Our modelling study suggests that the relative dispersal distances of seeds and natural enemies are crucial to determining establishment rates and spatial patterns of seedlings. Clumped seed deposition increased the probability of seedling establishment under both insect seed predation and pathogen attack as it led to local satiation of insect seed predators and made it harder for pathogen distributions to track seeds.Ħ. Under pathogen attack, Janzen–Connell patterns predominated except when seedling survival was virtually zero or one everywhere, or in the case where pathogen dispersal distances exceeded seed dispersal distances, producing ‘Hubbell’ patterns in which seed deposition and seedling establishment decrease with distance, though survivorship increases.ĥ. Total seedling establishment was lowest when insects and seeds dispersed similar distances.Ĥ. When insects dispersed longer distances than seeds, higher seed densities near the tree satiated insects, resulting in ‘McCanny’ patterns in which seed deposition, survivorship and seedling establishment all decrease with distance from the parent tree. Under insect seed predation, seeds escaped predation by dispersing longer distances than insects, resulting in ‘Janzen–Connell’ patterns in which seedling recruitment peaks at intermediate distances. We varied dispersal distance, degree of clumping, type of enemy, enemy dispersal distance and fecundity among simulations.ģ. We based our models for seed mortality on published data reflecting differing life histories of insect seed predators and soil-borne pathogens. We simulated clumped seed dispersal by combining a two-dimensional Student’s T dispersal kernel for expected seed rain with a negative binomial distribution for seed deposition. We used spatially explicit simulation models to examine how different patterns of seed dispersal and natural enemy attack structure seedling spatial patterns. Clumped seed deposition is common, especially for vertebrate-dispersed seeds, and has the potential to significantly affect interactions with density-responsive enemies, yet has received relatively little attention.Ģ. Seed dispersal and natural enemies both influence spatial patterns of seedlings, which in turn influence future abiotic and biotic interactions, with consequences for plant populations, distributions and diversity. Various factors like speciation,extinction, continental drift, glaciation, variations of sea levels, river capture, and available resources are useful in understanding species distribution.1. The distribution pattern can change seasonally, in response to the availability of resources and also depending upon the scale at which they are viewed. The distribution of species depends upon various biotic and abiotic factors. The pattern of distribution is not permanent for each species. Example - penguins often exhibit uniform spacing by aggressively defending their territory among their neighbours.Ģ) Random Species Distribution: this is the least common form of distribution in nature and occurs when the members of a given species are found in environments in which the position of each individual is independent of the other individual.Įxample - when dandelion seeds are dispersed by wind, a random distribution occurs as the seedlings land in random places determined by uncontrollable factors.ģ)Clumped Species Distribution: this the most common type of dispersion wherein the distance between neighbouring individuals is minimised.Įxample - the bald eagles nest of eaglets exhibits a clumped distribution because all the offsprings are in a small subset of a survey area before they learn to fly. Uniform distributions are found in populations in which the distance between neighbouring individuals is maximised. There are three basic types of species distribution within an area:ġ) Uniform Species Distribution: in this form the species are evenly spaced.
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