Table 2. Cluster statistics under paraphyletic and monophyletic clustering.

‘No bootstrap’ corresponds to paraphyetic clustering with b_min = 0; otherwise this threshold defaults to 95%. Optimal d_max is the pairwise distance threshold selected by minimizing ΔAIC, in units of expected number of nucleotide substitutions. ‘Number of clusters’ only counts clusters with two or more background sequences, i.e., this number does not include singletons. Total growth is the number of incident (new) sequences connected to clusters of background sequences. Growing clusters is the number of clusters to which incident sequences attach.

Location	Optimal	Number of	Mean	Largest	Total	Growing
	d max	clusters > 1	cluster size	cluster size	growth	clusters
Washington, USA	0.013	74	1.39	1657	68	30
No bootstrap	0.008	378	2.04	1560	73	36
Monophyletic	0.016	639	1.20	16	92	96
Alberta, Canada	0.007	104	1.35	58	34	27
No bootstrap	0.006	228	1.75	28	45	28
Monophyletic	0.002	26	1.04	4	52	64
Tennessee, USA	0.012	1	1.35	358	41	28
No bootstrap	0.008	621	1.91	78	41	35
Monophyletic	0.020	360	1.29	11	63	53
Beijing, China	0.008	135	1.82	533	373	119
No bootstrap	0.006	409	2.49	381	305	127
Monophyletic	0.032	490	2.13	46	613	275