Life History Strategies

What are the advantages of having seeds

Genetic recombination, robust package provisioned with nutrients

Theoretical tradeoff of seed mass versus seed number

A fixed amount of resources can be divided into many small units or few large units

When are many small seeds advantageous

When suitable sited or conditions for seedling establishment are unpredictable or patchy

When are large seeds advantageous

Where suitable sired for seedling establishment are predictable but subject to competition

Why would ecosystem factors force seeds to be larger

Trees in mature successional ecosystems may need to produce large seeds with high nutrient stores because seedlings will need provisioned nutrients to survive living in the shaded understory. This then means that the seeds are too large to be transported by things like wind and must be transported by animals

Correlation between seed mass and growth form

Grasses rushes, and sedges, often have small seeds that are not animal dispersed, while woody plants and climbers are more likely to have larger seeds

Important constraint of seed mass and dispersal by animals

Seed mass and size is limited by the largest animal that can eat and disperse it

Comparison of bird sizes in NZ and Australia and how it relates to seed dispersal and mass

Birds in NZ are generally smaller and have smaller gape sizes which leads to smaller seeds and fruits in NZ compared to Australia

Speciation and extinction occur in higher instances among what kind of seeds

Smaller seeds (often have faster lifecycles making for faster speciation and also higher rates of extinction compared to large seeds)

Seedbank definition

Seeds are present in environment but are not above ground as a reproducing plant

What are the dynamics/outcomes within a seed bank

Seeds are dispersed, some are eaten, some decay, some germinate right away and live, others germinate and then die, the rest may stay dormant for long periods of time

Are small or large seeded species more likely to form seed banks

Small seeded species (because they produce more seeds compared to large seeded species. Large seeds are also more likely to be predated)

What traits are associated with being able to form seed banks

Small and round, tough seed coat, starchy endosperm, seed dormancy

Describe the species with seedbanks in New Zealand

It is rare for species to form seed banks in NZ but there is little research on the topic

Examples of species that potentially form seedbanks in NZ

Pikao (seedlings known to appear after disturbance), South Island Kowhai (Canopy seed bank & seeds may persist in the soil), and canopy seed bank in Manuka

2 main different kinds of seed dormancy

Morphological dormancy & physiological dormancy

Morphological dormancy traits

Tough seed coat that requires abrasion or fungal penetration to germinate (legumes)

Physiological dormancy traits

When seed is released from plant it is not mature and requires after ripening, or could have a requirement for light levels or chilling in order to germinate

Orthodox seeds versus recalcitrant seeds

Orthodox seeds are seeds that can be stored for more than 20 years and tolerate drying, Recalcitrant seeds do not tolerate drying (typically large seeds and tropical species)

What kind of seed traits do New Zealand trees exhibit

a lot are desiccation sensitive (18%) and many are also orthodox (23%)

What are monocarpic plants

Plants that only reproduce once (annuals, bamboos)

What are polycarpic plants

Plants that reproduce repeatedly (trees that have mast seeding)

Definition of mast seeding

Synchronous highly variable seed production among years by a population of plants

Benefit of masting in regard to seed predation

Predators are starved in “off” years and satiated in mast years which means that a greater proportion of seeds escape

Benefit of animal dispersal/pollination in regard to mast seeding

Attracts a larger number of animals from further away which means a greater proportion of flowers/pollinated crops are dispersed