Understanding Colonial Wading Bird Metapopulation Dynamics in the NJ Meadowlands and NY Harbor Mentor: Prof. Gareth J. Russell UBM Student: Abraham Rosales

Black-crowned Night Heron chicks

NY Harbor Nesting Sites

Great Egret Nesting Data

Great Egret Total Nesting Data

Research Goals Try to understand the fluctuation of the populations in islands by combining metapopulation ideas with aggregation behaviors. To manage islands’ resources and look at them as a system and not individuals. To help understand the health of the system

What is a Metapopulation? A metapopulation consists of a group of spatially separated populations of the same species which interact via dispersal.

Possible Reasons for Dynamics Aggregation behavior Lower global carrying capacity than the combined nesting capacity of the patches –Distance to foraging areas –Extent of foraging areas –Quality of food Population aging

Aging Hypothesis and Aggregate Behavior As the population of a patch starts reaching maximum capacity, new generations migrate to a different patch. Old populations start to decrease until their patch is no longer attractive to them so they move to a more attractive patch

Model Assumptions Birds have a tendency to come back to previous nesting sites. Birds prefer to nest in large colonies. Birds arrive one at the time in random order. When a bird arrives to the system, it evaluates all the sites and chooses the most attractive.

Simulation Diagram Developed Colony Patch Allocatio n Colony Development Reproductio n Rate Population Dynamics Population Aging New Nesting Population New population Population Death Starting Population

Colony Development Birds arrive in random order Patch allocation is according to: –Attractiveness: Patch Density Aggregate Behavior –Site Fidelity

Patch Allocation

Site Fidelity A bird has the highest fidelity (Fp=2) for the site where it bred in last than for the rest of the sites. If a bird has not bred for the first time, it has a high fidelity (Fp=1.1)for the site where it was last, but it is not as high as If it had bred there. For all other sites, Fp=1.

Site Population Size Attractiveness Colony size Density-dependence Colonial habit Combination

Population Dynamics Reproduction Rate: –Follows the Theta-Logistic Model Current breeding population Global Carrying Capacity

Density-dependence of breeding Total population size Multiplier on breeding Global Limit

Population Dynamics Cont… Offspring Number: –Random Poisson Distribution with reproduction rate R as its mean

Population Dynamics Cont… Population Death: –Random accidental death, constant rate –Death of old age after 15 years Population Aging

Simulated data and Real data

Effects of Varying

Frequency of large population fluctuations

Effects of Varying the intrinsic growth rate r r = 1r = 2

Age and Site Switching

Conclusions 1 The observed dynamics can be explained solely by intrinsic processes (colonial behavior, site fidelity), as follows: –The development of new colonies is initiated by young birds. –Old colonies decline due to mortality of adults and emigration of young birds. –Aggregation behavior accelerates transition in patch dominance.

Conclusions 2 Nature of system-wide limit on reproductive success (theta-G) affects the frequency of switching. Island managers should consider entire system, rather than automatically looking for island-specific causes of population fluctuations.

Acknowledgements Undergraduate Biology and Mathematics Training Program NSF NJIT Rutgers Newark Prof. Gareth Russell