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Biological dispersal

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**1. Types of Dispersal**

– **Passive Dispersal (Density-Independent Dispersal):**
– Invertebrates use water currents for gamete dispersal.
– Plants utilize wind, water, or animals for seed transportation.
– Larval phase allows movement for some invertebrates and fish.
– Kinetic energy in the environment aids in dispersal.

– **Active Dispersal (Density-Dependent Dispersal):**
– Animals move independently for location change.
– Dispersion influenced by population density and resources.
– Walking animals face barriers limiting dispersal.
– Flying, swimming, or walking enable long-distance movement.
– Helps relieve resource pressure and competition in ecosystems.

**2. Costs and Benefits of Dispersal**

– Fitness benefits outweigh costs in dispersal.
– Benefits include finding new resources and avoiding inbreeding.
– Costs involve energy, risk, time, and opportunity.
– Dispersal may lead to outbreeding depression.
– Social animals face challenges in finding new groups.

**3. Environmental Constraints and Dispersal Range**

– Species distribution varies across landscapes based on environmental features.
– Dispersal range refers to the species’ ability to move from existing populations.
– Critical for ecosystem stability and habitat patch connectivity.
– Urban areas impact dispersal abilities of organisms.
– Development in urban areas can limit dispersal.

**4. Dispersal Barriers and Mechanisms**

– Dispersal barriers, like habitat fragmentation, can limit species distribution.
– Natural barriers, such as mountain ranges and rivers, can restrict dispersal.
– Animals and plants disperse through various mechanisms like locomotion and seed dispersal.
– Dispersal mechanisms can lead to genetic isolation and allopatric speciation.
– Human activities can expand species dispersal, leading to invasive species.

**5. Quantifying Dispersal and Human-Mediated Dispersal**

– Dispersal is quantified in terms of rate or distance.
– Consequences of dispersal impact populations and species on ecological and evolutionary scales.
– Human-mediated dispersal alters animal movement patterns significantly.
– Human impact can influence dispersal range variations and patterns.
– Various methods like landscape genetics and direct tracking are used to study dispersal.

Biological dispersal refers to both the movement of individuals (animals, plants, fungi, bacteria, etc.) from their birth site to their breeding site ('natal dispersal'), as well as the movement from one breeding site to another ('breeding dispersal'). Dispersal is also used to describe the movement of propagules such as seeds and spores. Technically, dispersal is defined as any movement that has the potential to lead to gene flow. The act of dispersal involves three phases: departure, transfer, settlement and there are different fitness costs and benefits associated with each of these phases. Through simply moving from one habitat patch to another, the dispersal of an individual has consequences not only for individual fitness, but also for population dynamics, population genetics, and species distribution. Understanding dispersal and the consequences both for evolutionary strategies at a species level, and for processes at an ecosystem level, requires understanding on the type of dispersal, the dispersal range of a given species, and the dispersal mechanisms involved. Biological dispersal can be correlated to population density. The range of variations of a species' location determines expansion range.

A dandelion seed caught in a spider web strand. Dandelions disperse seeds via wind currents.
Dispersal of lichen soredia (visualized using ultraviolet light) by a spider

Biological dispersal may be contrasted with geodispersal, which is the mixing of previously isolated populations (or whole biotas) following the erosion of geographic barriers to dispersal or gene flow (Lieberman, 2005; Albert and Reis, 2011).

Dispersal can be distinguished from animal migration (typically round-trip seasonal movement), although within the population genetics literature, the terms 'migration' and 'dispersal' are often used interchangeably.

Furthermore, biological dispersal is impacted and limited by different environmental conditions. This leads to a wide range of consequences on the organisms present in the environment and their ability to adapt their dispersal methods to that environment.

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