8.4 Dispersal and philopatry

Dispersal and philopatry are crucial aspects of animal behavior that shape population dynamics and evolution. These movements, or lack thereof, influence gene flow, social structures, and adaptation to changing environments.

Understanding dispersal patterns helps explain how animals colonize new habitats, avoid inbreeding, and respond to resource competition. Meanwhile, philopatry reveals the benefits of staying put, like familiarity with an area and maintaining kin relationships.

Types of dispersal

• Dispersal refers to the movement of individuals away from their natal area or social group to reproduce in a new location
• Different types of dispersal can occur at various life stages and have distinct implications for animal behavior and population dynamics

Natal dispersal

Top images from around the web for Natal dispersal

• 

  Search strategies in rural and urban environment during natal dispersal of the red squirrel ... View original

  Is this image relevant?

• 

  Topic 11.4: Sexual Reproduction - AMAZING WORLD OF SCIENCE WITH MR. GREEN View original

  Is this image relevant?

• 

  Movement patterns and habitat selection during dispersal in Eurasian lynx | Mammal Research View original

  Is this image relevant?

• 

  Search strategies in rural and urban environment during natal dispersal of the red squirrel ... View original

  Is this image relevant?

• 

  Topic 11.4: Sexual Reproduction - AMAZING WORLD OF SCIENCE WITH MR. GREEN View original

  Is this image relevant?

1 of 3

Top images from around the web for Natal dispersal

• 

  Search strategies in rural and urban environment during natal dispersal of the red squirrel ... View original

  Is this image relevant?

• 

  Topic 11.4: Sexual Reproduction - AMAZING WORLD OF SCIENCE WITH MR. GREEN View original

  Is this image relevant?

• 

  Movement patterns and habitat selection during dispersal in Eurasian lynx | Mammal Research View original

  Is this image relevant?

• 

  Search strategies in rural and urban environment during natal dispersal of the red squirrel ... View original

  Is this image relevant?

• 

  Topic 11.4: Sexual Reproduction - AMAZING WORLD OF SCIENCE WITH MR. GREEN View original

  Is this image relevant?

1 of 3

• Natal dispersal is the permanent movement of an individual from its birth site to the location where it first reproduces
• Occurs prior to the first breeding attempt and is common in many bird and mammal species
• Natal dispersal can be influenced by factors such as sex, body condition, and population density
• Examples include male-biased dispersal in many mammal species (lions) and female-biased dispersal in some bird species (great tits)

Breeding dispersal

• Breeding dispersal is the movement of an individual between successive breeding attempts, often between years
• Can occur in response to factors such as mate loss, habitat quality, or reproductive success
• Breeding dispersal can be an important strategy for individuals to improve their reproductive prospects or avoid inbreeding
• Examples include divorce and mate switching in birds (albatrosses) and seasonal migrations to breeding grounds in some mammals (gray whales)

Sex-biased dispersal

• Sex-biased dispersal refers to the tendency for one sex to disperse more frequently or farther than the other
• Often driven by mating systems, inbreeding avoidance, or resource competition
• Male-biased dispersal is common in polygynous species where males compete for mates (red deer)
• Female-biased dispersal occurs in some monogamous bird species (Seychelles warblers) and in species with resource defense polygyny (kangaroos)

Factors influencing dispersal

• Multiple ecological and social factors can influence an individual's decision to disperse from its natal area or social group
• Understanding these factors is crucial for predicting dispersal patterns and their consequences for animal populations

Inbreeding avoidance

• Dispersal can serve as a mechanism to avoid mating with close relatives and reduce the risk of inbreeding depression
• Individuals may disperse from their natal group to find unrelated mates and increase offspring fitness
• Sex-biased dispersal can evolve as a strategy to minimize the risk of inbreeding (spotted hyenas)

Resource competition

• Competition for limited resources, such as food or breeding sites, can drive dispersal in animal populations
• Individuals may disperse to reduce competition with siblings or other kin
• Dispersal can also be a response to high population density and resource scarcity (red squirrels)

Habitat quality

• Variation in habitat quality can influence dispersal decisions, with individuals seeking better-quality habitats
• Dispersal may occur when natal habitat quality declines or when better habitat patches become available
• Habitat fragmentation and degradation can also force individuals to disperse in search of suitable areas (Iberian lynx)

Population density

• High population density can increase competition for resources and mates, promoting dispersal
• Density-dependent dispersal has been observed in many species, with increased dispersal rates at higher densities
• In some cases, individuals may also disperse to avoid aggression or social stress in high-density populations (common lizards)

