproductive values and elasticities (Ehrlein 2000).
Current phenotypes of perennial species and specific response to environmental changes are often a reflection of an individual’s history. Environmental conditions such as herbivory can be carried over to ensure species survival and growth. Maron & Crone (2006) studied the impact of herbivory on plant growth, abundance and distribution. Generally, plants are the template upon which food webs are built and communities and ecosystems assembled. For this reason, the impact of herbivory on population growth and dynamics is of supreme importance in ecological studies.
On individual levels, herbivore feeding habits have a strong and negative impact on the growth, reproduction and survival of plants. On a broader scale, herbivore driven decreases in plant performance rates greatly impacts on the long term patterns of abundance, dynamics and distribution. Long term studies of plant communities have demonstrated that consumers influence plant community composition. These effects occur due to direct and/or indirect consumptive patterns of herbivores. Seed production is one of the most critical stages in plant life history.
Adult replacement, increase in population size and the seed dispersal cannot be achieved without efficient seed production mechanisms. Seed predation by insects and animals has profound effects on seed mortality which subsequently influences plant evolution, abundance and distribution. (Zhang et al 1997; Dahlgren & Ehrlen 2009). Usually seed predation can either be categorized into two broad classes of pre-dispersal predation and post-dispersal predation or in other cases pre-seed fall predation and post-seed fall predation. Many species of insects and animals are involved in seed predation.
The most common insects include; Lepidoptera, Diptera, Hymenoptera, Coleoptera and Thysanoptera. Both larval as well as adult insects can be seed predators. A classic example of this case is the carabid beetle, Harpalus rufipes. Other seed predators include peccaries, birds, squirrels, deer and mice. Pre-dispersal predation causes mortality of 80% of all seeds produced in forest and grassland habitats. Post-dispersal predation determines plant distribution patterns, seed survival and plant species composition (Zhang et al 1997).
Plant genetics and other life history traits also directly affect growth and dynamics. r-selected traits and vegetative reproduction mechanisms confer a plant with characteristics such as shorter generation times coupled to high reproduction rates and individual growth have been identified as key traits associated with plant invasiveness. The study of these factors is important because of the large scale nature of economic and environmental impacts of plant invasions. These invasive species negatively affect diversity.
Invading species have the capacity to completely displace native plant species hence leading to the alteration of ecosystem level properties like hydrologic cycles, fire regime, nutrient cycling, sediment deposition and erosion (Engelen & Santos 2009). Additionally, habitat fragmentation which is a direct result of genetic signatures influences the viability of plant populations. Genetics affects fitness components and the conservational status of any given plant species (Pico 2004).
There are several biotic, abiotic and genetic determinants of plant growth, population and dynamics. The interrelationships between all these factors ensure the viability and survival of plant species in different environment and subsequently the global abundance, distribution and population size of different plants. While research has been extremely fruitful in unraveling some of these interrelations, there remains a paucity of research on reliable population prediction mechanisms in the current context of global warming and climate change.
Dahlgren, J. P. , & Ehrlen, J. (July 2009). Linking Environmental Variation to Population Dynamics of a Forest Herb. Journal of Ecology. 97(4): 666-674 Ehrlen, J. (June 2000). The Dynamics of Plant Populations: Does the History of Individuals Matter? Journal of Ecology. 88(3):371-549 Engelen, A. , & Santos, R. (July 2009). Which Demographic Traits Determine Population Growth in the Invasive Brown Seaweed Sargassum muticum? Journal of Ecology. 97(4); 675-684 Maron, J. L. , & Crone, E. (October 2006).
Herbivory: Effects on Plant Abundance, Distribution and Population Growth. Proc Biol Sci. 273(1601): 2575-2584 Pico, F. X. (2004). Genetics Does Matter For Population Dynamics: Demographic Implications of Inbreeding Depression in Plants. Recent Res. Devel. Environ. Biol. 1: 1-14 Zhang, J. , Drummond, A. F. , Liebman, M. , Hartke, A. (1997). Insect Predation of Seeds and Plant Population Dynamics. Maine Agricultural and Forest Experiment Station. University of Maine. Technical Bulletin 163: 1-23