Mixed-species groups and aggregations: shaping ecological and behavioural patterns and processes

Abstract

Mixed-species groups of birds, fishes and mammals have traditionally been described in taxa-specific journals. However, mixed-species systems are actually more widely found when one includes aggregative (non-moving) systems, such as those common in amphibians and invertebrates. The objective of this special issue is to dispel the idea that mixed-species phenomena are a ‘niche topic’ to ecology and instead explore how taking a mixed-species perspective can change our conception of important ecological patterns and processes. A mixed-species perspective starts by understanding the relative abundance and positioning of individuals of different species and their behavioural synchrony; it is enriched by understanding differences between species in their vulnerability/attractiveness to predators, their potential for competing with other group participants and their use as a source of public information. Contributions to the special issue show how the mixed-species perspective can change our ideas about invasion ecology, island biogeography, keystone species, mimicry, predator eavesdropping and more. Rather than seeking synthesis, the special issue celebrates the taxonomic and conceptual breadth of the field of mixed-species groups, with detailed descriptions of many distinctive systems. This article is part of the theme issue ‘Mixed-species groups and aggregations: shaping ecological and behavioural patterns and processes’.

Mixed-species flock sizes and compositions influence flock members’ success in three field experiments with novel feeders

“…Flocks contained an average of 3.89 ± 1.77 (2-8) titmice and 1.39 ± 0.99 (0-4) nuthatches. Mean MSF size was 11.19 ± 3.03 (5)(6)(7)(8)(9)(10)(11)(12)(13)(14)(15)(16)(17) individuals and mean diversity index across flocks was 3.01 ± 0.93 (1.32-4.84). Feeders with the diverse seed mix attracted a median of 4 birds (range 2-7) compared to a median of 3.5 birds (range 2-5) for feeders with the regular seed mix (n 1 = 18, n 2 = 18, U = 87, p = 0.015).…”

“…Such benefits could also simply be a by-product of the fact that mixed-species groups are often larger than single-species groups, and larger groups are more likely to have one individual solve a problem (e.g., food or predator detection), by skill or by chance, than smaller groups [ 14 ]. Increased research on mixed-species groups is needed to understand better the specific factors that influence group- and individual-level success at salient problems faced by group members, including avoiding predation, finding food, moving, and staying cohesive [ 5 ].…”

“…Individuals living in groups typically benefit from being part of those groups by improved ability to avoid predation and find food and other important resources [1,2]. It is becoming increasingly clear, furthermore, that these benefits can be just as great-and perhaps greaterfor species regularly occurring in mixed-species groups [3][4][5][6][7]. For example, Diana monkeys (Cercopithecus diana) and Campbell's monkeys (C. campbelli) shift the height they forage in the canopy when in mixed groups, resulting in both species spending less time being vigilant and more time successfully foraging than when they are in groups of only conspecifics [8].…”

Multispecies collective waving behaviour in fish

“…While these differences are found among individuals of the same populations and species and even among clonal individuals [21], even stronger differences among members of a collective can be assumed when looking at mixed-species aggregations. which are common in birds [22,23], ungulates [24][25][26] and fishes [27][28][29]-taxa that also provide examples of some of the largest known animal collectives [30] and are the focus of recent scientific interest [31].…”