Costs and benefits of dispersal

• Dispersal can have both costs and benefits for individuals, and the balance between these factors shapes dispersal strategies
• Assessing the trade-offs associated with dispersal is essential for understanding its adaptive significance in animal populations

Increased mortality risk

• Dispersing individuals often face higher mortality rates compared to non-dispersers
• Unfamiliar environments, predation, and the energetic costs of movement can contribute to increased mortality during dispersal
• Examples include higher predation risk for dispersing juvenile meerkats and increased mortality during migration in some bird species (Arctic terns)

Reduced familiarity with environment

• Dispersers may lack knowledge about the distribution of resources, predators, and potential mates in new habitats
• Reduced familiarity can lead to lower foraging efficiency, increased predation risk, and difficulty finding suitable breeding sites
• Dispersing individuals may require time to acquire local knowledge and establish themselves in a new area (African elephants)

Potential for better resources

• Dispersal can provide access to higher-quality habitats or resources that are not available in the natal area
• Individuals may disperse to find better foraging opportunities, breeding sites, or mates
• Dispersal can be advantageous when natal habitat quality is low or when there is high competition for resources (beavers)

Reduced competition with kin

• Dispersal can reduce competition with related individuals for resources and mates
• By dispersing, individuals can avoid competing with siblings or other close relatives, which can increase inclusive fitness
• Reduced kin competition can be particularly important in species with limited resources or high reproductive skew (meerkats)

Philopatry

• Philopatry refers to the tendency of an individual to remain in or return to its natal area or social group for breeding
• The study of philopatry is crucial for understanding the evolution of social systems and the maintenance of kin structures in animal populations

Definition of philopatry

• Philopatry is the opposite of dispersal, where individuals stay in their natal area or group rather than moving away
• Can refer to both natal philopatry (remaining in the birth area) and breeding philopatry (returning to the birth area for reproduction)
• Philopatry is common in many social species, particularly those with complex kin structures (killer whales)

Advantages of philopatry

• Philopatric individuals can benefit from familiarity with their natal environment, including knowledge of resources and predators
• Remaining in the natal group allows for the maintenance of social bonds and potential cooperation with kin
• Philopatry can lead to the formation of stable social groups and the inheritance of resources or territories (African elephants)

Kin selection and philopatry

• Kin selection theory predicts that individuals can increase their inclusive fitness by helping related individuals
• Philopatry facilitates interactions among kin and can promote the evolution of cooperative behaviors
• In species with high levels of philopatry, individuals are more likely to interact with and assist close relatives (acorn woodpeckers)

Dispersal strategies

• Dispersal strategies can vary among species and individuals, depending on the ecological and social context
• Different dispersal patterns can have important implications for population structure, social dynamics, and the evolution of cooperative behaviors

Solitary dispersal

• Solitary dispersal involves individuals leaving their natal group or area alone and attempting to establish themselves in a new location
• Common in species where individuals do not form strong social bonds or where resources are widely distributed
• Solitary dispersers may face higher costs, such as increased predation risk or difficulty finding mates (tigers)

Group dispersal

• Group dispersal occurs when multiple individuals, often siblings or members of the same cohort, disperse together
• Can provide benefits such as reduced predation risk, increased foraging efficiency, and social support
• Group dispersal is observed in some social mammals (meerkats) and in species where individuals form coalitions (lions)

Delayed dispersal

• Delayed dispersal refers to the postponement of dispersal beyond the age of sexual maturity
• Individuals may remain in their natal group as non-breeding helpers, assisting in the care of younger siblings or other relatives
• Delayed dispersal is a key component of cooperative breeding systems and can be influenced by ecological constraints or the benefits of group living (red wolves)

Genetic consequences of dispersal

• Dispersal can have significant effects on the genetic structure and diversity of animal populations
• Understanding the genetic consequences of dispersal is essential for predicting population responses to environmental change and for conservation management

Gene flow between populations

• Dispersal facilitates gene flow between populations by allowing individuals to move and reproduce in new areas
• Gene flow can counteract the effects of genetic drift and local adaptation, maintaining genetic diversity within populations
• The extent of gene flow depends on factors such as dispersal distance, dispersal rates, and landscape connectivity (bighorn sheep)

