Emily Chen & Kat Eun

OPTIMAL GROUP SIZE, DISPERSAL DECISIONS AND POSTDISPERSAL RELATIONSHIPS IN

FEMALE AFRICAN LIONS(KIMBERLY L. VANDERWAAL,

ANNA MOSSER, CRAIG PACKER, 2009)

BACKGROUND

• Little to no reproductive skew

• Equal breeding opportunities

But still…

• Patterns of dispersal within females

WHY?

• Hypothesis: Dispersal decisions are sensitive to• Pride size• Interpride competition• Natal territory quality

PREDICTIONS

• Dispersal will increase:

-Large pride size

-Low interpride competition

-Low territory quality

• Prides will remain close post-dispersal:

-High natal territory quality

RESEARCH• Where: Serengeti National Park, Tanzania• 2000 km2

• Two habitat types:• Acacia Woodlands• Open-grassland Plains

• Who: 200-300 lions• Neighbor prides• Unrelated• Related• 2, 5, 10 years

METHODS

• How: GPS radio collar

• When: Year of first male takeover

RESULTS

• Probability of female dispersal increased with increasing pride size• Supports within-group competition prediction

• Reproductive success declined when:• Pride size exceeded 11 adult females (woodlands)• Pride size exceeded 6 adult females (plains)

• Prides almost never split unless further recruitment of subadult females increased pride size to a point where individual reproductive success was reduced

Figure1 Two-year per capita reproductive success of females in woodlands (grey bars) and plains (white bars) prides. Pride size is the number of adult females in each pride.

Dispersal• Probability of dispersal

decreased with increasing intergroup competition

• No evidence that territory quality influenced dispersal decisions

• Subadult females more likely to disperse when intragroup competition=high, intergroup competition=low

After dispersal – Territorial overlap

• First few years after dispersal:• Territorial overlap with mother’s pride

• As # of unrelated prides increased, daughter prides moved closer to their mothers’ pride

• High territory quality closer proximity between all neighboring prides BUT only increased overlap between related prides

DISCUSSION

• Clear habitat-specific threshold for dispersal

• When potential pride size exceeded this threshold: ~50% of female cohorts dispersed

• When potential pride size was below threshold: only ~9% dispersed

Existing prides reaction to their daughters’ prides

Figure3 Proximity between maternal and descendant prides after dispersal (see Table 2 for statistics).

Territory Quality - Effect on Territorial Overlap

Territory quality

• Overlap between related neighbors increased with increasing territory quality, even though distance between territory centers did not change

• Habitat quality increased tolerance of related neighbors

CONCLUSIONS

Dispersal will increase:

-Large pride size YES!-Low intergroup competition YES!-Low territory quality YES!

Prides will remain close post-dispersal:

-High natal territory quality YES