GREGARIOUS RELATIONSHIPS: CHARACTERISTICS, ADVANTAGES AND EXAMPLES - BIOLOGY - 2025

The gregarious relations, also known as gregarious associations or aggregations consist of the spatial union of diverse individuals belonging to the same species, which may be related or not.

This ensemble carries out activities of daily living together, and the relationship confers some kind of benefit to the participants of the aggregation. They are generally related to the search for food, with the protection of the group against long movements (migrations, for example) or with reproduction.

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The duration of the aggregation varies widely depending on the species in question. It can be short-lived or it can be long-lasting. Similarly, the complexity of the association varies.

In the ecological literature there are different terms to name the aggregations depending on the animal group. They can be herds, flocks, schools, packs, among others.

characteristics

The term gregarious comes from the Latin term gregarĭus, which means "tendency to live in herds." In nature, gregarious associations consist of groups of living organisms that carry out different activities in a common physical space, obtaining some benefit from it.

The organisms involved in the relationship belong to the same species and may or may not belong to the same family.

Furthermore, in gregarious relationships we can find a homogeneous distribution of tasks (all organisms contribute in the same way) or they can be hierarchically distributed.

Gregarious associations occur in different animal lineages and their characteristics are quite heterogeneous, since they depend directly on the animal lineage in question.

Quantification of the herd pattern

The three types of spatial distribution

In addition to the herd or grouped pattern, ecologists who study populations establish two basic types of distribution of populations in space and time: uniform and random.

In the uniform distribution the organisms keep the same distance from their partners. It is common in animals that defend their territory and must protect resources that are scarce.

Random distribution is rare in nature, and refers to organisms that do not form social groups with their peers. This distribution requires a partially homogeneous distribution of resources. Although it is not observed in any group of vertebrates, it is possible to see it in certain plants of the tropical forests.

If we are studying a population and we want to verify how the population is distributed, we can use the Morisita index.

Morisita index

This is a mathematical tool that allows us to distinguish between the three spatial distribution patterns. This measure is characterized by not being sensitive to population density when you want to compare between two or more populations that vary significantly in this parameter.

If said aggregation index yields values ​​of one we can conclude that the distribution of our study population is random, if it is less than one the distribution is uniform and if the index is greater than one the population will have a gregarious distribution.

To verify if the test has statistical validity, it is necessary to apply the chi square analysis.

Advantages of a gregarious aggregation

Ease of finding food

Living with other individuals in an intimate relationship should have a number of benefits for the members. The most obvious advantage of a gregarious relationship is easier to find food, since there are several individuals looking for the resource.

Predator avoidance and confusion

Animals that live in large groups can help each other evade predators, as large numbers of prey often create confusion for organisms seeking to consume them.

Increased hunting success

From the point of view of predators, if they hunt together, they will have a greater chance of success. Many herds of carnivores can cooperate to hunt and share the prey.

Increase breeding success

The benefits are also related to reproduction. Some animals present division of tasks and contribution in the care of the young - very demanding activity, in terms of time and energy.

However, sometimes the aggregation of animals (and also plants) can occur as a consequence of the localized distribution of resources.

That is, if food is found only in a restricted portion of the ecosystem, the inhabitants tend to live close to this resource (or any other). In the previous case, there are no social reasons that explain the grouping of the organisms.

Examples

Bee colonies

One of the most complex and dependent gregarious associations that we find in nature are hymenopteran insects. Bees, for example, form colonies where each individual has a specific role and the general objective is to promote the reproduction of the queen.

Under an orthodox Darwinian analysis it would seem illogical - at first glance - for one individual to prefer to contribute to the reproduction of another, at the expense of their own reproductive success. According to research, this altruistic behavior is biased by the type of sex determination that these insects present.

In most hymenopteran insects, sex determination is haplodiploid. The details of the matter are beyond the scope of this article. However, one of the consequences is that the sisters are more related (genetically speaking) to each other than to their own children.

Following this genetic logic, it is "worth it" to invest time and energy in the reproduction of more sister than in generating an own offspring.

Fishes

Many species of fish swim in aggregations. This pattern of behavior has fascinated evolutionary biologists for many years. In fish grouping, natural selection has produced behaviors that ensure group uniformity, call it coherence and cohesion.

As the group progresses, some of its members may be consumed. However, this does not mean that the group will dissolve.

Aggregation makes it easier to evade predators and swimming together helps the confusion effect mentioned above.

Packs of lions

Most lions live in packs, being one of the most cooperative felines. These are made up of more than 10 or 20 lions. These are territorial, where the males defend their space and prevent another alien individual from entering the area.

The female, for her part, is in charge of looking for food to feed her young. Males offer protection.

References

1. Cech, JJ, & Moyle, PB (2000). Fishes: an introduction to ichthyology. Prentice-Hall.
2. Hickman, CP, Roberts, LS, Larson, A., Ober, WC, & Garrison, C. (2001). Integrated Principles of Zoology. New York: McGraw-Hill.
3. Kapoor, BG, & Khanna, B. (2004). Ichthyology handbook. Springer Science & Business Media.
4. Koenig, WD, & Dickinson, JL (Eds.). (2004). Ecology and evolution of cooperative breeding in birds. Cambridge University Press.
5. Parrish, JK, & Hamner, WM (Eds.). (1997). Animal groups in three dimensions: how species aggregate. Cambridge University Press.
6. Pianka, ER (2011). Evolutionary ecology. E-book.