Inbreeding vs outbreeding

• Dispersal can influence the balance between inbreeding and outbreeding in animal populations
• Inbreeding occurs when related individuals mate, which can lead to the expression of deleterious alleles and reduced fitness
• Outbreeding involves mating between unrelated individuals, which can increase genetic diversity and hybrid vigor
• Dispersal can promote outbreeding by allowing individuals to find unrelated mates in new areas (great tits)

Maintenance of genetic diversity

• Dispersal plays a crucial role in maintaining genetic diversity within and among populations
• By facilitating gene flow and reducing the effects of genetic drift, dispersal can help preserve rare alleles and adaptive genetic variation
• Genetic diversity is essential for the long-term persistence and adaptability of populations in changing environments (Florida panthers)

Dispersal in social animals

• Dispersal patterns in social animals are influenced by the complex interplay between individual fitness, kin selection, and group dynamics
• Understanding dispersal in social species is crucial for the study of the evolution of sociality and cooperative behaviors

Cooperative breeding and philopatry

• Cooperative breeding systems are characterized by the presence of non-breeding helpers that assist in the care of offspring
• Philopatry is a key component of cooperative breeding, as it allows for the formation of stable kin groups and the opportunity for helpers to gain indirect fitness benefits
• Dispersal decisions in cooperative breeders are often influenced by factors such as group size, relatedness, and reproductive opportunities (meerkats)

Dispersal in eusocial insects

• Eusocial insects, such as ants and bees, exhibit complex dispersal patterns that are closely tied to their colonial life history
• In many eusocial species, only a subset of individuals (queens and males) disperse for reproduction, while workers remain in their natal colony
• Dispersal in eusocial insects can be influenced by factors such as colony size, resource availability, and mate competition (honey bees)

Dispersal in mammals and birds

• Dispersal patterns in mammals and birds can vary widely depending on the species' social system and ecological context
• In many mammalian species, dispersal is male-biased, with females remaining in their natal group (chimpanzees)
• In birds, dispersal patterns can be influenced by factors such as mating system, resource distribution, and parental care strategies (great tits)

Methods for studying dispersal

• Studying dispersal in wild animal populations can be challenging due to the difficulty of tracking individuals across landscapes
• Various methods have been developed to investigate dispersal patterns, each with its own strengths and limitations

Mark-recapture techniques

• Mark-recapture involves capturing, marking (with tags, bands, or collars), and releasing individuals, then subsequently recapturing them to estimate dispersal distances and rates
• Provides direct information on individual movements but can be labor-intensive and limited by the spatial scale of the study
• Examples include banding studies in birds (barn swallows) and trapping grids for small mammals (voles)

Genetic markers and relatedness

• Genetic markers, such as microsatellites or single nucleotide polymorphisms (SNPs), can be used to infer dispersal patterns based on the spatial distribution of genetic variation
• By comparing the genetic relatedness of individuals across different locations, researchers can estimate dispersal rates and distances
• Genetic methods are particularly useful for studying dispersal in species that are difficult to observe directly (great white sharks)

Radio-tracking and GPS monitoring

• Radio-tracking involves attaching small radio transmitters to individuals and tracking their movements using receivers
• GPS monitoring uses satellite-based tags to record the precise locations of individuals over time
• These methods provide detailed information on individual dispersal trajectories but can be expensive and limited by the size and weight of the devices (Eurasian lynx)

Evolutionary significance of dispersal

• Dispersal is a key evolutionary process that shapes the distribution, adaptation, and diversification of species
• Understanding the evolutionary significance of dispersal is crucial for predicting species' responses to environmental change and for conservation planning

Colonization of new habitats

• Dispersal allows species to colonize new habitats and expand their ranges
• The ability to disperse and establish populations in novel environments can be essential for species' persistence in the face of habitat loss or climate change
• Examples include the colonization of oceanic islands by birds (Darwin's finches) and the range expansions of species in response to glacial retreats (butterflies)

Adaptation to changing environments

• Dispersal can facilitate the spread of adaptive alleles across populations, allowing species to respond to changing environmental conditions
• Gene flow mediated by dispersal can introduce novel genetic variation into populations, promoting adaptive evolution
• Dispersal can also allow individuals to escape deteriorating habitats and settle in areas with more favorable conditions (Glanville fritillary butterfly)

Speciation and diversification

• Dispersal can play a role in the formation of new species by promoting population divergence and reproductive isolation
• Founder events, where a small number of individuals disperse and establish a new population, can lead to rapid evolutionary change and speciation (Hawaiian Drosophila)
• Dispersal can also contribute to adaptive radiations, where species diversify rapidly to fill different ecological niches (Galápagos finches)